CLUSTERS OF LIKE YEARS
Some mention must be made at this point of a so-far unexplained phenomenon, operating on the time-scale of a few years together, which is occasionally very marked and may for the time being override the two-year and 5 1/2-year (and other short-term) fluctuations.
This is the clustering of several years — not always in unbroken succession — with some similar point of character.
An early example is enshrined in the Fimbulvinter legend quoted on pp. 147–8.
Other runs of three severe winters in a row in Europe with very similar wind circulation patterns occurred in 1878–81 and 1939–42.
Sometimes the similarity concerns surprising detail.
One example was the sequence of three ‘skating Christmases’ in England in 1961, 1962 and 1963, with very severe frosts beginning on or just before 25 December with a strong north European anticyclone and easterly winds blowing right across the European plain.
In a moderated degree, with snowy weather or a dry frost sufficient for skating in southern England between 25 and 28 December, the sequence continued for two more years in 1964 and 1965.
(This sequence must be viewed against the background of only seven to ten Christmases in the first fifty years of the century in southern England with any claim at all, on grounds of white frost or snow, to be classed as a ‘white Christmas’.)
Another, similarly precise cluster was shown in the years 1965–71 by a repeated high frequency of northerly winds in the first five days of January over the British Isles: the winds were northerly on 30 per cent of the days, while only 10 per cent had westerly winds.
No other run of years for which we have daily weather maps (i.e. between 1781 and 1786 or from 1861 to date) shows this feature.
The overall average for the first five days of January over this long period was westerly 32 per cent, northerly 7 per cent; and from 1921 to 1932 (another cluster) the frequencies were westerly 73 per cent, northerly 8 per cent.
Other clusters may be seen in the long record of yearly total frequencies of winds from east and northwest, and of calms, at Copenhagen from 1752 to 1893, here shown in fig. 117.
The explanation must presumably lie in some strong feature of the surface heating pattern persisting over the years concerned, probably an anomalous position of a major ocean current boundary such as Namias identified in the North Pacific Ocean in the 1960s and such as we have pointed out (see fig. 23, p. 60) in the northeast Atlantic in the 1690s.
TO BE CONTINUED ...
CLIMATE, HISTORY AND THE MODERN WORLD
Re: CLIMATE, HISTORY AND THE MODERN WORLD
THE DEVELOPMENT OF CLIMATE
Any advice on future weather, over any time-span whatever, must be accompanied by a proviso that the forecast would have to be changed — to a colder regime with a different wind pattern and a different distribution of rain — if volcanic outbursts should occur sufficient to create (and, perhaps, maintain) major dust veils in the stratosphere.
Essentially the same proviso would be needed to provide for the case of possible further volcanic activity adding to any stratospheric veils already in existence at the time of issue of the forecast advice.
The need for these provisos is perhaps most obvious in the case of any forecasts to cover one to ten years ahead, since the whole (or a large part of) the forecast period could be affected by the dust veil from a single great eruption.
But, in fact, the caution is necessary in relation to all the longer time-spans, since changes in the frequency of volcanic explosions such as are known to have taken place in the past could alter the whole prospect, the effect being generally in the direction of cooling if volcanic dust veils should occur.
In looking next at longer time-scales, it will be convenient to consider first the climatic variations produced by nature and not attributable to man.
TO BE CONTINUED ...
Any advice on future weather, over any time-span whatever, must be accompanied by a proviso that the forecast would have to be changed — to a colder regime with a different wind pattern and a different distribution of rain — if volcanic outbursts should occur sufficient to create (and, perhaps, maintain) major dust veils in the stratosphere.
Essentially the same proviso would be needed to provide for the case of possible further volcanic activity adding to any stratospheric veils already in existence at the time of issue of the forecast advice.
The need for these provisos is perhaps most obvious in the case of any forecasts to cover one to ten years ahead, since the whole (or a large part of) the forecast period could be affected by the dust veil from a single great eruption.
But, in fact, the caution is necessary in relation to all the longer time-spans, since changes in the frequency of volcanic explosions such as are known to have taken place in the past could alter the whole prospect, the effect being generally in the direction of cooling if volcanic dust veils should occur.
In looking next at longer time-scales, it will be convenient to consider first the climatic variations produced by nature and not attributable to man.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
CYCLICAL DEVELOPMENTS
In the first place, some apparently cyclic oscillations of longer period than those already mentioned deserve notice.
In all these cases neither their origin nor the outlines of their working in terms of the global wind patterns, which would make it possible to keep a running watch on the evolution of the current round of the oscillation, have yet been properly identified.
Yet variations such as the recurrences of drought in the United States Middle West at roughly 20–23-year intervals must engage the attention — and perhaps precautionary actions — of people (in this case farmers) in the area, whose activities are vulnerable.
The central England temperature record for most seasons of the year (fig. 28, pp. 80– 1) shows variations tending to occur on this same time-scale, which recur in other data around the world and may be triggered by alternate sunspot periods affecting some natural ‘resonance’ period in the atmosphere.
There have been suggestions that the same periodicity is one element in the variations in the occurrence of blocking, specifically of high latitude anticyclones in the Greenland-Iceland-Scandinavia region: but these also show longer-term variations, including perhaps a roughly fifty-year periodicity of which hints were found in the analysis of the many historical manuscript references to seasonal weather over the last nine hundred years in Europe.
Anticyclonic conditions over northern and central Europe appear to have been more frequent in and around the thirties and eighties of most centuries than in the other decades.
The accompanying high frequency of easterly winds, and of calms or light winds, near latitude 50°N, make for a ‘continental’ tendency of the climate in central and western Europe with warm summers and cold winters at such times.
This tendency, however is plainly liable to come into conflict with the effect of any oscillation that is close to twenty years in length.
This brings us to notice the evidence for a cyclical tendency which is very close to a hundred years in length.
Some of the evidence suggests, as in the case of the clustering phenomenon, a surprising approach to precision.
The data in tables 8, 9 and 10 give a survey of some relevant items.
We notice that, whether we consider what is known however roughly of the record since the third century AD or just the last 320 years, for which we have thermometer readings, severe winters seem to have been commoner in the forties and the sixties to nineties of each century than in the other decades.
The bunching of cold winters in and around the sixties and nineties looks interesting and the extraordinary record of the years ending in ninety-five or within one year or so of that.
Although the sample of mild winters is confined to the extremest cases, with winter temperatures at the level normally expected in March, the sequence 1734, 1834 and 1935 accounts for nearly half of them (and there is reason to suppose that 1634 — as well as 1648 — should be added to the table).
Bunching is less obvious in our treatment of the summers, but the concentrations around the years ending in 15–17, 27–31 and 56–63 include over 58 per cent of the very wet summers in England.
Even so, some opposite experiences (summer 1718 had only 56 per cent of the twentieth-century average rainfall, 1818 37 per cent, 1921 57 per cent) occurred close to these dates.
As noted earlier, the ‘blocking’ tendency which is conducive to cold winters in middle latitudes is liable, by a small shift of the controlling anticyclone from one year to another, to produce an extremely mild winter in close proximity to some of the coldest winters: thus the record is dangerous to use in forecasting.
The cyclical tendencies considered in these paragraphs — notably the 2.0-or 2. 2-year, roughly 5 1/2-year, 20–23-year, 50-year and 100-year periods and some others including longer periods, such as 200 years — appear in this or that series of observation data from most parts of the world.
So they are presumably manifestations of certain evolutions in the wind and ocean circulations of worldwide range (whatever external influences, if any, may trigger them off).
However, in many observation series most of them are of only modest amplitude (even if they are to be seen at all) and explain only a small proportion of the variability.
This, and their failure as a guide to the specific year (particularly when opposite extremes can occur), has led most meteorologists to discount their possible value as a forecasting tool.
The position is a very clear warning against ‘juggling with figures’ without a known physical basis.
If these phenomena are to be handled successfully, it is essential to identify their physical origins and acquire some capacity to monitor (and interpret correctly) the unfolding of the phases of the current cycle of the evolution.
There is no denying that some of these cyclical elements in the course of climate development at some times and in some places acquire an importance (e.g. to farmers) not to be ignored.
Some continuing effort to improve the forecasting position is surely demanded.
TO BE CONTINUED ...
In the first place, some apparently cyclic oscillations of longer period than those already mentioned deserve notice.
In all these cases neither their origin nor the outlines of their working in terms of the global wind patterns, which would make it possible to keep a running watch on the evolution of the current round of the oscillation, have yet been properly identified.
Yet variations such as the recurrences of drought in the United States Middle West at roughly 20–23-year intervals must engage the attention — and perhaps precautionary actions — of people (in this case farmers) in the area, whose activities are vulnerable.
The central England temperature record for most seasons of the year (fig. 28, pp. 80– 1) shows variations tending to occur on this same time-scale, which recur in other data around the world and may be triggered by alternate sunspot periods affecting some natural ‘resonance’ period in the atmosphere.
There have been suggestions that the same periodicity is one element in the variations in the occurrence of blocking, specifically of high latitude anticyclones in the Greenland-Iceland-Scandinavia region: but these also show longer-term variations, including perhaps a roughly fifty-year periodicity of which hints were found in the analysis of the many historical manuscript references to seasonal weather over the last nine hundred years in Europe.
Anticyclonic conditions over northern and central Europe appear to have been more frequent in and around the thirties and eighties of most centuries than in the other decades.
The accompanying high frequency of easterly winds, and of calms or light winds, near latitude 50°N, make for a ‘continental’ tendency of the climate in central and western Europe with warm summers and cold winters at such times.
This tendency, however is plainly liable to come into conflict with the effect of any oscillation that is close to twenty years in length.
This brings us to notice the evidence for a cyclical tendency which is very close to a hundred years in length.
Some of the evidence suggests, as in the case of the clustering phenomenon, a surprising approach to precision.
The data in tables 8, 9 and 10 give a survey of some relevant items.
We notice that, whether we consider what is known however roughly of the record since the third century AD or just the last 320 years, for which we have thermometer readings, severe winters seem to have been commoner in the forties and the sixties to nineties of each century than in the other decades.
The bunching of cold winters in and around the sixties and nineties looks interesting and the extraordinary record of the years ending in ninety-five or within one year or so of that.
Although the sample of mild winters is confined to the extremest cases, with winter temperatures at the level normally expected in March, the sequence 1734, 1834 and 1935 accounts for nearly half of them (and there is reason to suppose that 1634 — as well as 1648 — should be added to the table).
Bunching is less obvious in our treatment of the summers, but the concentrations around the years ending in 15–17, 27–31 and 56–63 include over 58 per cent of the very wet summers in England.
Even so, some opposite experiences (summer 1718 had only 56 per cent of the twentieth-century average rainfall, 1818 37 per cent, 1921 57 per cent) occurred close to these dates.
As noted earlier, the ‘blocking’ tendency which is conducive to cold winters in middle latitudes is liable, by a small shift of the controlling anticyclone from one year to another, to produce an extremely mild winter in close proximity to some of the coldest winters: thus the record is dangerous to use in forecasting.
The cyclical tendencies considered in these paragraphs — notably the 2.0-or 2. 2-year, roughly 5 1/2-year, 20–23-year, 50-year and 100-year periods and some others including longer periods, such as 200 years — appear in this or that series of observation data from most parts of the world.
So they are presumably manifestations of certain evolutions in the wind and ocean circulations of worldwide range (whatever external influences, if any, may trigger them off).
However, in many observation series most of them are of only modest amplitude (even if they are to be seen at all) and explain only a small proportion of the variability.
This, and their failure as a guide to the specific year (particularly when opposite extremes can occur), has led most meteorologists to discount their possible value as a forecasting tool.
The position is a very clear warning against ‘juggling with figures’ without a known physical basis.
If these phenomena are to be handled successfully, it is essential to identify their physical origins and acquire some capacity to monitor (and interpret correctly) the unfolding of the phases of the current cycle of the evolution.
There is no denying that some of these cyclical elements in the course of climate development at some times and in some places acquire an importance (e.g. to farmers) not to be ignored.
Some continuing effort to improve the forecasting position is surely demanded.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
FORECASTS OF THE NATURAL CLIMATE
The most accepted forecast of the broad tendency of the natural climate so far issued rests partly on this sort of basis.
In 1974 a specially appointed panel of the National Science Foundation in the United States produced the analysis of the position summarized here in table 11.
The net outcome is a suggestion that the natural climate is at present cooling at an average rate of about 0.15°C per decade.
On this analysis, the net cooling rate would be expected to decline to zero by about the year 2015 and be followed by two or three decades of slight warming, the peak rate being about 0.08°C per decade around AD 2030, and thereafter little change before a further decline a century later.
The variations considered in this treatment over periods of about 100, 200 and 2000 years (or, as some writers would have it, 250 and 2500 years) are perhaps generally thought to be solar in origin, although some variations of the tidal forces may be involved.
Traces of a periodic variation of about 200 years period-length have also been reported in the (global total) volcanic activity; if real, these could contribute to the climatic swings and perhaps help in the forecasting problem.
When we come to the longest periods of variation here mentioned, it is no longer necessary to limit any forecast entirely to a statistical statement.
The amplitudes of the temperature changes are bigger, and they apparently rest on the well-understood changes in the Earth's orbital arrangements, which — like other astronomical variations — can be predicted with some precision.
The associated changes in radiation available to heat the Earth at different seasons can be similarly calculated.
Nevertheless, the effects in terms of temperature (and consequential changes in the wind circulation and rain and snow distribution) are amplified presumably by the reflectivity of an increasing area of snow and ice.
And the changes are at times greatly sharpened in some way, perhaps by volcanic activity and the dust veils produced.
Another suggestion — put forward by Professor A.T. Wilson of the University of Waikato, New Zealand — is that towards the end of each warm interglacial period the remainder of the great inland ice on Antarctica tends to become unstable.
And it is thought that, aided by melting at the base, virtually the whole ice dome covering West Antarctica — the Pacific Ocean sector of the continent — where the bed-rock is far below sea level is liable to surge out into the surrounding sea (and perhaps parts of the bigger East Antarctic dome as well).
This should so broaden the floating pack-ice belt as to cool the entire southern hemisphere climate and ultimately cool the oceans all over the world.
Hence, the magnitude and the timing of the more abrupt steps in the climatic progression are subject to influences, such as the incidence of volcanic dust in the atmosphere, and perhaps Antarctic ice surges, which may have to be treated as random.
This means that details of timing of the progression towards another ice age can probably only be stated in some sort of statistical terms based on comparisons with the declining stages of previous interglacials.
The most thorough refinement of the calculation of the Earth’s orbital variations, extending back (for each month of the year at thousand-year intervals) over the last million years and forward sixty thousand years into the future, has been carried out by Professor A. Berger of the Institute of Astronomy and Geophysics at the Catholic University of Louvain-la-Neuve, Belgium.
Berger has also been able to demonstrate a convincing (statistically significant) association between these variations and past climatic effects on the scale of ice ages and interglacial periods.
This was done by studying with Dr G. Kukla of the Lamont-Doherty Geological Observatory, New York, the significance of the climatic response to the radiation changes in different months of the year and at various latitudes.
Two different models were used for examining the association between the radiation balance variations and the climatic response.
One model examined the incidence of warm and cold climate periods separately; the other amounted to a single integrated expression of the regime, including a persistence effect from the condition of the climate three thousand years before.
The results from the two models agreed so well, and they explained such a high proportion (in one case 87 per cent) of the past climatic variation (as known from the oxygen isotope variations in cores from the bed of the deep oceans), that in Berger’s words they ‘authorize the prediction of the future natural climate’.
The result is seen in the righthand portion of fig. 118.
The key points are that:
1 Unless counter-effects due to man's impact on the climate supervene, the descent of prevailing temperatures towards the next ice age is due to steepen in the next millennia.
2 The first (modest) climax of colder, more or less glacial climate appears to be only around three thousand to seven thousand years from now.
3 Despite some recovery peaking about fifteen thousand years hence, return to climates as warm as today’s is not expected until after a full glacial climax about sixty thousand years hence.
According to one of the models used, 114,000 years of glacial climates lie ahead.
This outline of the development of climate over all these thousands of years ahead may be regarded as the most guaranteeable part of our capacity to foresee the future, because its basis is of similar nature to the succession of night and day and the yearly round of the seasons.
These findings explain the importance attached in some quarters to studies of the declining stages of the last warm interglacial period after its peak about 120,000–125,000 years ago.
The detailed curve from north-west Greenland which we have shown in fig. 35 (p. 92) looks less drastic between 120,000 and 90,000 years ago than the past record as represented by fig. 118, though there are features 5000–8000 years after the peak of the last interglacial which could signify effects that would be alarming today.
It behoves us to look into the evidence from other parts of the world, and this commonly produces a sharper feature around the time mentioned, more like that seen in fig. 118.
The most detailed record we have for the period of interest is the pollen record from a peat-bog at Grand Pile in the Vosges mountains in north-east France, examined by Dr Geneviève Woillard of Louvain-la-Neuve.
This is the longest continuous pollen record so far obtained anywhere in the world, going back right through the last ice age and the interglacial before it to 140,000 years ago (at which date an early post-glacial type of vegetation was present).
Only for 11,000 years around 125,000 years ago does the pollen from the surrounding vegetation indicate a climate as warm as in the current post-glacial times up to the present.
Then, as with the ending of the temperate stages of other interglacials examined elsewhere, a series of abrupt changes of the vegetation character followed.
The changes at the end of the warmest part of the interglacial, which it was possible at Grande Pile to follow in close detail, indicate that the change-over from a temperate fir-spruce forest mixed with alder, box, hornbeam and oak to a typical boreal forest dominated by pine, birch and spruce, as in Scandinavia today, took only about 150 years.
(The error margin on this estimate is not thought likely to exceed seventy-five years either way.)
There seem to have been three quite abrupt stages in the transition, the first marked by decline of all the broad-leafed trees but most notably by a sharp decline of the fir (Abies) which had been present.
The most drastic change took place 150 years later, when within 20 years the remaining fir and the broad-leafed trees virtually disappeared.
It is suggested by those engaged in this work that the first sharp decline of fir may have been due to a very dry hot summer — the case of 1976 had a similar effect — but that most details of the transition point to a net cooling of the climate.
(Perhaps the current European and North American elm disease is part of a similar picture.)
And it is claimed that, although it has never been possible to indicate the detailed timing before, these changes are typical for the corresponding stage of all interglacial periods that have been examined.
As Dr Woillard warned, we cannot exclude the possibility that we are already living today in the beginning stages of the corresponding vegetation changes and the fact may be masked from our perception by the extent of artificial management of forests.
Meteorologists engaged in climatic research have thought it best to treat the forecasting of the next ice age development in statistical terms.
Whether referring to the orbital variations or to a random variation of volcanic activity as the supposed cause, they have rated the probability of ice age onset within the next hundred years as of the order of 1 or 2 per cent and so as a risk that may be ignored.
However, a change in middle latitudes from an oak-to a birch-and pineforest climate must come much sooner; the lessons of previous warm interglacial times suggest that that change should be expected to have several abrupt stages, and its beginning could quite well be imminent.
A specific forecast, giving perhaps excessive weight to the not adequately explained 200 and 2000–2500 year cyclical tendencies, would probably expect the change to a birch-and pineforest regime between about 3300 and 4300 AD, and one such pronouncement has in fact appeared in print from an internationally respected scientist working in the field.
But, if we were to take the view that most of the recovery in the last hundred years or so from the Little Ice Age climate of recent centuries is attributable to man's output of carbon dioxide into the atmosphere, it may be that the unmodified natural climate would already be nearly at that change-over stage.
This suggests that if we had a physical basis for making a statistical estimate, the probability of the required further (sharp?) cooling of the natural climate to a pine-forest regime occurring within the next 20–200 years could be around 10 per cent or higher.
TO BE CONTINUED ...
The most accepted forecast of the broad tendency of the natural climate so far issued rests partly on this sort of basis.
In 1974 a specially appointed panel of the National Science Foundation in the United States produced the analysis of the position summarized here in table 11.
The net outcome is a suggestion that the natural climate is at present cooling at an average rate of about 0.15°C per decade.
On this analysis, the net cooling rate would be expected to decline to zero by about the year 2015 and be followed by two or three decades of slight warming, the peak rate being about 0.08°C per decade around AD 2030, and thereafter little change before a further decline a century later.
The variations considered in this treatment over periods of about 100, 200 and 2000 years (or, as some writers would have it, 250 and 2500 years) are perhaps generally thought to be solar in origin, although some variations of the tidal forces may be involved.
Traces of a periodic variation of about 200 years period-length have also been reported in the (global total) volcanic activity; if real, these could contribute to the climatic swings and perhaps help in the forecasting problem.
When we come to the longest periods of variation here mentioned, it is no longer necessary to limit any forecast entirely to a statistical statement.
The amplitudes of the temperature changes are bigger, and they apparently rest on the well-understood changes in the Earth's orbital arrangements, which — like other astronomical variations — can be predicted with some precision.
The associated changes in radiation available to heat the Earth at different seasons can be similarly calculated.
Nevertheless, the effects in terms of temperature (and consequential changes in the wind circulation and rain and snow distribution) are amplified presumably by the reflectivity of an increasing area of snow and ice.
And the changes are at times greatly sharpened in some way, perhaps by volcanic activity and the dust veils produced.
Another suggestion — put forward by Professor A.T. Wilson of the University of Waikato, New Zealand — is that towards the end of each warm interglacial period the remainder of the great inland ice on Antarctica tends to become unstable.
And it is thought that, aided by melting at the base, virtually the whole ice dome covering West Antarctica — the Pacific Ocean sector of the continent — where the bed-rock is far below sea level is liable to surge out into the surrounding sea (and perhaps parts of the bigger East Antarctic dome as well).
This should so broaden the floating pack-ice belt as to cool the entire southern hemisphere climate and ultimately cool the oceans all over the world.
Hence, the magnitude and the timing of the more abrupt steps in the climatic progression are subject to influences, such as the incidence of volcanic dust in the atmosphere, and perhaps Antarctic ice surges, which may have to be treated as random.
This means that details of timing of the progression towards another ice age can probably only be stated in some sort of statistical terms based on comparisons with the declining stages of previous interglacials.
The most thorough refinement of the calculation of the Earth’s orbital variations, extending back (for each month of the year at thousand-year intervals) over the last million years and forward sixty thousand years into the future, has been carried out by Professor A. Berger of the Institute of Astronomy and Geophysics at the Catholic University of Louvain-la-Neuve, Belgium.
Berger has also been able to demonstrate a convincing (statistically significant) association between these variations and past climatic effects on the scale of ice ages and interglacial periods.
This was done by studying with Dr G. Kukla of the Lamont-Doherty Geological Observatory, New York, the significance of the climatic response to the radiation changes in different months of the year and at various latitudes.
Two different models were used for examining the association between the radiation balance variations and the climatic response.
One model examined the incidence of warm and cold climate periods separately; the other amounted to a single integrated expression of the regime, including a persistence effect from the condition of the climate three thousand years before.
The results from the two models agreed so well, and they explained such a high proportion (in one case 87 per cent) of the past climatic variation (as known from the oxygen isotope variations in cores from the bed of the deep oceans), that in Berger’s words they ‘authorize the prediction of the future natural climate’.
The result is seen in the righthand portion of fig. 118.
The key points are that:
1 Unless counter-effects due to man's impact on the climate supervene, the descent of prevailing temperatures towards the next ice age is due to steepen in the next millennia.
2 The first (modest) climax of colder, more or less glacial climate appears to be only around three thousand to seven thousand years from now.
3 Despite some recovery peaking about fifteen thousand years hence, return to climates as warm as today’s is not expected until after a full glacial climax about sixty thousand years hence.
According to one of the models used, 114,000 years of glacial climates lie ahead.
This outline of the development of climate over all these thousands of years ahead may be regarded as the most guaranteeable part of our capacity to foresee the future, because its basis is of similar nature to the succession of night and day and the yearly round of the seasons.
These findings explain the importance attached in some quarters to studies of the declining stages of the last warm interglacial period after its peak about 120,000–125,000 years ago.
The detailed curve from north-west Greenland which we have shown in fig. 35 (p. 92) looks less drastic between 120,000 and 90,000 years ago than the past record as represented by fig. 118, though there are features 5000–8000 years after the peak of the last interglacial which could signify effects that would be alarming today.
It behoves us to look into the evidence from other parts of the world, and this commonly produces a sharper feature around the time mentioned, more like that seen in fig. 118.
The most detailed record we have for the period of interest is the pollen record from a peat-bog at Grand Pile in the Vosges mountains in north-east France, examined by Dr Geneviève Woillard of Louvain-la-Neuve.
This is the longest continuous pollen record so far obtained anywhere in the world, going back right through the last ice age and the interglacial before it to 140,000 years ago (at which date an early post-glacial type of vegetation was present).
Only for 11,000 years around 125,000 years ago does the pollen from the surrounding vegetation indicate a climate as warm as in the current post-glacial times up to the present.
Then, as with the ending of the temperate stages of other interglacials examined elsewhere, a series of abrupt changes of the vegetation character followed.
The changes at the end of the warmest part of the interglacial, which it was possible at Grande Pile to follow in close detail, indicate that the change-over from a temperate fir-spruce forest mixed with alder, box, hornbeam and oak to a typical boreal forest dominated by pine, birch and spruce, as in Scandinavia today, took only about 150 years.
(The error margin on this estimate is not thought likely to exceed seventy-five years either way.)
There seem to have been three quite abrupt stages in the transition, the first marked by decline of all the broad-leafed trees but most notably by a sharp decline of the fir (Abies) which had been present.
The most drastic change took place 150 years later, when within 20 years the remaining fir and the broad-leafed trees virtually disappeared.
It is suggested by those engaged in this work that the first sharp decline of fir may have been due to a very dry hot summer — the case of 1976 had a similar effect — but that most details of the transition point to a net cooling of the climate.
(Perhaps the current European and North American elm disease is part of a similar picture.)
And it is claimed that, although it has never been possible to indicate the detailed timing before, these changes are typical for the corresponding stage of all interglacial periods that have been examined.
As Dr Woillard warned, we cannot exclude the possibility that we are already living today in the beginning stages of the corresponding vegetation changes and the fact may be masked from our perception by the extent of artificial management of forests.
Meteorologists engaged in climatic research have thought it best to treat the forecasting of the next ice age development in statistical terms.
Whether referring to the orbital variations or to a random variation of volcanic activity as the supposed cause, they have rated the probability of ice age onset within the next hundred years as of the order of 1 or 2 per cent and so as a risk that may be ignored.
However, a change in middle latitudes from an oak-to a birch-and pineforest climate must come much sooner; the lessons of previous warm interglacial times suggest that that change should be expected to have several abrupt stages, and its beginning could quite well be imminent.
A specific forecast, giving perhaps excessive weight to the not adequately explained 200 and 2000–2500 year cyclical tendencies, would probably expect the change to a birch-and pineforest regime between about 3300 and 4300 AD, and one such pronouncement has in fact appeared in print from an internationally respected scientist working in the field.
But, if we were to take the view that most of the recovery in the last hundred years or so from the Little Ice Age climate of recent centuries is attributable to man's output of carbon dioxide into the atmosphere, it may be that the unmodified natural climate would already be nearly at that change-over stage.
This suggests that if we had a physical basis for making a statistical estimate, the probability of the required further (sharp?) cooling of the natural climate to a pine-forest regime occurring within the next 20–200 years could be around 10 per cent or higher.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
POSSIBLE EFFECTS OF HUMAN ACTIVITY AND POLICY DECISIONS
Having thus completed our review of how far the present state of knowledge enables us to make useful statements about the current and future tendencies of the natural climate, we must consider how man's activities may modify the prospect.
This is more difficult even than attempting to forecast the natural climate, because it involves forecasting what mankind will do.
We will assume here that man will refrain from blowing himself up and making the planet uninhabitable with nuclear fall-out.
Past history suggests some pessimism about the likelihood of blame for climatically induced difficulties and changes of land-use (particularly any change in food resources) being imputed to this or that class or nation.
One may also expect fierce competition to grab any dwindling resources, quite apart from the immediate political contentions of the present day.
Mankind is doubtless capable of continuing to inhabit the Earth and survive through the next ice age, and of doing so far better than our primitive forebears who survived the last one.
And we should be at least equally able to adapt to a much warmer Earth with the productive crop belts and the deserts shifted poleward.
But there is no warrant for the unfulfillable hopes — in extraordinarily many quarters today the basic assumption — that a constant, or even a steadily rising, standard of living can be achieved.
In what follows we shall also assume — as is common practice, though seldom specifically said — that the solution to the riddle of the lack of any demonstrable effect from the increase of carbon dioxide so far is that the expected warming has been offset by tendencies of the natural climate working in the opposite direction.
It is agreed by most of those actively engaged in climate modelling that the main threat from human activities to the stability of the existing natural climate regime, to which our present day international order is adapted, is the warming — possibly inconveniently large — to be expected from the continuing increase of carbon dioxide.
And this, as we saw in the last chapter, may be boosted as much as 50 per cent by other pollutants which have a similar action upon the radiation balance.
Later in the twenty-first century, at some point which will depend on how much power is generated from nuclear or other fuels, the output of artificially produced heat may itself begin to have effects on a global scale.
This is certainly the major effect on climate to be expected from the large-scale use of nuclear energy.
In some ways it is analogous to the unsolved problem of disposal of the nuclear waste itself (a problem to which there may be no solution on an Earth where no part of the crust can be guaranteed earthquake-free over the periods of continuing dangerous radioactivity).
There may be climatic troubles arising from the emission of great quantities of heat whatever the locations chosen for electrical power generation.
Some studies have already been directed towards discovering what sort of effects on the world climate pattern might be expected to result from the disposal of the waste heat from nuclear power generation in various parts of the world's oceans.
Various alternative potential sources of energy open to man are under consideration: absorption of solar energy, either directly to be stored as heat in water systems or on a vastly larger scale in the world's deserts to produce electricity, tapping of thermal energy from the oceans, harnessing the power of the tides, growing fuel to burn in the shape of either wood or oil producing crops, use of wind power, and so on.
Not all of these are free from awkward side effects.
According to one estimate, the heliostat arrays required for conversion of solar energy to satisfy the projected demand for the expected population of the Earth — assumed to have doubled — before the middle of the next century would need to cover nine million square kilometres, or about 6 per cent of the total land area of the globe, if only this source of energy were used.
The tapping of potential energy from the oceans would change their temperature distribution, affecting the wind and ocean circulation and hence the climate, and causing them to release carbon dioxide to the atmosphere.
Perhaps only the large-scale use of power from the winds and the tides, for which the technology still needs to be mastered, would be free of major objections.
Nevertheless, all these alternative sources of energy are probably preferable to either fossil fuel or nuclear energy.
Strategies for their most effective use should certainly be explored vigorously and put into practice wherever appropriate.
In the case of most of these types of resource, the proportion of their world total availability which could in fact be used may be rather small, but in some cases the world totals are very large.
And with each type local circumstances govern strongly how much advantage is to be obtained, most obviously so with hydroelectricity or harnessing the power of wind and tides.
Overall, their potential contribution to our energy needs is by no means negligible.
Whatever values we accept for the effects on world climate of the exploitation of various fossil fuels and other sources of energy, the outcome to be expected will depend to an important extent on decisions as to how far to develop each.
Fig. 119 indicates the range of curves currently being put forward for the probable course of the carbon dioxide proportion in the atmosphere over the next centuries.
Curve A is based on the proposition that all the Earths readily exploitable fossil fuel will be burnt within the next two hundred years.
As a result the CO2 proportion in the atmosphere would rise to more than eleven times the natural level that existed before the nineteenth-century acceleration of the Industrial Revolution.
At the other extreme, curve B presents the least change from the pre-existing natural conditions that seems in any way conceivable, the proposition being that power production can be so managed that the CO2 level shall not come to exceed one and a half times the nineteenth-century level.
Curves C and D are taken from the work by Jill Williams and colleagues at the International Institute for Applied Systems Analysis at Schloss Laxenburg, near Vienna, already cited above.
Curve C represents the outlook if artificial energy production continues to grow, but at a more modest rate than in curve A, and nuclear power is not used; curve D represents an ‘optimistic’ energy strategy which keeps down the consumption of oil and coal.
Curve E illustrates the results of another strategy of decisions studied by F. Niehaus of the International Atomic Energy Agency, allowing more use of coal than curves B or D.
These curves certainly identify the increase of carbon dioxide in the atmosphere as one of the most alarming changes of the natural environment due to man and require its potential impact on the climate to be taken with the utmost seriousness.
Discussion of which of the curves in fig. 119 is likely to prove the most realistic has included the —possibly too optimistic — conception that decisions affecting the bulk of the world's energy production may come to be aimed at reducing the dangers inherent in such a drastic modification of nature.
At the other extreme, questions arise of how rapidly the world's oil and coal reserves could in fact be exploited as the portions easiest of access get used up, as well as the problems of how rapidly a switch from one type of fuel and fuel policy to another could be implemented.
The question whether the world's population will really double again also comes into it.
Birth rates are now falling in almost every country in the world (e.g. in China by 41 per cent between 1970 and 1975); and although improving availability of medical services in the Third World may be expected to lower the death rates from disease, rising death rates were in fact reported in the 1970s in a number of poorer countries — particularly in the Indian sub-continent — due to starvation following harvest failures and other natural disasters.
The energy growth situation has already begun to be affected by dawning appreciation of the squandering of limited resources, leading to price rises, and the first beginnings of the idea of strategies to reduce energy demand.
The latter ultimately entails rethinking even in architecture and clothing habits and will undoubtedly require a few decades to evolve.
At present consumption rates there will be no more fossil fuels after about AD 2200, though the enchanced CO2 in the atmosphere will be with our descendants for long after that: political decisions to reduce consumption and so spin the process out can, of course, be expected long before exhaustion of the fossil fuels is reached.
Thus the first part of the projection into the future in fig. 119 is at least on fairly firm ground in expecting less change of present growth rates than may later on be achieved.
What is clear is that the possible warming of world climates due to carbon dioxide chiefly concerns the next few centuries as the CO2 builds up and, on the present showing of human behaviour, reaches a peak with the exhaustion of fossil fuels sometime between AD 2100 and 2600.
Thereafter the atmospheric CO2 proportion is expected to decline slowly over many hundreds of years.
Theoretical modelling suggests that in AD 3500 the proportion will still be 70 per cent above the pre-industrial level.
Fig. 120 shows the range of various publicized forecasts of world temperature change based on the carbon dioxide warming effect resulting from different assumed fuel policies.
To put the prospect in perspective against the net outcome when natural climatic variations are also included, what is known in outline of the history of world temperature from the seventeenth century to date is indicated by the most widely accepted variations of five-year mean temperature level in central England and over the northern hemisphere (the latter available only since 1870).
This makes it obvious that the CO2 climate theory is not doing very well as the sole explanation of the changes and that other causes of climatic variation are also important.
The common decision to treat the natural climatic variations as unforecastable ‘noise’ (i.e. random events) is plainly not satisfactory.
Research effort must be continued, aimed at improving our capacity to foresee the variations of the natural climate.
Nevertheless, widely publicized expert opinion from the leading theoretical modelling laboratories in climatic research expects the increase of CO2 to have raised world temperature by between 1 and 2°C by the period AD 2050–2100 in the case of the most restrictive strategies on fossil fuel consumption and by from 4 to 9°C (refer to fig. 114 and text on pp. 334–6) on the basis of what are thought to be likelier developments.
These figures may even be increased by the contributions from other pollutants.
Changes of this magnitude imply bringing world temperature to a level which has not occurred in the last two million years, since the Tertiary geological period.
The polar sea ice would be expected to melt and disappear, but the great masses of inland ice covering Greenland and Antarctica would take a long time to go.
This is just as well, since melting of the Greenland ice-cap alone would raise world sea level by 6 or 7 m, while the addition of water from the Antarctic inland ice would ultimately — after a delay of some centuries as melting proceeded — raise the oceans by between 50 and 100 m, submerging lowland plains in every continent and drowning nearly all the world’s great cities.
Clearly the proposed change of world temperature level would also shift all the vegetation and crop belts poleward by many degrees of latitude, and this would take more or less immediate effect, dislocating the existing economies of nations.
Research aimed at studying the geographical distribution of expected climatic effects at each stage of the progression towards this artificial world of the twenty-first century is therefore seen as urgent.
Many exploratory studies have already been done.
Some use theoretical models of the climate system.
Others proceed by studying the climate patterns of various warm periods in the past.
These ‘scenarios’, as they are called, start with the regime in the earlier part of the present century and/or the patterns of individual warm years, a level commonly expected (on the basis discussed) to return within a decade or two.
The next stage is likened to the medieval warm epoch, with average temperature over much of the northern hemisphere around 1°C above present.
Thereafter, stages equivalent to the warmest post-glacial times, to the warmest part of the last interglacial periods, and to the late Tertiary geological epoch, are supposedly reached in succession, within at most six hundred years: the conditions of those times may therefore be relevant studies.
The general tenor of the conclusions may be summarized as follows:
1 The temperature rise over the Arctic regions generally is expected to be several times as great as the world average.
For the first doubling of the CO2 level a warming by 8–10°C near latitude 80°N is suggested.
2 With so big a change of temperature gradients, and of their position, and of that of such ice surface boundaries as would still be present, the patterns (and intensity) of the world’s wind and ocean circulations would be shifted and changed.
3 The changes of the wind and ocean circulations would alter the distribution and amounts of rain and snowfall.
The expected temperature changes have been widely announced in an ever increasing volume of meteorological literature, notably at the World Climate Conference organized by the World Meteorological Organization in February 1979 and at other scientific conferences before and since.
The alarm that has been raised over the dislocation which such great changes would be liable to cause is entirely proper, even though the actual net outcome when the natural climatic variations also have their effect (and even our view of the CO2 effect itself when the theoretical modelling has been improved) is by no means certain.
There is not very much time to acquire the necessary further knowledge to resolve this question and only too little time to adapt national and international habits and policy in the use of energy to minimize the dangers ahead — especially since some radical changes may be called for.
The dilemma is a very difficult one.
Despite the uncertain reputation of even short-term weather forecasts, and the uncertainties involved in this rather different problem, the potential for disorganization and disaster is so great that the meteorologists’ warnings must be taken as a very serious matter.
Nor is it only the temperature changes that look serious.
The changes of precipitation, and of the balance between down-put and evaporation, would also be important.
Although precipitation would be expected to increase at most latitudes because of the extra water vapour picked up from warmer seas, it is only in high latitudes and the monsoon regions of Asia that a general increase above the increased rate of evaporation would be expected.
Over most of the northern hemisphere’s land-masses conditions could turn out significantly drier than today’s.
And, as the warming should move the belts of cyclonic activity polewards, the Mediterranean winter rains would be expected to fail.
Indeed, at that latitude (35–40°N) total rainfall would probably decrease; with more evaporation there, as elsewhere, the aridity of the desert would presumably advance over the region.
The patterns that have to be considered if and when the generation of nuclear power, and the waste heat from this and from the cities of the future besides, begin to affect the climate on a global scale differ from those arising in the CO2 problem.
The artificial generation of heat is now, and presumably always will be, concentrated in limited areas.
Globally, the heat artificially generated today is only about one ten-thousandth part of the energy absorbed at the Earth’s surface from the sun.
And it seems unlikely to rise above one half of one per cent within the next century or two, possibly implying a rise of world temperature by about 1°C.
But already in some great urban and industrial areas the artificial production of heat is more than a thousand times the world average, and in certain cases exceeds locally the average heat absorbed directly from the sun.
For the possible generation of much larger amounts of heat from nuclear power production to meet future demand, the impact of heat input concentrated in various specially chosen ‘energy park regions’ in the ocean has been investigated.
This has been done by theoretical work using a ‘general circulation model’, in a collaboration between the United Kingdom Meteorological Office and the International Institute for Applied Systems Analysis (IIASA).
The possible energy parks considered were (a) just southwest of the British Isles, (b) in the region of the Cape Verde Islands near 17°N in the eastern Atlantic, and (c) east of Japan, as well as various combinations of these.
In view of inadequacies of present modelling capacity to explore interactions between atmosphere and ocean, huge inputs of heat of probably unrealistic magnitude — to supply a world population five times as big as at present and with a per capita energy consumption ten times the present average — were considered in the theoretical modelling experiments.
This was done in order to make sure of getting an identifiable response, standing out above the random variations.
It was found that there were effects on the large-scale atmospheric circulation which varied according to where the heat was put in, and how much heat, and what proportion went into the ocean and what was allowed to escape into the atmosphere.
But for the smaller heat inputs that might in fact be realized it is suggested that there might be no significant effect on the climate system.
This aspect of nuclear energy seems therefore to entail much less difficulty or danger than the carbon dioxide produced from burning traditional fuels (but, of course, this has nothing to do with the problem of radioactivity of the nuclear waste).
TO BE CONTINUED ...
Having thus completed our review of how far the present state of knowledge enables us to make useful statements about the current and future tendencies of the natural climate, we must consider how man's activities may modify the prospect.
This is more difficult even than attempting to forecast the natural climate, because it involves forecasting what mankind will do.
We will assume here that man will refrain from blowing himself up and making the planet uninhabitable with nuclear fall-out.
Past history suggests some pessimism about the likelihood of blame for climatically induced difficulties and changes of land-use (particularly any change in food resources) being imputed to this or that class or nation.
One may also expect fierce competition to grab any dwindling resources, quite apart from the immediate political contentions of the present day.
Mankind is doubtless capable of continuing to inhabit the Earth and survive through the next ice age, and of doing so far better than our primitive forebears who survived the last one.
And we should be at least equally able to adapt to a much warmer Earth with the productive crop belts and the deserts shifted poleward.
But there is no warrant for the unfulfillable hopes — in extraordinarily many quarters today the basic assumption — that a constant, or even a steadily rising, standard of living can be achieved.
In what follows we shall also assume — as is common practice, though seldom specifically said — that the solution to the riddle of the lack of any demonstrable effect from the increase of carbon dioxide so far is that the expected warming has been offset by tendencies of the natural climate working in the opposite direction.
It is agreed by most of those actively engaged in climate modelling that the main threat from human activities to the stability of the existing natural climate regime, to which our present day international order is adapted, is the warming — possibly inconveniently large — to be expected from the continuing increase of carbon dioxide.
And this, as we saw in the last chapter, may be boosted as much as 50 per cent by other pollutants which have a similar action upon the radiation balance.
Later in the twenty-first century, at some point which will depend on how much power is generated from nuclear or other fuels, the output of artificially produced heat may itself begin to have effects on a global scale.
This is certainly the major effect on climate to be expected from the large-scale use of nuclear energy.
In some ways it is analogous to the unsolved problem of disposal of the nuclear waste itself (a problem to which there may be no solution on an Earth where no part of the crust can be guaranteed earthquake-free over the periods of continuing dangerous radioactivity).
There may be climatic troubles arising from the emission of great quantities of heat whatever the locations chosen for electrical power generation.
Some studies have already been directed towards discovering what sort of effects on the world climate pattern might be expected to result from the disposal of the waste heat from nuclear power generation in various parts of the world's oceans.
Various alternative potential sources of energy open to man are under consideration: absorption of solar energy, either directly to be stored as heat in water systems or on a vastly larger scale in the world's deserts to produce electricity, tapping of thermal energy from the oceans, harnessing the power of the tides, growing fuel to burn in the shape of either wood or oil producing crops, use of wind power, and so on.
Not all of these are free from awkward side effects.
According to one estimate, the heliostat arrays required for conversion of solar energy to satisfy the projected demand for the expected population of the Earth — assumed to have doubled — before the middle of the next century would need to cover nine million square kilometres, or about 6 per cent of the total land area of the globe, if only this source of energy were used.
The tapping of potential energy from the oceans would change their temperature distribution, affecting the wind and ocean circulation and hence the climate, and causing them to release carbon dioxide to the atmosphere.
Perhaps only the large-scale use of power from the winds and the tides, for which the technology still needs to be mastered, would be free of major objections.
Nevertheless, all these alternative sources of energy are probably preferable to either fossil fuel or nuclear energy.
Strategies for their most effective use should certainly be explored vigorously and put into practice wherever appropriate.
In the case of most of these types of resource, the proportion of their world total availability which could in fact be used may be rather small, but in some cases the world totals are very large.
And with each type local circumstances govern strongly how much advantage is to be obtained, most obviously so with hydroelectricity or harnessing the power of wind and tides.
Overall, their potential contribution to our energy needs is by no means negligible.
Whatever values we accept for the effects on world climate of the exploitation of various fossil fuels and other sources of energy, the outcome to be expected will depend to an important extent on decisions as to how far to develop each.
Fig. 119 indicates the range of curves currently being put forward for the probable course of the carbon dioxide proportion in the atmosphere over the next centuries.
Curve A is based on the proposition that all the Earths readily exploitable fossil fuel will be burnt within the next two hundred years.
As a result the CO2 proportion in the atmosphere would rise to more than eleven times the natural level that existed before the nineteenth-century acceleration of the Industrial Revolution.
At the other extreme, curve B presents the least change from the pre-existing natural conditions that seems in any way conceivable, the proposition being that power production can be so managed that the CO2 level shall not come to exceed one and a half times the nineteenth-century level.
Curves C and D are taken from the work by Jill Williams and colleagues at the International Institute for Applied Systems Analysis at Schloss Laxenburg, near Vienna, already cited above.
Curve C represents the outlook if artificial energy production continues to grow, but at a more modest rate than in curve A, and nuclear power is not used; curve D represents an ‘optimistic’ energy strategy which keeps down the consumption of oil and coal.
Curve E illustrates the results of another strategy of decisions studied by F. Niehaus of the International Atomic Energy Agency, allowing more use of coal than curves B or D.
These curves certainly identify the increase of carbon dioxide in the atmosphere as one of the most alarming changes of the natural environment due to man and require its potential impact on the climate to be taken with the utmost seriousness.
Discussion of which of the curves in fig. 119 is likely to prove the most realistic has included the —possibly too optimistic — conception that decisions affecting the bulk of the world's energy production may come to be aimed at reducing the dangers inherent in such a drastic modification of nature.
At the other extreme, questions arise of how rapidly the world's oil and coal reserves could in fact be exploited as the portions easiest of access get used up, as well as the problems of how rapidly a switch from one type of fuel and fuel policy to another could be implemented.
The question whether the world's population will really double again also comes into it.
Birth rates are now falling in almost every country in the world (e.g. in China by 41 per cent between 1970 and 1975); and although improving availability of medical services in the Third World may be expected to lower the death rates from disease, rising death rates were in fact reported in the 1970s in a number of poorer countries — particularly in the Indian sub-continent — due to starvation following harvest failures and other natural disasters.
The energy growth situation has already begun to be affected by dawning appreciation of the squandering of limited resources, leading to price rises, and the first beginnings of the idea of strategies to reduce energy demand.
The latter ultimately entails rethinking even in architecture and clothing habits and will undoubtedly require a few decades to evolve.
At present consumption rates there will be no more fossil fuels after about AD 2200, though the enchanced CO2 in the atmosphere will be with our descendants for long after that: political decisions to reduce consumption and so spin the process out can, of course, be expected long before exhaustion of the fossil fuels is reached.
Thus the first part of the projection into the future in fig. 119 is at least on fairly firm ground in expecting less change of present growth rates than may later on be achieved.
What is clear is that the possible warming of world climates due to carbon dioxide chiefly concerns the next few centuries as the CO2 builds up and, on the present showing of human behaviour, reaches a peak with the exhaustion of fossil fuels sometime between AD 2100 and 2600.
Thereafter the atmospheric CO2 proportion is expected to decline slowly over many hundreds of years.
Theoretical modelling suggests that in AD 3500 the proportion will still be 70 per cent above the pre-industrial level.
Fig. 120 shows the range of various publicized forecasts of world temperature change based on the carbon dioxide warming effect resulting from different assumed fuel policies.
To put the prospect in perspective against the net outcome when natural climatic variations are also included, what is known in outline of the history of world temperature from the seventeenth century to date is indicated by the most widely accepted variations of five-year mean temperature level in central England and over the northern hemisphere (the latter available only since 1870).
This makes it obvious that the CO2 climate theory is not doing very well as the sole explanation of the changes and that other causes of climatic variation are also important.
The common decision to treat the natural climatic variations as unforecastable ‘noise’ (i.e. random events) is plainly not satisfactory.
Research effort must be continued, aimed at improving our capacity to foresee the variations of the natural climate.
Nevertheless, widely publicized expert opinion from the leading theoretical modelling laboratories in climatic research expects the increase of CO2 to have raised world temperature by between 1 and 2°C by the period AD 2050–2100 in the case of the most restrictive strategies on fossil fuel consumption and by from 4 to 9°C (refer to fig. 114 and text on pp. 334–6) on the basis of what are thought to be likelier developments.
These figures may even be increased by the contributions from other pollutants.
Changes of this magnitude imply bringing world temperature to a level which has not occurred in the last two million years, since the Tertiary geological period.
The polar sea ice would be expected to melt and disappear, but the great masses of inland ice covering Greenland and Antarctica would take a long time to go.
This is just as well, since melting of the Greenland ice-cap alone would raise world sea level by 6 or 7 m, while the addition of water from the Antarctic inland ice would ultimately — after a delay of some centuries as melting proceeded — raise the oceans by between 50 and 100 m, submerging lowland plains in every continent and drowning nearly all the world’s great cities.
Clearly the proposed change of world temperature level would also shift all the vegetation and crop belts poleward by many degrees of latitude, and this would take more or less immediate effect, dislocating the existing economies of nations.
Research aimed at studying the geographical distribution of expected climatic effects at each stage of the progression towards this artificial world of the twenty-first century is therefore seen as urgent.
Many exploratory studies have already been done.
Some use theoretical models of the climate system.
Others proceed by studying the climate patterns of various warm periods in the past.
These ‘scenarios’, as they are called, start with the regime in the earlier part of the present century and/or the patterns of individual warm years, a level commonly expected (on the basis discussed) to return within a decade or two.
The next stage is likened to the medieval warm epoch, with average temperature over much of the northern hemisphere around 1°C above present.
Thereafter, stages equivalent to the warmest post-glacial times, to the warmest part of the last interglacial periods, and to the late Tertiary geological epoch, are supposedly reached in succession, within at most six hundred years: the conditions of those times may therefore be relevant studies.
The general tenor of the conclusions may be summarized as follows:
1 The temperature rise over the Arctic regions generally is expected to be several times as great as the world average.
For the first doubling of the CO2 level a warming by 8–10°C near latitude 80°N is suggested.
2 With so big a change of temperature gradients, and of their position, and of that of such ice surface boundaries as would still be present, the patterns (and intensity) of the world’s wind and ocean circulations would be shifted and changed.
3 The changes of the wind and ocean circulations would alter the distribution and amounts of rain and snowfall.
The expected temperature changes have been widely announced in an ever increasing volume of meteorological literature, notably at the World Climate Conference organized by the World Meteorological Organization in February 1979 and at other scientific conferences before and since.
The alarm that has been raised over the dislocation which such great changes would be liable to cause is entirely proper, even though the actual net outcome when the natural climatic variations also have their effect (and even our view of the CO2 effect itself when the theoretical modelling has been improved) is by no means certain.
There is not very much time to acquire the necessary further knowledge to resolve this question and only too little time to adapt national and international habits and policy in the use of energy to minimize the dangers ahead — especially since some radical changes may be called for.
The dilemma is a very difficult one.
Despite the uncertain reputation of even short-term weather forecasts, and the uncertainties involved in this rather different problem, the potential for disorganization and disaster is so great that the meteorologists’ warnings must be taken as a very serious matter.
Nor is it only the temperature changes that look serious.
The changes of precipitation, and of the balance between down-put and evaporation, would also be important.
Although precipitation would be expected to increase at most latitudes because of the extra water vapour picked up from warmer seas, it is only in high latitudes and the monsoon regions of Asia that a general increase above the increased rate of evaporation would be expected.
Over most of the northern hemisphere’s land-masses conditions could turn out significantly drier than today’s.
And, as the warming should move the belts of cyclonic activity polewards, the Mediterranean winter rains would be expected to fail.
Indeed, at that latitude (35–40°N) total rainfall would probably decrease; with more evaporation there, as elsewhere, the aridity of the desert would presumably advance over the region.
The patterns that have to be considered if and when the generation of nuclear power, and the waste heat from this and from the cities of the future besides, begin to affect the climate on a global scale differ from those arising in the CO2 problem.
The artificial generation of heat is now, and presumably always will be, concentrated in limited areas.
Globally, the heat artificially generated today is only about one ten-thousandth part of the energy absorbed at the Earth’s surface from the sun.
And it seems unlikely to rise above one half of one per cent within the next century or two, possibly implying a rise of world temperature by about 1°C.
But already in some great urban and industrial areas the artificial production of heat is more than a thousand times the world average, and in certain cases exceeds locally the average heat absorbed directly from the sun.
For the possible generation of much larger amounts of heat from nuclear power production to meet future demand, the impact of heat input concentrated in various specially chosen ‘energy park regions’ in the ocean has been investigated.
This has been done by theoretical work using a ‘general circulation model’, in a collaboration between the United Kingdom Meteorological Office and the International Institute for Applied Systems Analysis (IIASA).
The possible energy parks considered were (a) just southwest of the British Isles, (b) in the region of the Cape Verde Islands near 17°N in the eastern Atlantic, and (c) east of Japan, as well as various combinations of these.
In view of inadequacies of present modelling capacity to explore interactions between atmosphere and ocean, huge inputs of heat of probably unrealistic magnitude — to supply a world population five times as big as at present and with a per capita energy consumption ten times the present average — were considered in the theoretical modelling experiments.
This was done in order to make sure of getting an identifiable response, standing out above the random variations.
It was found that there were effects on the large-scale atmospheric circulation which varied according to where the heat was put in, and how much heat, and what proportion went into the ocean and what was allowed to escape into the atmosphere.
But for the smaller heat inputs that might in fact be realized it is suggested that there might be no significant effect on the climate system.
This aspect of nuclear energy seems therefore to entail much less difficulty or danger than the carbon dioxide produced from burning traditional fuels (but, of course, this has nothing to do with the problem of radioactivity of the nuclear waste).
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
CONCLUDING SUMMARY
To conclude this chapter, we must return once again to an attempt to see the matter whole: the possibility of global warming, even drastic warming with dislocation of other elements of the climate pattern as a consequence, has to be balanced against the possibility of cooling, even drastic cooling, as the natural climate develops over the same period.
Neither side of the balance is yet adequately known and understood.
The effect of CO2 increase itself, although clear in the laboratory and in theory, is not proven as applicable in the global environment context where feedback (i.e. consequential) effects operating through the oceans and water vapour in the atmosphere may greatly alter the outcome.
Nor is the net effect of the global increase of turbidity (particulate matter) in the atmosphere as yet certain, since (a) the sizes and distribution of the suspended particles in the world atmosphere may make the difference between a net warming and a net cooling effect, and (b) in this matter also complications may arise through some of the substances facilitating the condensation of water vapour to form clouds.
All forecasts must in any case be subject to the proviso that volcanic activity does not produce so much aerosol in the atmosphere as to impose cooling, as may indeed have been happening since 1950.
So there are many reasons for scepticism about the confident forecasts based on present theoretical models, even though their warnings of what may happen must be taken so seriously as to guide policy decisions which have to be taken very early if the dangers are to be averted.
In many of his papers published in the last decade or more, Dr J. Murray Mitchell of the United States weather service, who was universally respected as one of the most cautious, as well as one of the most widely knowledgeable, research workers in this field of science, indicated that the global climate regime which we know and take for granted may be subject at this time to influences tending to push it far off course in either direction.
On the one hand, the Little Ice Age of recent centuries, which must be seen as just the latest in a series of ‘neoglacial events’, looks appreciably shorter than previous events of the series, and may not be over but only interrupted or disguised in this century, perhaps by the side-effects of man’s activity.
On the other hand, the effects of man’s activity are presumably becoming much stronger than before, but may not all tend in the same direction.
We may mention at this point that suggestions have already been made that man may be obliged in the future either to seek to avert, or slow down, the onset of a new ice age by deliberately increasing the CO2 in the atmosphere or, on the other hand, to offset the effects of his own excessive heat production by using aircraft to spread dust in the stratosphere in order to screen off the sunshine.
This latter suggestion was made by Professor M.I. Budyko in the Soviet Union as long ago as 1960.
The analysis of our present climatic situation certainly reveals basic reasons for instability of the existing climatic regime.
And in a heavily populated world where it is difficult to produce enough food, climatic instability, fluctuations and change in any direction threaten all the perils of disappointed hopes leading to conflict and, in some large areas, carry directly the threat of mass starvation.
It is vital therefore to pursue all lines of research which are likely to bring better understanding and some capacity to forecast the tendencies of both the natural climate and human impact upon it.
The instability already apparent in the climatic situation over the past twenty years has led to a position, bewildering to the public and its leaders faced with decisions affected by climate, in which the leaders of meteorological and climatic research have given conflicting advice about probable future trends.
To some extent the confusion has been due to a failure to distinguish between tendencies operating on different time-scales.
There is no necessary conflict in diagnoses which identify:
1 a cooling, especially in the northern hemisphere, since 1950 and which might be expected to continue (with shorter-term fluctuations superposed) for some decades further;
2 warming attributable to the increase of CO2and other pollutants with similar effects in the atmosphere due to human activities: this effect to become stronger over the next century or two and reach a peak around AD 2100 or some time after;
3 the progression towards the next ice age, with an expectation of some abrupt cooling phases such as to change the vegetation character in Europe and temperate North America within one to two thousand years.
Our present uncertainties about the overlaps between these tendencies do, however, frustrate forecasting attempts.
They also make it imperative to learn to identify as early as possible the signals of change when they come.
TO BE CONTINUED ...
To conclude this chapter, we must return once again to an attempt to see the matter whole: the possibility of global warming, even drastic warming with dislocation of other elements of the climate pattern as a consequence, has to be balanced against the possibility of cooling, even drastic cooling, as the natural climate develops over the same period.
Neither side of the balance is yet adequately known and understood.
The effect of CO2 increase itself, although clear in the laboratory and in theory, is not proven as applicable in the global environment context where feedback (i.e. consequential) effects operating through the oceans and water vapour in the atmosphere may greatly alter the outcome.
Nor is the net effect of the global increase of turbidity (particulate matter) in the atmosphere as yet certain, since (a) the sizes and distribution of the suspended particles in the world atmosphere may make the difference between a net warming and a net cooling effect, and (b) in this matter also complications may arise through some of the substances facilitating the condensation of water vapour to form clouds.
All forecasts must in any case be subject to the proviso that volcanic activity does not produce so much aerosol in the atmosphere as to impose cooling, as may indeed have been happening since 1950.
So there are many reasons for scepticism about the confident forecasts based on present theoretical models, even though their warnings of what may happen must be taken so seriously as to guide policy decisions which have to be taken very early if the dangers are to be averted.
In many of his papers published in the last decade or more, Dr J. Murray Mitchell of the United States weather service, who was universally respected as one of the most cautious, as well as one of the most widely knowledgeable, research workers in this field of science, indicated that the global climate regime which we know and take for granted may be subject at this time to influences tending to push it far off course in either direction.
On the one hand, the Little Ice Age of recent centuries, which must be seen as just the latest in a series of ‘neoglacial events’, looks appreciably shorter than previous events of the series, and may not be over but only interrupted or disguised in this century, perhaps by the side-effects of man’s activity.
On the other hand, the effects of man’s activity are presumably becoming much stronger than before, but may not all tend in the same direction.
We may mention at this point that suggestions have already been made that man may be obliged in the future either to seek to avert, or slow down, the onset of a new ice age by deliberately increasing the CO2 in the atmosphere or, on the other hand, to offset the effects of his own excessive heat production by using aircraft to spread dust in the stratosphere in order to screen off the sunshine.
This latter suggestion was made by Professor M.I. Budyko in the Soviet Union as long ago as 1960.
The analysis of our present climatic situation certainly reveals basic reasons for instability of the existing climatic regime.
And in a heavily populated world where it is difficult to produce enough food, climatic instability, fluctuations and change in any direction threaten all the perils of disappointed hopes leading to conflict and, in some large areas, carry directly the threat of mass starvation.
It is vital therefore to pursue all lines of research which are likely to bring better understanding and some capacity to forecast the tendencies of both the natural climate and human impact upon it.
The instability already apparent in the climatic situation over the past twenty years has led to a position, bewildering to the public and its leaders faced with decisions affected by climate, in which the leaders of meteorological and climatic research have given conflicting advice about probable future trends.
To some extent the confusion has been due to a failure to distinguish between tendencies operating on different time-scales.
There is no necessary conflict in diagnoses which identify:
1 a cooling, especially in the northern hemisphere, since 1950 and which might be expected to continue (with shorter-term fluctuations superposed) for some decades further;
2 warming attributable to the increase of CO2and other pollutants with similar effects in the atmosphere due to human activities: this effect to become stronger over the next century or two and reach a peak around AD 2100 or some time after;
3 the progression towards the next ice age, with an expectation of some abrupt cooling phases such as to change the vegetation character in Europe and temperate North America within one to two thousand years.
Our present uncertainties about the overlaps between these tendencies do, however, frustrate forecasting attempts.
They also make it imperative to learn to identify as early as possible the signals of change when they come.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
WHAT CAN WE DO ABOUT IT?
PERCEPTION AND RESPONSE
So, what can we do if the climate does fluctuate and change?
And what can we learn from the past?
To answer these questions briefly: the main requirement is realism about our situation.
We must seek to know and understand enough about the behaviour of climate and its effects upon our environment and resources to cast off illusions and false expectations.
And to be realistic also demands humility about what man can do in the face of climatic shifts, even today, other than adapt his ways.
It may well be that mankind has, and perhaps always has had, an exaggerated impression of his power to alter the climate, intentionally or otherwise, for good or ill — except on a quite local scale.
Numerous global budget calculations, covering many aspects of the atmospheric system, have been aimed in recent years at producing what are hoped to be realistic numerical estimates of the effects of human activity.
Yet our theoretical modelling is still (and may continue to be) inadequate to reveal the full power and means at nature's disposal to buffer the climate against such interference as man produces.
Nor can we be sure that the natural causes of climatic change will not overmaster the side-effects of even our enormously increasing energy production.
It is in any case among the remaining mysteries of the planet Earth which is our home — mysteries in the sense that we all find difficulty in fully fathoming and adjusting to them — that the scenery surrounding our lives is always changing.
Sometimes the changes are slow and hard to notice.
Sometimes they are fast.
Some of the changes are due to man.
Others are due to the climate and to slowly evolving successions in the natural vegetation and soils.
The rapid changes sometimes shock us and confront us with difficulties and disasters before which we still feel helpless, although modern technology has certainly enabled us to do far more than ever before in rushing aid to the scene of immediate calamity and in many cases to reduce the toll of suffering and death by short-term forewarnings issued a little before the event.
It is doubtful, however, whether we are any more capable than our forefathers of coping with long-term change — especially if it happens quickly and affects areas inhabited by millions.
Perhaps the difficulty is greatest when events come in the shape of occasional, irregularly spaced disasters — as, for instance, by drought or flood or sea storm — which give the economy time between whiles to resume its previous pattern and the population to reoccupy threatened areas.
The same human psychology that builds residential areas on active geological faults, as soon as one or two generations have lived in the area since the last great earthquake disaster, equally dulls the response of human planning to a climatic threat.
How to respond is rendered still more difficult and doubtful by uncertainties in the scientific predictions.
Yet some heed must be taken of the magnitude of the difficulties that mistaken development planning may pile up for the future.
If we decide to concentrate on what we know we have achieved and can deliver, then we must note the triumphs of our times in the reductions of loss of life attributable to coastal defences against sea flood, to hurricane and gale warnings, to highway management in frost and snow, and various forms of protection of aircraft and shipping against ice accretion, and to the interventions of medical science where water supply and hygiene are disrupted by droughts and flooding.
The successes of clean air control and legislation in industrial areas also deserve a place in the list.
The effectiveness of shelter belts and irrigation in agriculture are also beyond doubt; but with irrigation, as with coastal defences, there are obvious limits to the natural situations that can be coped with — and, perhaps, some less obvious restrictions, if unwanted or disastrous side-effects are to be avoided, as in the case of the Siberian rivers scheme discussed in earlier chapters.
Such questions demand the widest possible knowledge, understanding and caution.
The more grandiose schemes for ‘altering the face of nature’ — plans such as diversion of the Gulf Stream or the Siberian rivers or abolition of the Arctic ice — should be approached not only with caution but with scepticism.
As long as our capacity for forecasting the weather is limited and sometimes marred by gross errors affecting large areas, our ability to foresee the consequences of any deliberate manipulation of the climate system that might be attempted must be subject to the same danger.
Our world economy is geared to the existing climate, and any major change — even one aimed at increasing the overall cultivable area — would entail grave dislocation, quite apart from the likely short-term vagaries of weather and failures of forecast that would have to be expected, let alone the possibility of long-term deviations from the result planned.
These could obviously affect some areas and even whole countries adversely.
And it seems certain that fully international agreement to accept the hazards involved could never be obtained.
There is already a demand — and a need — for international agreements on a modest and surely attainable scale to control and avoid activities which might have, or in some cases are known to have, adverse effects on environment and climate.
Cases in point range from the emission of sulphurous gases from chimneys to the unlimited use of aerosol sprays and nitrogen fertilizers.
And it is clear that national and international policy with regard to future fuel development, which involves great unsolved problems ranging from the effect of increasing carbon dioxide and waste heat output to the disposal of nuclear residues, demands a continuing search for knowledge and, in the meantime, caution and flexibility.
Turning once more to matters within our present capabilities, Walter Orr Roberts and Henry Lansford have made the valid point that in the absence of forecasts or outlooks precise enough to satisfy a meteorologist, the farmer is likely to make some hard and important decisions on the basis of intelligent guesses … about future weather and climate that fall far short of the atmospheric scientist's rigorous standards of acceptability.
For example, every dryland farmer in the high plains [of the United States] probably knows by now that severe drought has struck the region about every 20 to 22 years for the last 160 years….
Even conjectures can be of some use in making climate–related decisions in the real world, provided they are not completely wild.
TO BE CONTINUED ...
PERCEPTION AND RESPONSE
So, what can we do if the climate does fluctuate and change?
And what can we learn from the past?
To answer these questions briefly: the main requirement is realism about our situation.
We must seek to know and understand enough about the behaviour of climate and its effects upon our environment and resources to cast off illusions and false expectations.
And to be realistic also demands humility about what man can do in the face of climatic shifts, even today, other than adapt his ways.
It may well be that mankind has, and perhaps always has had, an exaggerated impression of his power to alter the climate, intentionally or otherwise, for good or ill — except on a quite local scale.
Numerous global budget calculations, covering many aspects of the atmospheric system, have been aimed in recent years at producing what are hoped to be realistic numerical estimates of the effects of human activity.
Yet our theoretical modelling is still (and may continue to be) inadequate to reveal the full power and means at nature's disposal to buffer the climate against such interference as man produces.
Nor can we be sure that the natural causes of climatic change will not overmaster the side-effects of even our enormously increasing energy production.
It is in any case among the remaining mysteries of the planet Earth which is our home — mysteries in the sense that we all find difficulty in fully fathoming and adjusting to them — that the scenery surrounding our lives is always changing.
Sometimes the changes are slow and hard to notice.
Sometimes they are fast.
Some of the changes are due to man.
Others are due to the climate and to slowly evolving successions in the natural vegetation and soils.
The rapid changes sometimes shock us and confront us with difficulties and disasters before which we still feel helpless, although modern technology has certainly enabled us to do far more than ever before in rushing aid to the scene of immediate calamity and in many cases to reduce the toll of suffering and death by short-term forewarnings issued a little before the event.
It is doubtful, however, whether we are any more capable than our forefathers of coping with long-term change — especially if it happens quickly and affects areas inhabited by millions.
Perhaps the difficulty is greatest when events come in the shape of occasional, irregularly spaced disasters — as, for instance, by drought or flood or sea storm — which give the economy time between whiles to resume its previous pattern and the population to reoccupy threatened areas.
The same human psychology that builds residential areas on active geological faults, as soon as one or two generations have lived in the area since the last great earthquake disaster, equally dulls the response of human planning to a climatic threat.
How to respond is rendered still more difficult and doubtful by uncertainties in the scientific predictions.
Yet some heed must be taken of the magnitude of the difficulties that mistaken development planning may pile up for the future.
If we decide to concentrate on what we know we have achieved and can deliver, then we must note the triumphs of our times in the reductions of loss of life attributable to coastal defences against sea flood, to hurricane and gale warnings, to highway management in frost and snow, and various forms of protection of aircraft and shipping against ice accretion, and to the interventions of medical science where water supply and hygiene are disrupted by droughts and flooding.
The successes of clean air control and legislation in industrial areas also deserve a place in the list.
The effectiveness of shelter belts and irrigation in agriculture are also beyond doubt; but with irrigation, as with coastal defences, there are obvious limits to the natural situations that can be coped with — and, perhaps, some less obvious restrictions, if unwanted or disastrous side-effects are to be avoided, as in the case of the Siberian rivers scheme discussed in earlier chapters.
Such questions demand the widest possible knowledge, understanding and caution.
The more grandiose schemes for ‘altering the face of nature’ — plans such as diversion of the Gulf Stream or the Siberian rivers or abolition of the Arctic ice — should be approached not only with caution but with scepticism.
As long as our capacity for forecasting the weather is limited and sometimes marred by gross errors affecting large areas, our ability to foresee the consequences of any deliberate manipulation of the climate system that might be attempted must be subject to the same danger.
Our world economy is geared to the existing climate, and any major change — even one aimed at increasing the overall cultivable area — would entail grave dislocation, quite apart from the likely short-term vagaries of weather and failures of forecast that would have to be expected, let alone the possibility of long-term deviations from the result planned.
These could obviously affect some areas and even whole countries adversely.
And it seems certain that fully international agreement to accept the hazards involved could never be obtained.
There is already a demand — and a need — for international agreements on a modest and surely attainable scale to control and avoid activities which might have, or in some cases are known to have, adverse effects on environment and climate.
Cases in point range from the emission of sulphurous gases from chimneys to the unlimited use of aerosol sprays and nitrogen fertilizers.
And it is clear that national and international policy with regard to future fuel development, which involves great unsolved problems ranging from the effect of increasing carbon dioxide and waste heat output to the disposal of nuclear residues, demands a continuing search for knowledge and, in the meantime, caution and flexibility.
Turning once more to matters within our present capabilities, Walter Orr Roberts and Henry Lansford have made the valid point that in the absence of forecasts or outlooks precise enough to satisfy a meteorologist, the farmer is likely to make some hard and important decisions on the basis of intelligent guesses … about future weather and climate that fall far short of the atmospheric scientist's rigorous standards of acceptability.
For example, every dryland farmer in the high plains [of the United States] probably knows by now that severe drought has struck the region about every 20 to 22 years for the last 160 years….
Even conjectures can be of some use in making climate–related decisions in the real world, provided they are not completely wild.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
APPROACHES TO CLIMATE FORECASTING AND THEIR USEFULNESS
Another point which should already affect decisions today comes from studies of the aftermath of the world-wide stresses of the early-mid-1970s by Michael Glantz.
Officials of the governments and others concerned in the countries in the Sahel were asked what they would have done if a reliable climate forecast had been available before the worst phase of the Sahel drought around 1972–3.
A common answer was that the cattle-carrying capacity of the rangelands should have been assessed and cattle-herders required to keep down the size of their herds to prevent overgrazing.
A policy of culling the herds to improve them by keeping only the best beasts could have been enjoined upon the owners at the same time.
There has also been already a more general pay-off from the increased activity in climate research over the last ten to twenty years in an awareness — however little acted upon so far — that climate is not as constant as it appeared to be in the most benign decades of the present century.
Even the most extreme and divergent forecasts of future climate, put forward in this period prematurely by scientists who were expert in only this or that part of the enormously wide fields of relevant knowledge, may have done some good by undermining complacency and alerting the world community to what can happen.
Nevertheless, this is a situation which cannot be allowed to continue.
The daunted decision-makers, who must have been confused and disillusioned about the value of ‘experts’, should perhaps see it as a stage that had to be gone through after the long neglect of investigation of the history and development of climate.
The need is for research to improve knowledge and, particularly, to understand the limitations of each kind of approach to forecasting.
And for the planners the lesson already is to allow somewhat wider margins for the possibility of climatic change.
There are two main problems, to extend our knowledge of (a) the behaviour of the natural climate, and (b) the effects of the intrusion of human activities and pollutants, both those now occurring and those implied as the situation is planned to develop, or may develop, in the future.
There are also two lines of advance needed:
1 To reconstruct an ever fuller and more extensive past record of the global climate.
This is the essential observation base of climatology, without which some of the processes and phenomena we have to deal with in forecasting may remain undiscovered and our theoretical concepts and models may remain incomplete and untested.
2 To achieve fuller understanding of the controls and mechanisms of climatic behaviour, and their range of variation, by physical and mathematical climate theory.
The theoretical models may be of various kinds.
Their range includes physical models such as experiments with fluids in rotating dishpans, simulating in a simplified way the flow of the atmosphere when the heating is varied; and it extends through mathematical models from quite simple ones, which express only the mean state of the atmosphere and oceans and explore the balance of energy received and heat transported by the winds and ocean currents, to the most elaborate models of the general wind circulation (as used in numerical daily weather forecasting).
Either type of model may also be used to consider the budgets of heat, momentum and water vapour transfer.
The simplest models may be designed to consider only the situation averaged around the world for each latitude.
The most elaborate models offer some insight into regional patterns and make it possible to consider the effects of mountain or hill barriers and other local disturbances upon the winds, all necessarily simulated in simplified form.
All models need calibrating and testing by comparisons with results observed in the real world.
The climatic situations reconstructed from the past, provided the job has been reliably done, are needed also by the theoretical modeller.
General circulation models are conventionally ‘run’ — i.e. integration of the equations is continued, as if for forecasting — for periods of eighty days to at most (on grounds of cost) a year or two.
The maps produced for this period are then used to provide a statistical picture of the ‘climate’ — for example, maps of the frequency of anticyclones and depressions, of rainfall and different wind directions — of the period covered.
This theoretical climate can be compared with the observed climate of any epoch which it was intended to simulate.
The effects of altering the ground conditions and heating pattern, or of putting more or less water vapour and other substances into the air, and other changes, can be similarly explored.
By repeating runs of the model, from slightly different starting conditions specified for day zero, an idea of the stability of the statistics derived from the runs to represent a given climatic regime can be derived — or, to put this another way, one is enabled to see how big a random element there is in the result.
So far the models do not incorporate fully the exchanges with the ocean, and effects within the ocean, and how these react upon the atmosphere.
A more serious uncertainty affects the theoretical results.
This is because the complexity of the climate system, the more fully and elegantly it is represented, provides opportunities at so many points to adjust this or that component and obtain at least some sort of match with the climatic regime to be explained.
This is a matter of giving more weight to this or that and making compensatory adjustments elsewhere.
As Schneider put it in the case described in chapter 16 (pp. 339–40), one can match anything to any-thing in this way, but the question of whether the set-up then expressed by the equations corresponds to the mechanisms of the real climate regime remains open.
(There may even be a variety of hypothetical (modelled) set-ups by which the characteristics of the actual regime could be reproduced.)
Modelling in a realm as complex, and with as many interactive variables, as the climatic system is primarily an aid to thought and to conceiving the patterns of the real world rather than an automatic provider of accurate or reliable answers.
It can suggest probable linkages of cause and effect in the climate system and often the probable order of magnitude of some of the effects.
And it is obviously the main way of exploring the possible consequences of human activities which introduce new elements or changed conditions into the climate system, whether by pollutants in the air or extra heat or alterations of the face of the Earth — as in the creation of artificial lakes or clearing of the tropical rain-forests (and proposals like removal of the Arctic sea ice).
Two quite different types of forecast, whether for a season ahead or of the climate in the longer term, can also be attempted.
One is specific, stating that the prevailing weather will be warmer, or colder, or perhaps even specifying a temperature range (and correspondingly for rainfall).
The forecasts of carbon dioxide warming, and of the next ice age some thousands of years ahead, are in this category.
(This seems also to be the style preferred for all occasions by amateurs and quacks.)
The other type of forecast takes the form of a statistical statement of the probability of this or that range of conditions.
The modelling approach can be used to produce forecasts in either form.
Forecasts based on analysis of the past record of climate can logically only be made in the statistical type of statement of the probability of certain outcomes following the known initial conditions.
It is arguable that the statistical form of statement is most helpful to the recipient, especially when great risks (economic risks or human lives and sufferings) depend upon the decisions he has to make.
But the statement of probabilities only has meaning in relation to the range of thinking, of items known to be relevant, and of the reference material surveyed, in making the forecast.
Those items which constitute the basis of the probability statement must be made clear to the recipient: for without them the alleged probability is no more than a guess, which the recipient cannot evaluate, and which may be quite unrelated to the realities of the situation.
It seems highly desirable that forecasts based on insight gained from modelling studies should also be produced as statistical statements of probabilities which are similarly made understandable — i.e. assessable — to the recipient.
In the present state of knowledge the basically empirical approach to forecasting resting on the past record of climate will commend itself to most recipients.
The probabilities of various future developments of the natural climate can be clearly and explicitly assessed on this basis by consideration of suitable numbers of previous occurrences of an apparently similar climatic situation and what followed in those cases.
The contribution of theoretical modelling can best come in by illuminating whether and in what ways the previous occurrences were really similar to the existing situation.
In the case of any new climatic trend or developments which may result from man's activities, however, theoretical modelling may be the only way of predicting the outcome and its probable order of magnitude, apart from such additional information as may be gleaned from study of seemingly relevant ‘scenarios’ chosen from climates which did occur in the past.
In connection with the possibility of drastic warming resulting from the prospective further increase of carbon dioxide, comparative studies have been made of the world climate patterns of the warmest of past interglacials and the still warmer climates of the Tertiary geological period (more than two million years ago), as a guide to the patterns of warmth and rainfall which might arise and dislocate the economy of the world as we know it.
TO BE CONTINUED ...
Another point which should already affect decisions today comes from studies of the aftermath of the world-wide stresses of the early-mid-1970s by Michael Glantz.
Officials of the governments and others concerned in the countries in the Sahel were asked what they would have done if a reliable climate forecast had been available before the worst phase of the Sahel drought around 1972–3.
A common answer was that the cattle-carrying capacity of the rangelands should have been assessed and cattle-herders required to keep down the size of their herds to prevent overgrazing.
A policy of culling the herds to improve them by keeping only the best beasts could have been enjoined upon the owners at the same time.
There has also been already a more general pay-off from the increased activity in climate research over the last ten to twenty years in an awareness — however little acted upon so far — that climate is not as constant as it appeared to be in the most benign decades of the present century.
Even the most extreme and divergent forecasts of future climate, put forward in this period prematurely by scientists who were expert in only this or that part of the enormously wide fields of relevant knowledge, may have done some good by undermining complacency and alerting the world community to what can happen.
Nevertheless, this is a situation which cannot be allowed to continue.
The daunted decision-makers, who must have been confused and disillusioned about the value of ‘experts’, should perhaps see it as a stage that had to be gone through after the long neglect of investigation of the history and development of climate.
The need is for research to improve knowledge and, particularly, to understand the limitations of each kind of approach to forecasting.
And for the planners the lesson already is to allow somewhat wider margins for the possibility of climatic change.
There are two main problems, to extend our knowledge of (a) the behaviour of the natural climate, and (b) the effects of the intrusion of human activities and pollutants, both those now occurring and those implied as the situation is planned to develop, or may develop, in the future.
There are also two lines of advance needed:
1 To reconstruct an ever fuller and more extensive past record of the global climate.
This is the essential observation base of climatology, without which some of the processes and phenomena we have to deal with in forecasting may remain undiscovered and our theoretical concepts and models may remain incomplete and untested.
2 To achieve fuller understanding of the controls and mechanisms of climatic behaviour, and their range of variation, by physical and mathematical climate theory.
The theoretical models may be of various kinds.
Their range includes physical models such as experiments with fluids in rotating dishpans, simulating in a simplified way the flow of the atmosphere when the heating is varied; and it extends through mathematical models from quite simple ones, which express only the mean state of the atmosphere and oceans and explore the balance of energy received and heat transported by the winds and ocean currents, to the most elaborate models of the general wind circulation (as used in numerical daily weather forecasting).
Either type of model may also be used to consider the budgets of heat, momentum and water vapour transfer.
The simplest models may be designed to consider only the situation averaged around the world for each latitude.
The most elaborate models offer some insight into regional patterns and make it possible to consider the effects of mountain or hill barriers and other local disturbances upon the winds, all necessarily simulated in simplified form.
All models need calibrating and testing by comparisons with results observed in the real world.
The climatic situations reconstructed from the past, provided the job has been reliably done, are needed also by the theoretical modeller.
General circulation models are conventionally ‘run’ — i.e. integration of the equations is continued, as if for forecasting — for periods of eighty days to at most (on grounds of cost) a year or two.
The maps produced for this period are then used to provide a statistical picture of the ‘climate’ — for example, maps of the frequency of anticyclones and depressions, of rainfall and different wind directions — of the period covered.
This theoretical climate can be compared with the observed climate of any epoch which it was intended to simulate.
The effects of altering the ground conditions and heating pattern, or of putting more or less water vapour and other substances into the air, and other changes, can be similarly explored.
By repeating runs of the model, from slightly different starting conditions specified for day zero, an idea of the stability of the statistics derived from the runs to represent a given climatic regime can be derived — or, to put this another way, one is enabled to see how big a random element there is in the result.
So far the models do not incorporate fully the exchanges with the ocean, and effects within the ocean, and how these react upon the atmosphere.
A more serious uncertainty affects the theoretical results.
This is because the complexity of the climate system, the more fully and elegantly it is represented, provides opportunities at so many points to adjust this or that component and obtain at least some sort of match with the climatic regime to be explained.
This is a matter of giving more weight to this or that and making compensatory adjustments elsewhere.
As Schneider put it in the case described in chapter 16 (pp. 339–40), one can match anything to any-thing in this way, but the question of whether the set-up then expressed by the equations corresponds to the mechanisms of the real climate regime remains open.
(There may even be a variety of hypothetical (modelled) set-ups by which the characteristics of the actual regime could be reproduced.)
Modelling in a realm as complex, and with as many interactive variables, as the climatic system is primarily an aid to thought and to conceiving the patterns of the real world rather than an automatic provider of accurate or reliable answers.
It can suggest probable linkages of cause and effect in the climate system and often the probable order of magnitude of some of the effects.
And it is obviously the main way of exploring the possible consequences of human activities which introduce new elements or changed conditions into the climate system, whether by pollutants in the air or extra heat or alterations of the face of the Earth — as in the creation of artificial lakes or clearing of the tropical rain-forests (and proposals like removal of the Arctic sea ice).
Two quite different types of forecast, whether for a season ahead or of the climate in the longer term, can also be attempted.
One is specific, stating that the prevailing weather will be warmer, or colder, or perhaps even specifying a temperature range (and correspondingly for rainfall).
The forecasts of carbon dioxide warming, and of the next ice age some thousands of years ahead, are in this category.
(This seems also to be the style preferred for all occasions by amateurs and quacks.)
The other type of forecast takes the form of a statistical statement of the probability of this or that range of conditions.
The modelling approach can be used to produce forecasts in either form.
Forecasts based on analysis of the past record of climate can logically only be made in the statistical type of statement of the probability of certain outcomes following the known initial conditions.
It is arguable that the statistical form of statement is most helpful to the recipient, especially when great risks (economic risks or human lives and sufferings) depend upon the decisions he has to make.
But the statement of probabilities only has meaning in relation to the range of thinking, of items known to be relevant, and of the reference material surveyed, in making the forecast.
Those items which constitute the basis of the probability statement must be made clear to the recipient: for without them the alleged probability is no more than a guess, which the recipient cannot evaluate, and which may be quite unrelated to the realities of the situation.
It seems highly desirable that forecasts based on insight gained from modelling studies should also be produced as statistical statements of probabilities which are similarly made understandable — i.e. assessable — to the recipient.
In the present state of knowledge the basically empirical approach to forecasting resting on the past record of climate will commend itself to most recipients.
The probabilities of various future developments of the natural climate can be clearly and explicitly assessed on this basis by consideration of suitable numbers of previous occurrences of an apparently similar climatic situation and what followed in those cases.
The contribution of theoretical modelling can best come in by illuminating whether and in what ways the previous occurrences were really similar to the existing situation.
In the case of any new climatic trend or developments which may result from man's activities, however, theoretical modelling may be the only way of predicting the outcome and its probable order of magnitude, apart from such additional information as may be gleaned from study of seemingly relevant ‘scenarios’ chosen from climates which did occur in the past.
In connection with the possibility of drastic warming resulting from the prospective further increase of carbon dioxide, comparative studies have been made of the world climate patterns of the warmest of past interglacials and the still warmer climates of the Tertiary geological period (more than two million years ago), as a guide to the patterns of warmth and rainfall which might arise and dislocate the economy of the world as we know it.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
INTERNATIONAL EFFORTS NEEDED TO IMPROVE KNOWLEDGE
While our knowledge of climate development processes remains far from complete, the immediate needs are that research continue and that a running watch be kept on the state of world climate.
In the latter connection, identification of a few items (e.g. the Arctic temperatures, and extent of sea ice, or perhaps the occurrence of the westerly winds near the British Isles, as discussed in chapter 14) which could serve as a quickly responding, economical index of world climate may be of value.
But in relation to the vulnerability of our economy and international arrangements to climatic changes, the bald assertion in a recent British government report that no big natural changes are likely soon has no value at all.
And the corresponding assertion of one leading scientist that it is a waste of money now to support any research into climatic change other than changes likely to be produced by man's impact is equally without foundation and likely to lead to a vital element of the problem being overlooked.
In fact, the increasing concern in recent years over climatic change led to the inauguration in 1979 of an international programme of climatic research under the World Meteorological Organization, known as the World Climate Programme, and national programmes in several countries (e.g. in the United States and in the European Community).
It seems unfortunate that, according to report, the Climate Impacts Assessment side proposed for the World Climate Programme was left to be taken care of by the United Nations Environment Programme.
Studies of how to reduce the vulnerability of our food supply systems to climatic variability must be one of the most vital practical problems confronting mankind, affecting the whole economy.
It has been pointed out also that some schemes, successful or otherwise, to modify the climate or the environment of certain areas — as, for example, diversion of the Siberian rivers for irrigation in central Asia, with possibly serious repercussions through diminishing the Arctic sea ice, or the seeding of clouds in many areas to extract rain from them — may have damaging effects on the climate and economic interests of other countries beyond the borders of the region concerned.
As populations and demands on resources continue to increase, governments will be under mounting domestic pressure to put national requirements first….
If the world is not to relapse into anarchy, with states warring over use and abuse of natural resources, some sort of international agreement … a self-denying ordinance and commitment to consult will be essential.
The author of these sentences, C.Tickell, formerly of the Office of the President of the European Community, goes on to suggest that an international organization — a World Climate Organization, perhaps — will be needed to monitor and take appropriate action on such matters.
There is no doubt that all the problems of adaptation to climatic fluctuations and change are made harder by the high level and continuing increase of world population.
In an interesting article in the Yale Review (vol. 64, pp. 357–69, 1975) on ‘An Ecologist’s View of History’, Paul Colinvaux has argued that all poverty (on a mass scale) in every age is caused by the continued growth of population and that behind all the great aggressive conquests of history will be found a rising population who have seen for a while hopes of a rising standard of life.
He believes that the ‘brooding about the possibilities of nuclear war’ between the great continental states which are the superpowers of today may be misplaced, that the real threat comes from island peoples or other nations with teeming populations living in a confined space and with an aggressive nature evidenced in their history.
He sees hope for the future in the likelihood that technology can continue to find raw materials and even energy for manufacturing almost without limit.
But he remarks that, even so, we are clearly going to force people to live in uncongenial ways, with rationing of space and few outlets for adventure: ‘for a time at least we are going to deny them the right to aggressive war’.
Parts of this case may be plainly overstated, but its main themes are assuredly partly true.
What the statement does not include is that the pressure towards such an outlook for mankind will be further intensified by any reduction of resources and living space such as climatic fluctuations and change are liable to bring at least temporarily and in some cases for the longer term.
TO BE CONTINUED ...
While our knowledge of climate development processes remains far from complete, the immediate needs are that research continue and that a running watch be kept on the state of world climate.
In the latter connection, identification of a few items (e.g. the Arctic temperatures, and extent of sea ice, or perhaps the occurrence of the westerly winds near the British Isles, as discussed in chapter 14) which could serve as a quickly responding, economical index of world climate may be of value.
But in relation to the vulnerability of our economy and international arrangements to climatic changes, the bald assertion in a recent British government report that no big natural changes are likely soon has no value at all.
And the corresponding assertion of one leading scientist that it is a waste of money now to support any research into climatic change other than changes likely to be produced by man's impact is equally without foundation and likely to lead to a vital element of the problem being overlooked.
In fact, the increasing concern in recent years over climatic change led to the inauguration in 1979 of an international programme of climatic research under the World Meteorological Organization, known as the World Climate Programme, and national programmes in several countries (e.g. in the United States and in the European Community).
It seems unfortunate that, according to report, the Climate Impacts Assessment side proposed for the World Climate Programme was left to be taken care of by the United Nations Environment Programme.
Studies of how to reduce the vulnerability of our food supply systems to climatic variability must be one of the most vital practical problems confronting mankind, affecting the whole economy.
It has been pointed out also that some schemes, successful or otherwise, to modify the climate or the environment of certain areas — as, for example, diversion of the Siberian rivers for irrigation in central Asia, with possibly serious repercussions through diminishing the Arctic sea ice, or the seeding of clouds in many areas to extract rain from them — may have damaging effects on the climate and economic interests of other countries beyond the borders of the region concerned.
As populations and demands on resources continue to increase, governments will be under mounting domestic pressure to put national requirements first….
If the world is not to relapse into anarchy, with states warring over use and abuse of natural resources, some sort of international agreement … a self-denying ordinance and commitment to consult will be essential.
The author of these sentences, C.Tickell, formerly of the Office of the President of the European Community, goes on to suggest that an international organization — a World Climate Organization, perhaps — will be needed to monitor and take appropriate action on such matters.
There is no doubt that all the problems of adaptation to climatic fluctuations and change are made harder by the high level and continuing increase of world population.
In an interesting article in the Yale Review (vol. 64, pp. 357–69, 1975) on ‘An Ecologist’s View of History’, Paul Colinvaux has argued that all poverty (on a mass scale) in every age is caused by the continued growth of population and that behind all the great aggressive conquests of history will be found a rising population who have seen for a while hopes of a rising standard of life.
He believes that the ‘brooding about the possibilities of nuclear war’ between the great continental states which are the superpowers of today may be misplaced, that the real threat comes from island peoples or other nations with teeming populations living in a confined space and with an aggressive nature evidenced in their history.
He sees hope for the future in the likelihood that technology can continue to find raw materials and even energy for manufacturing almost without limit.
But he remarks that, even so, we are clearly going to force people to live in uncongenial ways, with rationing of space and few outlets for adventure: ‘for a time at least we are going to deny them the right to aggressive war’.
Parts of this case may be plainly overstated, but its main themes are assuredly partly true.
What the statement does not include is that the pressure towards such an outlook for mankind will be further intensified by any reduction of resources and living space such as climatic fluctuations and change are liable to bring at least temporarily and in some cases for the longer term.
TO BE CONTINUED ...
Re: CLIMATE, HISTORY AND THE MODERN WORLD
THE LESSONS OF HISTORY
In the preparations for the World Climate Conference in 1979 Professor B. Bolin of the University of Stockholm suggested the following points as common ground, namely that:
1 the variability of climate, as experienced during the last few centuries, has had a marked effect on man’s activities and well-being;
2 the variability of the natural climate will continue during the next hundred years…and that there is some possibility that a more extreme and probably cooler climate, as during the seventeenth to nineteeth centuries, may develop;
3 man is already influencing climate on a local scale to an extent which is significant when compared with the natural variability of climate;
4 man’s activities may come during the next hundred years to induce global climatic changes as great as, or even significantly larger than, the climatic changes experienced in the last few centuries;
5 the effects of man’s activities will probably be to produce a warmer climate and significant changes of the world rainfall pattern;
6 for mankind to adapt better in the future to the variability of climate, even to bigger changes than those experienced in the recent historical past, will demand more effective use of climatic data and continued research effort to improve our capability of forecasting.
No doubt some will regard these anxieties about climate as the least of our worries in a world troubled by sharply rising energy costs and concentrations of wealth in oil-producing states, by increasing violence everywhere and the threat of nuclear war.
After all, the climate does not seem to have changed, many will say.
And anyway we have always had to cope with climatic extremes from time to time.
But this is to overlook the inbuilt trap in the nature of the climate problem, that the wide range of year-to-year variations will always make it hard to recognize any new trend until this is already strongly established.
It is true that in some recent years India has been able to spare some food for export.
But the increasing population pressure on food resources increases vulnerability to even one bad year.
In the midst of the better-known symptoms of tension, it may be overlooked that already in the 1970s, even in the United States, with increased acreage sown, yields of grain per acre dropped sharply and that monsoon failures in India and Bangladesh twice in the early and mid-1970s seem to have caused over a million deaths.
And should we see in the tragedy of the emigration of the ‘boat people’ (with countless drownings) from southeast Asia in the late 1970s a (possibly not new) twist in the problem of food shortages, caused by weather as well as the ravages of war, whereby political prejudices choose the victims, the classes of the population on whom the main brunt falls.
This is close to one of the lessons of history, that in troubled times and periods of scarcity scapegoats are usually found — and often illogically chosen — to take the blame and become the targets of vengeful acts, of riots and war, or else that it is merely the weakest sections of society — the poor, the old and the children—who are made to suffer the worst consequences.
TO BE CONTINUED ...
In the preparations for the World Climate Conference in 1979 Professor B. Bolin of the University of Stockholm suggested the following points as common ground, namely that:
1 the variability of climate, as experienced during the last few centuries, has had a marked effect on man’s activities and well-being;
2 the variability of the natural climate will continue during the next hundred years…and that there is some possibility that a more extreme and probably cooler climate, as during the seventeenth to nineteeth centuries, may develop;
3 man is already influencing climate on a local scale to an extent which is significant when compared with the natural variability of climate;
4 man’s activities may come during the next hundred years to induce global climatic changes as great as, or even significantly larger than, the climatic changes experienced in the last few centuries;
5 the effects of man’s activities will probably be to produce a warmer climate and significant changes of the world rainfall pattern;
6 for mankind to adapt better in the future to the variability of climate, even to bigger changes than those experienced in the recent historical past, will demand more effective use of climatic data and continued research effort to improve our capability of forecasting.
No doubt some will regard these anxieties about climate as the least of our worries in a world troubled by sharply rising energy costs and concentrations of wealth in oil-producing states, by increasing violence everywhere and the threat of nuclear war.
After all, the climate does not seem to have changed, many will say.
And anyway we have always had to cope with climatic extremes from time to time.
But this is to overlook the inbuilt trap in the nature of the climate problem, that the wide range of year-to-year variations will always make it hard to recognize any new trend until this is already strongly established.
It is true that in some recent years India has been able to spare some food for export.
But the increasing population pressure on food resources increases vulnerability to even one bad year.
In the midst of the better-known symptoms of tension, it may be overlooked that already in the 1970s, even in the United States, with increased acreage sown, yields of grain per acre dropped sharply and that monsoon failures in India and Bangladesh twice in the early and mid-1970s seem to have caused over a million deaths.
And should we see in the tragedy of the emigration of the ‘boat people’ (with countless drownings) from southeast Asia in the late 1970s a (possibly not new) twist in the problem of food shortages, caused by weather as well as the ravages of war, whereby political prejudices choose the victims, the classes of the population on whom the main brunt falls.
This is close to one of the lessons of history, that in troubled times and periods of scarcity scapegoats are usually found — and often illogically chosen — to take the blame and become the targets of vengeful acts, of riots and war, or else that it is merely the weakest sections of society — the poor, the old and the children—who are made to suffer the worst consequences.
TO BE CONTINUED ...