The problem of global warming caused by an excessive concentration of carbon dioxide in the atmosphere is one of the challenges of our age. Now how does it affect natural conditions in Russia and in neighboring countries? Reconstructing the climates and landscapes of the dim and distant past - when mean air temperatures were rising by a value close to one anticipated in this new century - may help us get some of the answers.
by Andrei VELICHKO, Dr. Sc. (Geogr.), Institute of Geography, Russian Academy of Sciences
DIFFERENT LEVELS OF WARMING-DIFFERENT CLIMATE
The mean global temperature is likely to rise by 0.7 to 1 0 C in the first half of the 21st century, and by 1.7 to 2 0 C in its latter half. Such are the estimates of the Intergovernmental Group on Climate. Research scientists of the Evolutionary Laboratory of our Institute agree with this verdict on the basis of their own findings. The predicted temperature rises are consistent with their paleoclimatic reconstructions for optima (warmest epochs) of the Contemporary Interglacial, when the mean global temperature was rising by 0.6 to 1 0 C; they are also consistent with the preceding Mikulino Interglacial (which occurred 70 to 110 thousand years ago), when the temperature increase amounted to 1.6 to 2 0 C above the present-day values.
In either case the greatest warming affected the high-latitude territories, though the total area was twice as large during the Mikulino Interglacial. In the belt between 45 0 and 35 0 N temperature rises were lower, while further south the temperature pattern was characterized by an alternation of low- positive and low-negative deviations. But whereas temperature changes in both cases concurred by and large, the amount of annual precipitation showed substantial differences, especially in what are now the arid and semi-arid regions. A 1 0 C rise in the mean global temperature was accompanied by the appearance of vast regions where the precipitation level showed a dramatic downturn. These regions formed, as it were, a broken circumpolar belt, with the center at the point of the pole. But if a temperature rise was up to 2 0 C, such regions disappeared. In high latitudes both thermal regimes contributed to a higher level of moisture, and in low latitudes, too, this process was more active than today.
It is remarkable that in the amount of precipitation at different latitudes the situation in the second thermal regime was opposite to what we are having now: in the optimum of the Mikulino Interglacial, boreal (northern) expanses went dry, while in arid regions the humidity level increased substantially.
The above two-level climatic characteristics determined the specifics of the general pattern of air circulation in the atmosphere. Special studies with the use of digital simulation methods are imperative so as to reconstitute the air circulation systems of the distant past. At this point it would be enough if we call attention to some of the climatic parameters of those epochs. For instance, the distribution of temperatures over latitude belts attests to a decrease of their meridional gradient from the equator to the pole compared with the modem times. And yet the zone of enhanced humidity in Eurasia's boreal belt went farther east into Siberia than today This phenomenon is thought to be caused by the predominant pattern of air movement in the Northern Hemisphere from west to east. However, the decrease in the meridional temperature gradient in no way agrees with this assumption. Possibly the scenario was different: cyclones that carried precipitation from the Atlantic eastwards were due to a land warming differential - dry land warmed up more in summer and less in winter. The shrinking areas of the Siberian and Central Asian anticyclones must have also contributed to the advance of a mass of humid air from the Atlantic further east. But in low attitudes the increase in the amount of precipitation might have been related to activation of the monsoon system of circulation in regions with higher summer temperatures.
Besides the climatic reconstructions for those epochs, we have also obtained data on the condition of the environment. In particular, we have drawn maps of landscape components. These data are but a reference point, no more, in identification of anticipated changes of the climate. Special approaches had to be developed for more realistic assessments.
This area of research - a response of geosystems to dramatic changes in temperature and humidity levels that occur just within a few decades - is an utterly new trend in a geographer's prognostic studies. But it became possible already at the initial stage to detect some of the characteristics of these natural complexes- characteristics essential for predicting the true values of the imminent climatic changes. These are above all the inertial characteristics of geosystems, or a lag in their response to a newly emerged climatic situation. Another characteristic is what we call poly-chronicity; this means that each component of a geosystem needs a definite
time specific to it for transformation and adjustment to new conditions. For example, for sea lions the adjustment response may take one or several years. But this period is much longer for upper soil in areas of perpetually frozen ground during seasonal thawings; it takes dozens of years and even centuries for the plant cover to develop any appreciable changes. And even a longer period for the mantle of soil and for relief (topography).
Thus different components of a geosystem show a different pace of response. The very combination of such disparate responses exerts a significant effect on the set of its biochemical cycles. Furthermore, certain individual parts within each component likewise have a wide range of transformation periods toward readjustment. For instance, the transformation of topography of a particular region takes hundreds of years, and individual relief features need different periods for that too. So, the pattern is quite multivariant. Even when considering erosion processes (those on the slopes of mountains and hills too), we confront a variety of periods - from one year (landslips, small ruts or grooves) to many centuries and even millennia (formation of valley terraces).
Vegetation, too, shows a diversity of such characteristic periods. Their spectrum comprises the time of response of individual plants to climatic changes, of plant communities and the like.
Such spectra of characteristic periods - as well as their components and subcomponents - are individual for each particular region. Only when we know all that will it become possible to get down to the most important operation, that is the conjugate analysis of the characteristics obtained. Thereby we shall be able to tackle the next stage of our research, the synthesis of a geosystem's behavior under new climatic conditions through designing a model of what we call a non-equilibrium model of a geosystem's reaction to changing conditions. Different landscape components, each having a different characteristic time of adaptation, cannot adjust in full to new conditions within a short period of several decades. As a result, the balanced interaction of such components will be upset, and our geosystem will lapse into a non-equilibrium state. Some of its components may come then into a relative, or quasi-equilibrium state
with external conditions, with the climate in this particular case. Complete equilibrium, however, cannot be achieved because of the instability of the climatic system itself. Such kind of models agree with reconstructions ofpaleolandscapes for epochs of global warmings when it took centuries for geosystems to accommodate.
As shown by our studies, both models - the equilibrium and non- equilibrium ones - exhibit cardinal differences for the same levels of warming. If we take the equilibrium model, transformations of the landscape attained to global dimensions in the past, up to the boundaries of natural zones being shifted for hundreds of kilometers. Say, if a temperature rise was just to 1 0 C, the subzone of coniferous and broad-leaved forests "moved" more than 400 km north; if the rise was 2 0 C, this subzone was 700 to 800 km north of its present position, while the tundra zone in Asia's northeast gave way to a forest-tundra. Such is the equilibrium model scenario.
As to the non-equilibrium model (when, as we have said, the new state of a global thermal regime takes a short time-dozens of years-to form), the above zones may stay put. Simulation studies, carried out at our Institute's laboratory involved with evolutionary geography, show this pattern: given analogous climatic changes, the coniferous and broad-leaved forests "move" no more than 8 to 10 km further north in 30 to 40 years.
But is it worth using equilibrium models at all? It is. First, because paleolandscape reconstructions on the basis of which such models are developed are a reliable source of data on the transformation of geosystems relative to a global warming at a given level; second, these models enable us to predict development trends for this or that component of a geosystems
and a finite equilibrium state this component tends to.
fe can outline a definite sequence of regional system- related prognostication to forecast anticipated changes of the climate. To begin with, we should study the present state of a concrete geosystem (first stage) and then (this is the second stage) examine in detail its present situation. Thereupon we can proceed to designing climatic change scenarios with the aid of paleorecon-structions and digital simulation data. That's the third stage. Next (fourth stage) we should identify expected characteristic time periods of response from individual landscape components to upcoming changes and single out those most sensitive to imminent changes within a definite stretch of time (by selecting the dominant processes and factors). And at the final, fifth stage we should make a close study of the role of the dominant factors and their cumulative effects. Synthesizing all the evidence thus obtained, we will
be able to come up with a prognosis of the geosystem's state before the anticipated change of the climate.
CLIMATIC SCENARIOS FOR NORTHERN EURASIA
Working at our laboratory, we have studied some characteristic changes of geosystems in this large geographical zone in anticipation of global warming. Studies conducted by my colleagues and me included such things as responses of the plant and soil cover, perpetually frozen ground and glaciation. There was some division of labor among our research teams. Thus, our Institute's Laboratory of Experimental Methods undertook hydrological computations; the Soil Science Department of the M.V. Lomonosov Moscow State University made a study of changes in the level of soil moisture; and the Institute of Agroclimatology at Roskomgidromet (State Committee on Hydrometeorology) assessed possible agroclimatic
changes. Let me stress that all these studies were based on an integral complex of reconstructions done at our laboratory.
And now over to the main characteristic features of landscape and climatic changes predicted for northern Eurasia's natural belts as a result of global warming.
In the European sector of the high-latitude insular Arctic, summer and winter temperatures are expected to go up in the first half of the 21st century by 3 to 4 0 C over the present level; in the Asian sector, the probable increase will be 2 to 3 0 C. The middle of the century may see a 4-6 0 C rise in the European Arctic, and its latter half may be in for a 6-8 0 increase in winter and 4-6 0 C in summer. Consequently, the Arctic Ocean will be ice-free for a longer period in the summertime, a factor that ship navigation could only benefit from. Yet on account of an enhanced inflow of humid air masses from the Atlantic, the annual amount of precipitation will be up-first by 100 mm, and then by 200 mm; this means that frequent rain- and snowfall and fog may pose difficulties for arctic shipping.
The areas of glaciers will shrink despite the appreciable rise in the amount of precipitation because both winter and summer temperatures will be climbing. By our preliminary estimates Novaya Zemlya and Novosibirskiye ostrova (isles) will be in for a bad snow accumulation deficit by the mid-century. Snow accumulation, necessary for the steady state of glaciers, will be down by half there; for Sevemaya Zemlya the fall will be even more dramatic, down to a fourth of the present level.
Here are some of the changes likely to be in store for the tundra belt to the south. Early in this century the East European and West-Siberian sectors of this territory will be in for a 3 to 4 0 C increase in summer and winter temperatures; the rise will be 1 to 3 0 C for the East Siberian part of the tundra belt. And the total increase in the amount of precipitation will be up to 100mm.
There are bound to be even starker contrasts by the mid-century. Although no significant changes will occur in wintertime temperatures within the East European sector of the tundra belt, its summers will become warmer by 4 to 6 0 C. There could be significant warming (by 8 to 12 0 C) in winter and in summer (by 6 to 8 0 C) east of the Polar Urals as far as the lower reaches of the Lena. Further east, January and July temperature rises will be smaller, from 4 to 6 0 C. As to the annual precipitation total, a maximum increase, 200 mm, will be between the Polar Urals and the Lena.
Yet despite the overall growth of precipitation, the moisture content of topsoil to a depth of 1 meter in the East European sector of the tundra belt is likely to contract by 0.5 cm early in the century (there will be no significant changes in the Asian sector, however). Still, some tentative appraisals of moistening factors allow us to say that the hydrothermal conditions in most of the regions of the East European Plain will remain level or even become a little more favorable, especially in the beginning of this century (today, by the way, the moisture content of ground and soil is excessive). It is possible therefore that the process of swamping in the tundra belt will be down, and some elevated tracts may even be in for aridization. In permafrost regions the ground layer of seasonal thawing will become deeper-from 20 cm in the first decades to 40- 60 cm in the mid-century Such thawing may cause intensive ground displacements on slopes, a factor that is going to have a negative impact on civil engineering projects, on gas-and-oil mining units and pipelines in particular.
In the latter half of the 21st century the ocean level will rise by 15 to 17 cm and even more, and cause a flooding of circumlittoral land. There are bound to be significant destructions of seashore in the eastern part of the Arctic Ocean whose shores are icebound for the most part.
What concerns the forest belt, we do not expect any substantial changes in the hydrothermal regime there early in this century. In its East European sector winter and summer temperatures will be about 3 0 C up, and by a mere 1-2 0 C off the southern boundary of the forestland. The sum total of annual precipitation will go up but a little. Yet the mean annual precipitation will be much down, to 55 mm, in the central part of the East European Plain on a large territory between Bryansk and Smolensk in the west and Vblogda and Nizhni Novgorod in the east. The moisture content in soil there will fall by 1.5 cm, or by 10 percent against the end of the 20th century.
The pace of bog formation is likely to decrease in the north of the forest belt. In southern regions there may be an increase in the biological activity of topsoil owing to its greater warming throughout the year, with not as stark temperature contrasts in between seasons.
The first decades of this century will witness the onset of significant changes within forestland plant communities, in particular, a "northward march" of deciduous trees, the birch in the first place. But the fir, which needs negative winter temperatures for normal growth, will be ousted from the western part of the East European forest belt in consequence of warming.
Geosystems of the belt's central districts are a special case: the amount of precipitation and the moisture content in topsoil are to mark a downtrend. These districts will be hit by more frequent droughts; so, overall, the soil-and-climatic potential of this territory will be deteriorating. Aridization will be conducive to a destruction of the mantle of soil because of intensive cracking and crumbling. Since the southern fringes of the forest belt (except valley forests) are mostly open plowland expanses, dust storms will be of frequent occurrence.
In the beginning of this century the river runoff will go down to 50 mm throughout the territory, and it will be down to 100 mm per year. In the Volga river basin it is estimated to fall by 15 percent over the present level. This, no doubt, will cause grave problems in terms of water supply, irrigation,
hydraulic resources for power stations, fishing and navigation. The condition of water pools will become worse.
In all likelihood, the aftereffects of the "hothouse effect" are to become more favorable by the mid-century throughout the East European forest belt. Winter temperatures will be up by 4- 6 0 C (by 10-12 0 C in the Volga-Vyatka Region), while summer temperatures, by a mere 1 -2 0 C. The annual precipitation total is to increase by about 100 mm (in central districts too); the moisture content in soil along the southern perimeter will stay close to the present level, and it will decrease somewhat up in the north. The agroclimatic potential of most regions of the East European sector will climb by more than 20 percent over the present level.
Early in this century the Siberian part of this forest belt will see about the same changes as the East European one. Along the middle reaches of the Ob and the Irtysh, too, there will be a region where the amount of annual precipitation will contract by more than 50 mm, and the soil moisture content will be down by 0.5 cm. Consequently, bog formation processes will be slowing down.
Our computations with the use of non-equilibrium models show that neither in the Siberian nor in the East European sector of the forest belt will the northern boundary of forests move to any significant extent into high latitudes, i.e. farther north. This might look like favorable climatic conditions brought about by the imminent warming. And yet even by the mid-century wood plants will hardly "advance" northwards by more than 8 to 10 km; only along river valleys they could be more aggressive in their northern thrust.
It is going to get warmer east of the Yenisei in the first half of the century: in central Yakutia, for instance, the mean January temperatures are to rise by 8 0 C, and in the north of the republic, by 8 to 10 0 C; so the topsoil layer ofsummertime thawing will get 40 to 60 cm deeper. The overmoistening of the ground may tell badly on arboriculture.
The situation will be different in the southern steppes of the East European Plain, which are an arid and semi-arid belt. Here winter temperatures will rise at first by 1 - 3 0 C and then by 2- 5 0 C towards the mid-century; but sum-mertime temperatures may even go down by 20 C by the middle of the century The annual precipitation total will be up 200 to 300 mm in the west and 100 mm to the east, in Kazakhstan. This will be a factor contributing to steady and high crops. Preliminary estimates for the European Plain's south indicate that already in the beginning of the century the agroindustrial potential of these regions will go up by 2 to 5 percent, and even by 25 percent in what is now the arid southeast.
But on the other hand, the higher level of precipitation will certainly stimulate soil erosion, it will be conducive to active erosion processes in ravines, to formation of rain rills and landslides. Therefore a system of preventive measures will be needed to combat such natural phenomena.
Particular attention should be given to such regions as Caucasia as well the mountains of Central and East Asia. The forthcoming warming will activate cyclones and atmospheric precipitation there. All this will combine into natural disasters like mud-and-rock torrents, landslips and avalanches. The situation will become especially dangerous in the Caucasus. The mountains of Central Asia, too, will be the scene of vigorous relief-formation processes and landslides. Besides, alluvial cones of mud and rock will pile up there. The mountain regions of Siberia will not be better off either: avalanches will combine with dangerous displacements of large blocks on mountain slopes. We need not tell you how tragic the consequences of these natural calamities could be.
The condition of glaciation in mountain districts is of particular importance, sure. By our tentative estimates, the balance of the mass of glaciers in the Caucasus will stay negative, but their degradation in the next few years will slow down. In Central Asia, however, the rising precipitation total will cause a growth of glaciers. The positive balance of their mass would add to the water content of the rivers they feed, among them of the Amu and Syr Darya. Should this scenario come true, it will have a positive effect on the water balance of the Aral Sea and surrounding territories.
WINNERS AND LOSERS
Man-induced changes of the climate can thus act upon geosystems. Overall, the consequences appear to be on the "plus" side. Indeed, this promises higher crops, an increase in the total volume of phytomass, and so forth. And yet we'd better not hurry with our conclusions. Man will have to adjust to climatic changes, though favorable for the most part (milder conditions up in the north, fewer sunny days in the south). So we should assess the situation in all its bearings. Man is still heavily dependent on his environment, even more so.
Therefore studying the state of geosystems in quasi-equilibrium is one of our priorities for the near future. Changing to a state of non- equilibrium, such systems are more sensitive to any outside interferences. We have no alternative to pooling the intellectual and material potential of society toward identifying all possible scenarios for each particular region. Considering the dynamics of geosystems what with the "hothouse effect", such scenarios should become part and parcel of long-term economic development programs and use of natural resources. Otherwise the imminent changes will catch us unawares.