* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Uncertainties of Climate Change in Arid Environments of Central Asia
Low-carbon economy wikipedia , lookup
2009 United Nations Climate Change Conference wikipedia , lookup
Michael E. Mann wikipedia , lookup
Mitigation of global warming in Australia wikipedia , lookup
Soon and Baliunas controversy wikipedia , lookup
Climatic Research Unit email controversy wikipedia , lookup
Heaven and Earth (book) wikipedia , lookup
ExxonMobil climate change controversy wikipedia , lookup
Climate resilience wikipedia , lookup
Global warming controversy wikipedia , lookup
Global warming hiatus wikipedia , lookup
Climate change denial wikipedia , lookup
Fred Singer wikipedia , lookup
Climate engineering wikipedia , lookup
Economics of global warming wikipedia , lookup
Climatic Research Unit documents wikipedia , lookup
Climate change adaptation wikipedia , lookup
Climate sensitivity wikipedia , lookup
Instrumental temperature record wikipedia , lookup
Climate governance wikipedia , lookup
Effects of global warming on human health wikipedia , lookup
Global warming wikipedia , lookup
Physical impacts of climate change wikipedia , lookup
Citizens' Climate Lobby wikipedia , lookup
Carbon Pollution Reduction Scheme wikipedia , lookup
General circulation model wikipedia , lookup
Climate change in Saskatchewan wikipedia , lookup
Politics of global warming wikipedia , lookup
Media coverage of global warming wikipedia , lookup
Climate change in Tuvalu wikipedia , lookup
Climate change and agriculture wikipedia , lookup
Effects of global warming wikipedia , lookup
Attribution of recent climate change wikipedia , lookup
Scientific opinion on climate change wikipedia , lookup
Solar radiation management wikipedia , lookup
Climate change in the United States wikipedia , lookup
Climate change feedback wikipedia , lookup
Public opinion on global warming wikipedia , lookup
Global Energy and Water Cycle Experiment wikipedia , lookup
Climate change and poverty wikipedia , lookup
Effects of global warming on humans wikipedia , lookup
Surveys of scientists' views on climate change wikipedia , lookup
Reviews in Fisheries Science, 14:29–49, 2006 Copyright © Taylor & Francis Inc. ISSN: 1064-1262 print DOI: 10.1080/10641260500340603 Uncertainties of Climate Change in Arid Environments of Central Asia ELENA LIOUBIMTSEVA AND ROY COLE Department of Geography and Planning, Grand Valley State University, Allendale, Michigan, USA This article examines the key uncertainties of climate change in the Central Asian republics of the former USSR—a vast arid region and a classic example of complex and poorly understood interactions between the regional responses to global climate change and the local human-induced desertification. Based on paleoanalogous scenarios, Central Asian deserts are often predicted to become wetter as a result of global warming because they are located north of 30◦ latitude. However, despite some similarities between the paleoclimate changes and greenhouse warming, such predictions have very serious limitations. Climate models predict that the temperature in arid Central Asia will increase by 1–2◦ C by 2030–2050, with the greatest increases in wintertime. Some models project greater aridity in the future though others project less aridity, and it is becoming increasingly apparent that climate change modeling in arid zones is extremely uncertain because of the extreme natural variability (both temporal and spatial) of the desert climate. The physical differences of climate change forcings imply that one might expect quite different regional responses to future human-induced climate change compared to the Holocene climate in terms of their rapidity and amplitude. Local and regional human impacts, such as massive irrigation, may have a stronger impact on the climatic system at the regional level than global climate change. Keywords paleoclimatology, greenhouse warming, climate models, paleogeographic data, human-induced desertification Introduction Sound use of aquatic and land resources in arid zones cannot be developed without a profound understanding of the processes of climate change. Much paleogeographic research in many arid regions of the world indicates that deserts and semi-deserts are prone to rapid geomorphological, hydrological, biological, and biogeochemical changes in response to global climatic change (Goudie, 1994; Varushchenko et al., 1987; Lioubimtseva et al., 1998) and have often been predicted to be among the most responsive ecosystems to higher carbon dioxide concentrations and global warming (Melillo et al., 1993; Bazzaz et al., 1996; Smith et al., 2000). Recent modeling studies (Wang and Eltahir, 2000; Zolotokrylin, 2002; Claussen et al., 2003) have shown the strong sensitivity of arid climates to changes in the surface parameters that can be triggered by human activities. Despite the growing understanding of the international scientific community of the regional impacts of global climate change, relatively little attention has been given to the climate and environmental Address correspondence to Elena Lioubimtseva, Grand Valley State University, Department of Geography and Planning, 1 Campus Drive, Allendale, MI 49401-9403, USA. E-mail: lioubime@ gvsu.edu 29 30 E. Lioubimtseva and R. Cole change of Central Asia. The recent reports of the Intergovernmental Panel on Climate Change (IPCC, 2001) and the international scientific literature in general, contain very little discussion of possible implications of global change for this enormous arid region. However, the question of trends and cycles of climate change in the arid lands of Central Asia have been attracting the attention of Russian geographers since the 19th century (Berg, 1904). Based on the evidence of paleoenvironmental changes and historical and archaeological data many Russian scientists attributed the decline of the classical and medieval civilization of Turkistan to an increase of aridity (Shnitnikov, 1969; Doluhanov, 1985; Varushchenko et al., 1987). Other researchers rejected the hypothesis of natural climate trends in this region suggesting instead that the climate and environmental changes of the last millennium were caused exclusively by human-induced processes (Markov, 1951; Kharin et al., 1998). Yet the question formulated by Markov more than half a century ago “is Central Asia getting drier?” still remains open. It is extremely difficult to draw a clear boundary between local and regional responses to global climate change and the trends caused by local land use changes, such as massive irrigation, overgrazing, and the consequent desertification processes. The Central Asian deserts are not pristine environments; grazers have exploited them for thousands of years, and in the 20th century, large irrigation schemes have been added to these landscapes. Although the drama of the Aral Sea crisis has been attracting the attention of the Russian and international scientific communities during the last decades, still remarkably little thought has been given to connections between the local and global changes in the region and the effects of massive irrigation on the climate of the Central Asian republics. To fully understand the impact of human activities, it is necessary to consider the extent to which anthropogenic effects have modified the background level of carbon storage, and whether change in the intensity of either process has any evident potential to take up or release carbon from the desert-zone carbon reservoir. Great uncertainties still exist about carbon pools in the desert soils. Figures on soil organic carbon given for this region in some widely used global datasets (Zinke et al., 1984) seem to be seriously overestimated (Adams and Lioubimtseva, 2002) and, although much of attention has been given to estimations of vegetation biomass and production in this region (Nechaeva, 1984; Bazilevich, 1995), the question of organic carbon in desert and semi-desert soils is poorly documented (Lal and Kimble, 2000). Confusion between organic and inorganic carbon in desert and semi-desert soils, or inadequate translation from Russian into English, are often the main reasons why Western authors tend to overestimate the levels of organic carbon in these soils. Realistic assessment of the region’s carbon budget is important for governmental decisions on land use and understanding of the implications for climate change (Lioubimtseva and Adams, 2002). The purpose of this article is to discuss the state of our current understanding of climate change in the republics of Central Asia and to outline the major uncertainties of climate and environmental change in this region. Particular attention is given to interactions between the effects of global change and the regional human-induced land degradation in the region. The following section provides a brief overview of the study region, its climate and physiography. Section three addresses the Holocene changes in Central Asia based on the regional biostratigraphic, geomorphological, and archeological data. Section four discusses current trends of climate change based on meteorological and remote sensing data series and also highlights some major sources of uncertainties and contradictions affecting climate change predictions and modeling in arid zones of Central Asia. Section five analyzes possible implications of climate change for desert and semi-desert landscapes and their carbon budget based on field and laboratory experimental data on direct physiological responses to CO2 in the study area and other arid regions of the world. It also discusses Climate Change in Central Asia 31 some contradictions between the existing biogeography model scenarios and the recent experimental data. Finally, section six addresses several major factors of human-induced degradation of arid landscapes. Brief Overview of the Study Region, Climate, and Physiography The five central Asian states of the Commonwealth of Independent States (CIS), formed in December 1991 after the break-up of the former USSR, Kazakhstan, Kyrgyzstan, Tadjikistan, Turkmenistan, and Uzbekistan, occupy an area of about 3.5 million km2 with a combined population of more than 57 million people (PRB, 2002). Deserts cover more than 95% of the total territory of Turkmenistan and more than a half of Uzbekistan and Kazakhstan. The Central Asian arid region comprises the entire Turan Lowland and the southern margin of the Kazakh Hills (Figure 1) and is bounded by the Middle Asian mountains (up to 7450 m) on its southern and southeastern edges. In the southwest, the somewhat lower mountains of the Kopet Dagh (2000 m) allow monsoon precipitation to reach the western slopes of the Tian Shan and Pamiro-Alaı̈ ranges. In the north, the Turanian plain descends Figure 1. The study region and its climate. 32 E. Lioubimtseva and R. Cole progressively northward and westward and opens out towards the Caspian lowland. The northern boundary of this vast arid zone is rather poorly defined but it lies at approximately 48◦ N. The deserts and semi-deserts of Central Asia have a typical continental climate and can be divided into two climate subregions—northern (mainly Kazakhstan) and southern or Irano-Turanian (Petrov, 1976; Lioubimtseva, 2002). In the north of the semi-desert zone, the winters are very cold with a mean winter minimum of −26◦ C and absolute minimum around −40◦ C or colder and the annual precipitation from 155 to 270 mm. Precipitation in the northern deserts is associated mainly with the prevailing westerlies and has a distinct maximum in spring-summer as the influence of the Siberian high diminishes and convective activity becomes stronger. In the southern Iranio-Turanian part of the region winters are milder with mean January temperature ranging between −10 and 0◦ C. The average July temperatures are about 32◦ C with a maximum of 52◦ C in the eastern Kara Kum. Precipitation in this subregion has a spring maximum that is associated with the northward migration of the Iranian branch of the Polar front. Most frequently, rain is brought by the depressions, which develop over the Eastern Mediterranean, migrate northeastwards, and regenerate over the Caspian Sea (Lioubimtseva, 2002). Westerly cyclones of the temperate zone change their trajectories in summer over the Aral Sea from a west-east to a northsouth direction and approach the zone affected by the Indian monsoon over the Zagros Mountains. Evidence of the Holocene Climate Change Numerous biostratigraphic, geomorphological, and archaeological proxy data indicate that the climate of the region has experienced many changes over time. Climatic variations through the late Pleistocene resulted in multiple shifts from hyper-arid deserts to subhumid shrub lands (Kes et al., 1993; Varushchenko et al., 1987; Velichko et al., 1987; Tarasov, 1992; Tarasov et al., 1998). However, in contrast with tropical deserts (i.e., the Sahara Desert), these environmental changes had relatively small amplitudes in the Late Pleistocene and Holocene, when the plains of Central Asia remained arid during long periods of time interrupted by relatively short humid intervals. Pollen evidence suggests that these fluctuations of precipitation did not exceed 150–200 mm. Among the relict features, the activity of ancient water flows during the periods of glacial melting in the mountains of Pamir, and Tien Shan left its distinctive traces both on the piedmonts, dissected by deep dry valleys, and on the aeolian plains, where alluvial fans formed, altering their location at each stage of alluvial deposition. Available biostratigraphic, geomorphologic, and archaeological data suggest that a severe arid phase of the Last Glacial Maximum (about 21,000 BP) was followed by the increase of humidity at the beginning of the Holocene. According to available pollen data in northern and central Kazakhstan, annual rainfall during the LGM was lower than now by 100–150 mm (Aubekerov et al., 1989; Tarasov, 1992). The dry cold steppes of the Younger Dryas were replaced in the Holocene by mesophytic forest-steppe vegetation with a maximum increase of arborescent species. The Holocene global optimum caused an increase of precipitation in many desert regions of the world. In the Kyzyl Kum desert, the Holocene climatic optimum is known as the Lavliakan humid phase and has been dated by radiocarbon from 8 to 4000 BP, with a maximum around 6000 BP (Doluhanov, 1985; Kes, 1993). Such climatic conditions favored the development of subhumid steppes (Artemisia and Graminea) on the currently desert Ustyurt plateau (Varushchenko et al., 1987; Tarasov, 1992). Climate Change in Central Asia 33 Marine fossils, relict shore terraces, archeological sites, and historical records point to repeated major recessions and advances of the Aral during the past 10,000 years. Until the present century, fluctuations in its surface level were at least 20 m and possibly more than 40 m. Significant cyclical variations of sea level during this period resulted from major changes in river discharge into it, caused by climatic alteration and natural diversions of the Amudarya away from the Aral sea (Micklin, 1988; Kes et al., 1993). Multiple smaller fluctuations of aridity in this region occurred also at a finer temporal scale. Historical documents and archaeological data in western Turkmenistan and Kazakhstan indicate that precipitation was slightly higher than today between the Caspian and Aral Sea between the 9th and 14th century AD, followed by the present day conditions (Varushchenko et al., 1987; Doluhanov, 1985). Explanation of the precipitation changes in the deserts of Central Asia center on the shifting westerly cyclonic circulation, dependent on the position of the Siberian high. The level of the Caspian and Aral Seas and their impact on local precipitation through the contribution of moisture and heat to the lower atmosphere are also very important in controlling precipitation. The impact of the Caspian Sea on precipitation is evidence of a very strong connection between the climate of Central Asia and the climate of European Russia because the level of water in the Caspian Sea depends entirely on run-off from the Volga and Ural basins. The level of the Aral Sea depends on the run-off from the Syrdarya and Amudarya rivers and ultimately on the rhythm of the glaciations in the Pamir and Tian Shan mountains. The Holocene optimum and earlier interglacials (for example, isotopic stage 5e, about 125,000 BP) are often suggested as possible analogous scenarios for a predicted global warming caused by increasing concentrations of greenhouse gases in the atmosphere. Although palaeodata indeed provide valuable insights on possible geomorphological, hydrological, and biological responses to climate change, caution should be exercised in predicting future trends with palaeoanalogues. Strong agreement exists between climatologists that the climate transition from the LGM conditions to the Holocene was triggered by changes in seasonal sunlight distribution caused by oscillations in the Earth’s orbit and axial tilt (Berger, 1978). The physical differences of climate change forcing imply that one might expect quite different regional responses to future human-induced climate change compared to the Holocene climate in terms of their rapidity and amplitude. Current Trends and Model Scenarios Based on palaeoanalogous scenarios, Central Asian deserts are often predicted to become moister as a result of global warming because they are located north of 30◦ latitude and are expected to benefit from the southward shift and probable intensification of the westerly cyclones similar to the early Holocene conditions. While palaeodata may improve our understanding of the global and regional mechanisms of climate change during relatively long time intervals (centuries and millennia), they usually do not capture the pattern of finer fluctuations of temperature and precipitation. The Intergovernmental Panel on Climate Change (IPCC) report Regional Impacts of Climate Change, 2001 provides very limited information about climate change in arid Central Asia (IPCC, 2001). “There were no discernible trends in annual precipitation during 1900–1995 for the region as a whole, nor in most parts of this region” (IPCC, 2001, Chapter 7). The report does point out a likely 1–2◦ C/century temperature increase for Central Asia. The aridity index shows no consistent trends for Central Asia as a whole (IPCC, 2001). A most commonly used measure of aridity is Thornthwaite’s index of aridity (Thornthwaite, 1948) defined as a ratio of precipitation and evapotranspiration (P:PET). Most of Central 34 E. Lioubimtseva and R. Cole Figure 2. Temperature increase from 1900 to 2000. (a) Toshkent station (adapted from Chub, 2000). (b) temperature anomaly for 1880 to 2000 for arid zones of Central Asia (based on GHCN dataset, Peterson and Vose (1997)). Asia lies in the zone in which the aridity index varies between 0.05 and 0.5 and consequently is defined as “arid” and “semi-arid” by the United Nations Environmental Program (UNEP) classification (1992). It is clear that one of the most important consequences of the temperature increase in arid lands is the increase of evapotranspiration, and therefore aridity. Meteorological data series show a steady increase of annual and winter temperatures in this region since the beginning of the past century (Figures 2a and 2b). However, few stations have data for longer than a century; most have observations for just half that time. In addition, many stations have stopped functioning since the collapse of the USSR: the number of snowgauging stations in the river basins of Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan, for example, has decreased from 257 in 1985 to 30 in 1995 (Borovikova, 1997). Available historical precipitation data from the Hulme (1998) global dataset do not show any significant changes in precipitation in Central Asia since 1900 (Figure 3). This Figure 3. Precipitation in Central Asia, 1900–2000 (based on the CRU dataset, Hulme (1998)). Climate Change in Central Asia 35 database, most commonly used in the modeling studies, is based on a very small number of stations located in the region, and is prone to errors caused by the extrapolation of data from only few stations over a very large area. Furthermore, there is uncertainty regarding these data because most of the sites are located near irrigated areas. Despite the absence of an overall precipitation change noticeable for the entire region, great spatial variability has been observed at the landscape scale. For example, a study by Neronov (1997) in eastern Turkmenistan revealed significant differences between the trends of annual precipitation and aridity index in the sandy desert of the eastern Kara Kum and the neighboring irrigated lands. He analyzed annual and monthly temperature and precipitation data from the Repetek meteorological station (located in the quasi-pristine landscape of sandy desert within the Repetek biosphere reserve) and Bayramaly stations (located in the Murghab oasis with extensive irrigated lands, 110 km southeast from Repetek), covering the periods of 1919–1997 and 1890–1997, respectively. Both sites have experienced very similar temperature increases during the period of instrumental observations and especially since the middle of the past century. Steady temperature increases in these two stations and in the Turanian deserts in general (Figures 4a and 4b) might be an indication of some general factor affecting atmospheric circulation in Central Asia. For example, the steady increase in both mean annual and mean winter and summer temperature trends could be the result of the decreasing effect of the southwestern periphery of the Siberian high in winter and the intensification of summer thermal depressions over Central Asia. Precipitation trends show a dramatic difference between the two sites as well, and are apparently responsible for the difference between the trends of the mean annual aridity index. Although the index of aridity increased almost twice (from 0.42 in 1891 to 0.71 in 1994) in Bayramaly, there was only a slight change from 1910 to 1954 (0.41 to 0.46). A steady increase of precipitation, especially since the middle of the 20th century was also reported for several oases in Central Asia (e.g., Kirsta and Rihlov, 1988) and can be attributed to the micro-regional, humaninduced climate change caused by the expansion of irrigated lands. Such trends usually show remarkable spatial variability and are much more intensive in the big oases where the area of irrigated lands has dramatically grown during the past century (such as Urganch, Bokhora, and Toshkent oasis in western Uzbekistan or Murgab, Tedjen, and Ashgabat oases in Turkmenistan). Another area where the regional weather records show a significant climate change since the 1960s is in the vicinity of the Aral Sea, where a general trend towards a more continental climate has been suggested by data from stations located near the shore. Such data indicate an increase in summer and decrease in winter air temperatures of 1.5–2.5◦ C, a decline in the mean annual relative humidity of 2–3%, and an increase in the occurrence of drought days by 300% (Middleton, 2002). Precipitation records also show a shift in seasonality. While in the 1950s the maximum precipitation in the Aral Sea area occurred during February–March and the minimum in September, in the 1970s the maximum was observed in April and the minimum in July. Spring frosts have been recorded later and autumn ones earlier (Glazovsky, 1995; Middleton, 2002). The reduction of the sea surface area also caused a significant decrease of precipitation since the 1960s and saline dust from the exposed lakebed has been implicated in rapid climate and vegetation change. Paradoxically, despite the increasing water shortage in the Amudarya delta, there has been a rather stable trend of increasing precipitation during the last decade indicated by data from several stations situated in irrigated areas of the Amudarya delta, such as Nukus, Takiatish, Chimbay, and Kungrad (Victor Statov, personal communication, 2003). It is important to note, however, that there is still significant uncertainty in the estimations of the extent of arid lands in the temperate zone of Eurasia as a result of ambiguity 36 E. Lioubimtseva and R. Cole Figure 4. Precipitation, temperature, and aridity index (P/PET). (a) Repetek Station, Turkmenistan, 1910 to 1995. (b) Bayramaly Station, Turkmenistan, 1910 to 1995. Adapted from Neronov (1997). in the indices of aridity used in different studies. The boundary between arid and semi-arid climates as shown on the commonly used UNEP map (1992), which was based on the Thornthwaite index, is located 150–200 km south of the arid/semi-arid boundary of the USSR climate classification. Long temporal series of remotely sensed data offer another useful approach to climate change-monitoring based on the estimation of the statistical relationship between climate aridity and vegetation phytomass estimations from satellite imagery (Kogan, 1995; Lambin, 1997; Nicholson et al., 1998). Most of this research focused on climate change in the Sudan-Sahelian zone of Africa and the western U.S. Zolotokrylin (2002) developed a new empirical aridity index for Central Asian deserts and semi-deserts, Climate Change in Central Asia 37 which can be defined as a duration of the period with a normalized difference vegetation index (NDVI) less than 0.07. The NDVI is defined as the normalized difference of reflectance in red and infrared bands of the electromagnetic spectrum. This indicator reflects the zonality of heat exchange between arid land and atmosphere as the relation of radiation and evapotranspiration mechanisms in the regulation of thermal conditions of soil surface and the lower layer of atmosphere (Zolotokrylin, 2002). Analyses of the National Atmospheric and Oceanic Administration AVHRR temporal series since the 1980s showed a decrease in aridity from 1991–2000 compared to 1982–1990 in the northern part of the region (mainly Kazakhstan) and a southward shift of the northern boundary of the desert zone in Central Asia (Zolotokrylin, 2003). Kharin et al. (1998), using the NOAA advanced very high resolution radiometer (AVHRR) series for the assessment of precipitation and land degradation since 1982, also points to a possible decrease of aridity in this region during the past decades. Their studies in Uzbekistan and Turkmenistan indicate an increase in vegetation phytomass associated with local precipitation increase from 10 to 30% from 1982 to 1992. Nonclimatic factors, such as land-use changes, may affect the growth and vigor of green vegetation, and NDVI changes may not always be perfectly correlated with precipitation change. Although remote sensing data provide useful insights into the relationship between the NDVI and precipitation, the duration of such observations is still too short to describe climate change variations and trends realistically. Data have been collected in several parts of Central Asia that seem to indicate that precipitation has increased at the end of the 20th century. However, because this trend has been identified only for a very short period of time it is difficult to say it is evidence of a manifestation of some cyclic pattern of precipitation at a decadal scale or a part of some longer-term trend responding to either regional or global factors. The very existence of arid ecosystems is related to their temporal climatic variability, and together with vegetation, cover characteristics that represent the major challenge for climate monitoring and modeling. Climate models predict that the temperature in arid Central Asia will increase by 1– 2◦ C by 2030–2050, with the greatest increase in winter. Precipitation projections vary from one model to another and projected changes in the aridity index for different model runs show no consistent trend for this regions (Figures 5a and 5b). Some models project greater aridity in the future and some lower, and it is becoming increasingly apparent that climatechange modeling in arid zones is extremely uncertain, partly because of the extreme natural variability (both temporal and spatial) of the desert climate and partly because of inherent uncertainties in global and regional climate modeling. Atmospheric dynamics are known to be very sensitive to natural climate variability at relatively short time-scales and the effect of short-time variability on longer (decadal-to-millennial) time-scales are not fully understood. The existence of the Turanian deserts of Central Asia results from their inland location, orographic effects on the flow of air masses, and is largely governed by topography. The mechanisms of mid-latitude aridity, however, are not limited to “rain shadow effects” of the mountains but are largely the effects of mountains on the polar jet stream. The interaction of mountain ranges with the polar jet determines regions of frequent passage of intertropical disturbances. The spatial scale of existing models and downscaling techniques are still insufficient in understanding climatic data in their regional and local context, especially in the zones with complex topography. Both theoretical considerations and numerical models have shown a significant sensitivity of the climate of arid regions to vegetation distribution. Ground-cover parameters can significantly alter the modeled climate (Claussen et al., 2003; Wang and Eltahir, 2000). Climate change scenarios, unfortunately, do not incorporate regional controls on climate. The 38 E. Lioubimtseva and R. Cole Figure 5. GCM scenarios for arid zones of Central Asia, 2020 to 2080 (derived from IPCC-DCC data). (a) Temperature range (degrees C). (b) Precipitation range (mm per day). Climate Change in Central Asia 39 impacts of the extensive redirection of montane and lacustrine water resources to irrigated agriculture in Central Asia and the degradation of the Aral Sea remain unmeasured in current climate models, yet may be of significant importance in regional climate change. Although it is clear that both observed and predicted climate changes might be partly caused by global climate change and partly by local anthropogenic processes, it is extremely difficult, if not impossible, to delineate the boundary between these two factors. Possible Implications of “Greenhouse” Warming for Central Asian Deserts While the predictions based on the paleoanalogues, recent climate trends, and General Circulation Models (GCM) scenarios still rather strongly disagree about the direction, frequency, rapidity, and amplitude of the possible regional climate changes that might be caused by the global greenhouse warming, it is likely that any changes in the regional circulation and climate regime will affect various landscape components, such as vegetation, soils, hydrological regimes, biogeochemical cycles, and landforms. It is not our goal here to evaluate the probability of one or another regional climate change scenarios but rather to discuss possible implications of the probable climate changes for the arid environments of Central Asia. Possible Hydrological and Geomorphological Responses Arid environments are prone to rapid and often unpredictable hydrological and geomorphological changes in response to apparently modest climatic stimuli, switching from one state to another when a particular threshold is reached (Goudie, 1994). Such responses may include changes in surface and underground runoff, sediment transport, groundwater and lake levels, erosion and deposition rates, and many other related processes. In order to discern the effect of climate change on hydrological processes, changes in precipitation, evapotranspiration, infiltration, groundwater storage, and various components of total runoff must be considered. This is possible only through the implementation of a continuous hydrological simulation models that couple land-atmosphere interactions and subsurface hydrological surfaces together (Loaiciga, 2003). Runoff scenarios for arid regions are still very imprecise, but the evidence suggests that even insignificant changes in precipitation and evapotranspiration are likely to result in proportionally larger changes in runoff. Shiklomanov (1999) showed that an increase in mean annual air temperature by 1–2◦ C and a 10% decrease in precipitation could reduce annual river runoff by up to 40–70% for river basins in areas of water deficit. Up to the present time, most assessments of changes in the hydrological regime of Central Asia have been based on GCM scenarios coupled with hydrological models and have involved tremendous simplification caused by the coarse resolution of the numerical grids. Nested hydrological models within regional climate models (RCMs) linked with GCM could provide much more detailed analysis but such simulations are still very expensive. Global warming could have a dramatic effect on the Caspian Sea, where a 2–3◦ C increase in air temperature would lead to increased precipitation and greater discharge from the rivers such as the Volga and Ural and a further increase of the sea level (Shiklomanov, 1999). Climate change might also affect snow and ice storage and melting starting in the Pamir and Tian Shan Mountains and hydrological regimes of two major Central Asian rivers—the Syrdarya and Amudarya that drain into the Aral Sea. It is, however, very unlikely that increased river runoff would be able to balance the shrinking of the Aral Sea caused by irrigation. Another probable effect of climate change in this region has to do with recent changes in wind erosion and dust storm activity. Changing dust storm frequencies in this region during the past century have been largely attributed to human-induced desertification (Middleton, 40 E. Lioubimtseva and R. Cole 2002; Glazovsky, 1995). It is still unclear how such processes might be modified in the future, given their recursive nature and the complexity of their relations with climatic, vegetation, soil, and land-use variables. Possible Implications of CO2 Increase for Desert Vegetation and Soils One of the most intriguing questions about possible implications of global climate change for desert ecosystems is how arid vegetation and other photosynthesizing organisms would adapt to the increasing concentrations of CO2 and how this would affect other processes in arid ecosystems (e.g., hydrological cycle, biogeochemical cycles, etc.). In addition to its effect on climate, an increased atmospheric CO2 concentration has direct and relatively immediate effects on two important physiological processes in plants: it increases the photosynthetic rate, but decreases stomatal opening and, therefore, the rate at which plants lose water. The combination of these two factors—increased photosynthesis and decreased water loss—implies a significant increase of water efficiency (the ratio of carbon gain per unit water loss) and productivity and a reduction in the sensitivity to drought stress in desert vegetation as a result of elevated atmospheric CO2 (Smith et al., 2000). No regional modeling studies have been conducted in this region but global biogeography models (Melillo et al., 1993; Woodward et al., 1998) predict relatively strong responses of arid ecosystems to global climatic change. The Kara Kum and Kyzyl Kum Deserts of Central Asia are strongly dominated by vegetation with C3 photosynthetic pathway with only few C4 and Crassulacae Acid Metabolism species (mainly succulents). It is often expected that plants using the C3 photosynthetic pathway will respond more strongly to raised CO2 than species with the more water-efficient and CO2 -efficient C4 photosynthetic system (Table 1). The significance of different photosynthetic pathways in the adaptation of perennial plants to life in extreme desert environments is still hotly debated (Whitford, 2002). Most publications on this subject are based on chamber experiments and the recent free-air CO2 -Enrichment experiments studying responses of desert vegetation to increased CO2 levels conducted in the southwestern U.S. where desert vegetation cover is dominated by C4 species. Much research on vegetation responses to elevated CO2 concentrations was conducted in the former Soviet Union in the 1970s and 1980s. CO2 -enrichment experiments (both chamber and free-air) conducted in the Kara Kum (Voznesensky, 1977) and Kyzyl Kum (Voznesensky, 1977; Zelensky, 1977) Deserts showed a 2 to 4 times increase in the photosynthetic rate under the saturating CO2 concentrations during several years. Three Kara Kum species (Eminium lehmanii, Rhemum turkestanuikum, and Ephedra stobilacea) responded with a six-fold increase in photosynthetic rate (Nechaeva, 1984). This probably can be explained by their very ancient origin dating back to past intervals with higher CO2 concentrations. Although theoretically, C4 plants have photosynthetic rates more than double those of C3 plants, among the Kara Kum species both C3 species (Ferula litwinowiana and Smirnowia turestana) and C4 plants (Stpagroistis karlinii) showed significant responses to CO2 fertilization. It is important, however, to realize that these results are primarily based on chamber experiments and should be treated with caution. The results of CO2 fertilization experiments in other arid regions of the world, such as the Negev Desert in Israel (Grüenzweig and Köerner, 2000) and the Mojave Desert in the U.S. (Smith et al., 2000) are rather mixed—which only contributes to the uncertainty about the implications of the doubled CO2 concentrations for desert ecosystems. The CO2 fertilization affects not only higher vegetation but also microphytic communities including mosses, lichens, fungi, algae, and cyanobacteria (blue-green algae). 41 Smirnowia turkestana Sunecio subdentatus Rheum turkestanicum Tamarix ramosissim Populus pruinosa Ephedra strobilacea Atriplex dimorphostegia Stipagrostis karelinii Haloxilon persicum Salsola richteri Calligonum caput-medusae Species Compiled from Whitford (2002) and Nechaeva (1984). CAM C4 C3 Photosynthetic pathway Fixes C at night Higher than sunlight 1/4 full sunlight Light saturation Water loss rate (g H2 O/gC fixed) ∼600 ∼250 ∼50 Optimum temperature ∼25◦ C ∼45◦ C ∼35◦ C Table 1 Comparison of the general characteristics of C3, C4, and CAM 3–4 55–65 20–30 Photosynthetic rate (mgCO2 / dm2leaf h) 42 E. Lioubimtseva and R. Cole These microphytic communities form biogenic crusts on the soil surface varying from a few millimeters to several centimeters in thickness and play a significant role in the desert ecosystems controlling such processes as water retention and carbon and nitrogen fixation in soils. In the Kara Kum Desert of Turkmenistan, the accelerated growth of such biogenic crusts, known among the local herders as “karaharsang” (turk.-black moss), has been observed during the past 40–50 years and usually has been attributed to the undergrazing caused by the decrease of the wild fauna and insufficient pressure on the desert rangelands. It is possible, however, that the main reason for the accelerated growth of “black mosses” in the Kara Kum is a response of microphyts to increasing concentrations of CO2 in the atmosphere. If the increased CO2 concentrations result in the significant increase of vegetation productivity, one might also expect significant changes in runoff, precipitation regime, and circulation. It was demonstrated in several modeling studies in other arid regions (Wang and Eltahir, 2000; Claussen et al., 2003) that vegetation plays a prominent role in the energy, moisture, and carbon-exchange between the land surface in arid and semi-arid zones and the atmosphere. However, vegetation-climate feedbacks and their role in global and regional climate change are still relatively poorly understood and it is difficult to predict feedbacks caused by these possible changes in the desert vegetation cover. If indeed, the desert vegetation can respond to CO2 fertilization, it is still unclear how it would affect the surface runoff. So far these relations are not taken into account by climate models. Uncertainty about the changes in water-use efficiency and photosynthetic activity of desert vegetation due to increased CO2 in the atmosphere raises a very important question: have the vegetation changes in Central Asia, which were recently reported by several authors (Zolotokrylin, 2002; Kharin et al., 1998; Lioubimtseva, 2004) on the basis of field- and remote-sensing observations, been the result of precipitation changes (as these authors assume) or by physiological changes in arid plants? Uncertainties About Ecosystem Carbon Budget There is much uncertainty about the possible positive or negative impacts of global climate change on carbon sequestration in the vegetation and soils of the arid zones of Central Asia. The seasonal dynamics of CO2 fluxes on deserts and semi-desert vegetation of the region have not been measured until very recently and no data exist on their possible and longterm changes. Based on research on organic matter reserves and net primary productivity, Central Asian arid lands have the potential to sequester considerable amounts of carbon, if pasture productivity could be improved through more effective management techniques (Lioubimtseva and Adams, 2002; Guilmanov, 2002). Even more uncertain is the soil carbon budget of the region. It seems that commonly used global databases (e.g., Zinke et al., 1984) have tended to overestimate the carbon content in the deserts of the former USSR and Mongolia (i.e., 10.0 tC/ha in Zinke et al., 1984). Russian sources indicate much lower values for the same areas (between 1 and 3.5 tC/ha in dark sierozems and sandy soils and relatively high only in the light sierozems—up to 4.5 tC/ha in the first top 50 cm of soils) (Gladishev and Rodin, 1977; Lioubimtseva and Adams, 2002). The soil carbon values that were obtained for the Central Asian deserts seem to be overestimated due to the miss-assignment of sampling sites (Adams and Lioubimtseva, 2002). Preliminary estimations by Lioubimtseva and Adams (2002) suggest that the arid environments of Central Asia currently store between 7.0 and 9.0 Gt of organic carbon in the top 50 cm of soils. This is 3 or 4 times less than during the Liavliakan Pluvial (Holocene Climate Change in Central Asia 43 climatic optimum), when a warmer global climate and lack of human impact favored richer vegetation in this area (Lioubimtseva et al., 1998). However, these estimations are very rough and further research is needed to assess the carbon budget of this region. Human Impact and Land Degradation The practice of farming is ancient in Central Asia. Numerous artifacts of Mesolithic and Neolithic settlements are found all over this vast region and primitive forms of artificial irrigation existed in Turkmenistan and Uzbekistan more than 2000 years ago. The second major form of land use of this arid area that goes back many thousands of years ago is pastoral nomadism—an extensive, mobile form of land use that can have negative local environmental impacts in its traditional forms. Other human impacts include technological developments such as the excessive use of woody vegetation for domestic use and road building and drilling for water and oil. For this reason, any attempt to trace a clear boundary between the desert responses to global warming and the effects of local human activities would be extremely difficult. It is very likely that the effects of global change would be rather insignificant compared to the local human-induced processes, such as irrigation, overgrazing, ground water depletion, and many others effects of land use. Arid areas all over the world have shown themselves to be highly susceptible to the effects of human intervention (Goudie, 1994; Dregne and Chou, 1992; Glantz, 1999). Grazing Impact on Vegetation and Soils Grazing can exert both positive and negative effects on total vegetation cover, and by implication on soil organic carbon (which is derived from plant material). Moderate and rationally managed grazing generally favors sequestration of organic carbon in soils both directly (organic matter from excrement) and indirectly (preserving perennial grasses such as Carex physodes with well-developed root systems and high underground biomass). An overgrazed soil is easily eroded and blown away by the wind to form crescent dune (barchan) fields. In arid and semi-arid rangelands, overgrazing is the main reason for losses of both vegetation and soil carbon and nitrogen. The impact of grazing on vegetation, however, has been decreasing in the region during the past decades and is currently insignificant with the exception of Priaralye (the Aral Sea area) (Neronov, 1997; Kharin et al., 1998). In many parts of the Kara Kum and Kyzyl Kum Deserts, undergrazing rather than overgrazing has been the main reason for environmental changes. Cattle, camel, horse, and sheep populations have decreased dramatically in the Central Asian countries by 27%, 18%, 28%, 53%, respectively, over the last 10 years (FAO, 2003). Goats, which accounted for only 5% of the small stock (sheep and goats) in 1992, increased by 31% to account for 14% of the total small stock population in 2002. But overall, the numbers of small stock have decreased over the past 10 years by over 30 million head. With undergrazing, the loosening of the soil is too little and annual grasses or moss gradually replace the sparser natural perennial vegetation, and the surface becomes more compacted. Unprecedented growth of karaharsangs (microphytic communities) during the last decades in response to increasing CO2 fertilization usually occurs only in the undergrazed areas. Similarly, the pressing of seeds underfoot to the optimal depth occurs only with moderate numbers of animals per hectare of pasture. Perturbation of Climate by Irrigation Although artificial irrigation in oases of Central Asia has been known for almost three millennia, the most important environmental changes in this region have occurred during 44 E. Lioubimtseva and R. Cole the past 30–40 years as a result of massive irrigation schemes started in the 1960s (Glazovsky, 1995; Glantz, 1999). Irrigated arable land, principally for cotton monoculture, has increased by 60% in the region from 1962 to 2002 (FAO, 2003). The total irrigated area in the study area increased by over half a million hectares (5.2%) just from 1992 to 2002 (FAO, 2003). Turkmenistan alone accounted for 59% of the change, increasing its irrigated area by 300,00 hectares (20%). Total water withdrawals (all uses) were 125% of the average annual water resources in 1988 (Glazovsky, 1995). Such dramatic human-induced changes in the hydrological cycle led not only to a significant decrease of river runoff, changes in the number and area of lakes and rise of groundwater levels, but also to significant changes in evapotranspiration and precipitation. Both theoretical considerations and modeling experiments (Wang and Eltahir, 2000; Zolotokrylin, 2002) show that changes in albedo and other biophysical parameters of vegetation cover caused by massive irrigation might establish totally new equilibria in the climate-vegetation relations and reverse previously existing feedback mechanisms. While a desert environment is featured by strong negative biosphere-atmosphere feedbacks, perturbation of a large area by irrigation induces a positive feedback that brings the system to more humid climatic conditions with a new climate-vegetation equilibrium. Climate Change Caused by the Aral Sea Crisis Most research on climate change in the Central Asian republics during the past decades has been focused on the Aral Sea areas and an enormous number of publications exist on this subject, essentially in Russian (e.g., Molosnova et al., 1987; Semenov, 1990; Glazovsky, 1995; Zolotokrylin and Hmelevskaya, 1999; Chub, 2000). The Aral Sea desiccation caused prominent climate change not only in the coastal area but affected the entire atmospheric circulation system in its basin. Summer and winter air temperatures at the stations near the seashore increased by 1.5–2.5◦ C and diurnal temperatures increased by 0.5–3.3◦ C (Glazovsky, 1995; Chub, 2000). Near the coast, the mean annual relative humidity decreased by 23% and recurrence of drought days increased by 300% (Glazovsky, 1995). The annual cycle of temperature and precipitation has also changed. A seven-fold rise in the albedo of the area previously occupied by the Aral Sea caused a three-fold increase in reflected solar radiation and overall continentality of the climate (Chichasov, 1990; Glazovsky, 1995). In addition, the exposure of the former lakebed areas, especially on the eastern side of the Aral Sea, represents an enormous source of highly saline wind-blown material (up to 1.5% of salt in the total mass of hard particles transported by the wind). Deposition of the Aral Sea dust has been reported at a distance of several thousand miles from the source, and many data suggest that the aeolian deposition of salts has adversely affected the vegetation of vast adjacent areas. According to Semenov (1990) the amount of aeolian redeposition from the former Aral seabed is exceeding 7.3∗ 106 tons per year, comprised of between 5 and 7∗ 104 tons of salt per year, equivalent to 3000 commercial trains of 40 cars each. Today the drying bottom of the Aral Sea has became one of the biggest sources of dust aerosols in the world and must be considered in model simulations of both global and regional climates. Dust tends to cool the earth by reflecting sunlight back into space, and it decreases rainfall by suppressing atmospheric convection. GCM simulations of future climate, which include changes in dust loading, tend to yield different results from those that do not, and the incorporation of iterative feedbacks between simulated future climate, vegetation cover, and dust flux from changes in vegetation cover, tends to further amplify the changes in arid-land climates. Following an initial increase in rainfall over arid areas, Climate Change in Central Asia 45 dust flux decreases due to increased stabilizing vegetation cover and moister soils. This decrease in dust flux tends to cause rainfall to increase further. Although the world is generally forecast to become moister as greenhouse gas levels increase, this effect is patchy and according to certain models some desert areas may become drier. In this case increased dust flux may increase aridity and also suppress rainfall outside the desert areas themselves. However, at present the incorporation of dust feedbacks in models is in its early stages (Lioubimtseva and Adams, 2004). Conclusion Arid environments are projected to undergo significant changes under greenhouse warming, but there is considerable variability and uncertainty between different climatic scenarios. The complexities of precipitation changes, vegetation-climate feedbacks, and direct physiological effects of CO2 on vegetation present particular challenges for climate-change modeling of arid regions. Great uncertainties exist in prediction of arid ecosystem responses to elevated CO2 , as well as to the regional precipitation and evaporation changes caused by global climate change. There has been a general warming trend in arid Central Asia on the order of 1–2◦ C since the beginning of the 20th century with some fluctuations along the way. Such fluctuations of the past century seem to be comparable in their amplitude and frequency with the earlier climate variability during the second half of the Holocene. These short-term trends also show significant spatial variability caused by regional topography and other factors. Palaeodata provide important information about spatial patterns of change in arid environments in the past that can significantly improve our knowledge about the global and regional controls on climate change in arid regions. However, because the mechanisms of palaeoclimatic variability were different from those caused by the current greenhouse warming, any paleoanalogies should be treated with great caution. Precipitation projections in this region vary from one model to another but are unlikely to be significant. Despite the great progress in global climate modeling, the GCMs give very variable results, with large spatial differences in the areas forecast to receive higher or lower precipitation. The lack of integration of such factors as dust aerosols, biophysical and biochemical feedbacks caused by land-cover changes, as well as the regional factors of human-induced climate change such as irrigation, are the major sources of uncertainties. For example, the dust aerosols from the drying Aral Sea bottom may have a very significant impact on regional climate but are not taken into account by the models. Projections based on biogeographic models suggest considerable changes in desert and semi-desert vegetation due to a combination of greenhouse-related climate change and direct physiological CO2 effects on vegetation, such as changes in photosynthesis and water-use efficiency over the coming century. This could have implications for crop growth in desert-marginal areas, favoring greater productivity, and perhaps increase productivity and biomass of natural desert vegetation and soil organic matter. However, the very limited number of CO2 enrichment experiments in the Kara Kum and Kyzyl Kum does not always confirm this thesis. The accelerated growth of biogenic crusts (observed during the past 40– 50 years) in this arid region might be a response of microphyts to increasing concentrations of CO2 in the atmosphere. However, because such responses occur only on the undergrazed desert rangelands, it is still unclear if the CO2 increase is really the major cause or such growth or rather the land-use change. Local and regional human impact in arid zones can significantly modify surface albedo, as well as water exchange and nutrient cycles that might have potential impact on the climatic system both at the regional and global scales. 46 E. Lioubimtseva and R. Cole On the other hand, improved management techniques can increase the carbon sequestration capacity of semi-desert rangelands and arable lands. Acknowledgments The GCM scenarios were obtained from the IPCC Data Distribution Centre (http://ipccddc.cru.uea.ac.uk). Historical monthly precipitation data were obtained from Tyndall Centre for Climate Change Research, University of East Anglia. We are grateful to Philip Micklin and two anonymous reviewers for helpful comments, and Kin Ma who helped with editing the final version of this manuscript. References Adams, J. M., and E. Lioubimtseva. Some key uncertainties in the global distribution of soil and peat carbon, pp. 459–469. In: Agricultural Practices and Policies for Carbon Sequestration in Soil (Kimble, J. M., R. Lal, and R. F. Follett, Eds.). Boca Raton, FL: Lewis Publishers (2002). Aubekerov, B. Z., E. V. Chalihjan, and S. A. Zakupova. Izmenenija klimata i paleogeograficheshih uslovij Centralnogo Kazakhstana v pozdnelednikovie i golocene (Variations of climate and palaeogeographical conditions in Central Kazakhstan during the Late Glaciation and Holocene) pp. 98–102. In: Paleoclimati Pozdnelednikovia i Golocena (in Russian). Moscow: Nauka Publishers (1989). Bazilevich, N. I. Biomass and Biologic Production of Vegetation Formations of the Former USSR (Biomassa i bioproductivnost rastitelnih formatsij (in Russian)). Moscow: Nauka Publishers (1995). Bazzaz, F. A., S. L. Bassow, G. M. Berntson, and S. C. Thomas. Elevated CO2 and terrestrial vegetation: Implications for and beyond the global carbon budget, pp. 43–76. In: Global Change and Terrestrial Ecosystems (Walker, B., and W. Steffen, Eds.). Cambridge: Cambridge University Press (1996). Berg, L. S. Visihaet li Crednaja Azia? (Is Central Asia drying out?) Bulletin of the Imperial Russian Geographic Society, 40: 507–521 (1904). Berger, A. L. Long-term variations of caloric solar radiation resulting from the Earth’s orbital elements. Quaternary Res., 9: 139–167 (1978). Borovikova, L. N. Description of the state of the national hydrometeorological surveys and concept for their future development, Report No. 4, World Bank program 2.1, Improvement of Hydrometeorological Surveys in central Asia, Tashkent (1997). Chichasov, G. (Ed.). Hydrometeorological Problems of the Aral Sea Area (Gidrometeorologicheskije Problemi Priaralya) (in Russian). Leningrad: Gidrometeoizdat (1990). Chub, V. E. Climate Change and Its Impact on the Natural Resources Potential of the Republic of Uzbekistan (Izmenenija klimata I ego vlijanije na prirodno-resursnij potensial respubliki Uzbekistan) (in Russian), Gimet, Tashkent (2000). Claussen, M, V. Brovkin, A. Ganopolski, C. Kubatzki, and V. Petoukhov. Climate change in northern Africa: The past is not the future. Climatic Change, 57: 99–118 (2003). Doluhanov, P. M. Aridnaja zona Straogo Sveta v pozdnem pleistosene I holocene (Arid zone of the Old World in the Late Pleistocene and Holocene). Bulletin All-Russian Geographic Society, 117: 16–23 (in Russian) (1985). Dregne, H. E., and Nan-Ting Chou. Global desertification dimensions and costs. In: Degradation and Restoration of Arid Lands (Dregne, H. E., Ed.). Lubbock, TX: Texas Tech. University (1992). FAO. FAO Agricultural Data. http://apps.fao.org/, United Nations Food and Agriculture Organization, Rome (2003). Last accessed June, 2003. Climate Change in Central Asia 47 Gladishev, A. I., and L. E. Rodin. Structure and distribution of phytomass of riverbed forest communities along the middle stretch of the River Amu-Daria (Turkmenian SSR). Botanicheskij Zurnal (Botanic Journal), 62: 3–14 (in Russian) (1977). Glantz, M. H. Creeping Environmental Problems and Sustainable Development in the Aral Sea Basin. Cambridge: Cambridge University Press (1999). Glazovsky, N. F. The Aral Sea basin. In: Regions at Risk: Comparisons of Threatened Environments (Kasperson, J. X., R. E. Kasperson, and B. L. Turner II, Eds.). Tokyo, New York, Paris: United Nations University Press (1995). Goudie, A. S. Deserts in a warmer world, pp. 1–29. In: Environmental Change in Drylands: Biogeographical and Geomorphological Perspectives (Millington, A. C., and K. Pye, Eds.). New York: Wiley (1994). Grünzweig, J., and C. Köerner. Growth and reproductive responses to elevated CO2 in wild cereals of the northern Negev of Israel. Global Change Biol., 6: 631–638 (2000). Guilmanov, T. G. Gross primary production of the true steppe in central Asia in relation to NDVI: Scaling up of CO2 fluxes. USDA Symposium on Natural Resource Management to Offset Greenhouse Gas Emissions, Raleigh, NC (2002). Hulme, M. Global land area historical monthly precipitation dataset (1900–1998). University of East Anglia, Climatic Research Unit, Norwich, United Kingdom http://www.cru.uea.ac.uk/∼mikeh/ datasets/global/ (1998). Last accessed May, 2003. IPCC. Climate Change: The Scientific Basis Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) (Houghton, J.T., Y. Ding, D .J. Griggs, M. Noguer, P. J. van der Linden, and D. Xiaosu, Eds.). Cambridge: Cambridge University Press (2001). Kes, A. S., E. D. Mamedov, S. O. Khondkaryan, G. N. Trofimov, and K.V. Kremenetsky. Stratigrafija i paleografija ravninnih oblastej Srednej Azii v pozdnem pleistocene i golocene (Plains of northern central Asia during the Late Pleistocene and Holocene: Stratigraphy and palaeogeography) (in Russian), pp. 82–87. In: Evolution of Landscapes and Climates of the Northern Eurasia (Velichko, A. A., Ed.). Moscow: Nauka Publishers (1993). Kharin, N., G., R. Tateishi, and I. G. Gringof. Use of NOAA AVHRR data for assessment of precipitation and land degradation in Central Asia. Arid Ecosys., 4: 25–34 (1998). Kirsta, B. T., and A. B. Rihlov. Antropogennije izmenenija klimata Murgabskogo i Tedgenskogo oasisov (Anthropogenic climate changes in Murghab and Tedgen oases), pp. 60–74. In: Specific Features of Water-Heat Regimes and Agroprognoses in Turkmenistan. Ashkhabat: Ilim Publishers (1988). Kogan, F. N. Application of vegetation index and brightness temperature for drought detection. Adv. Space Res., 15: 91–100 (1995). Lal, R., and J. Kimble. Pedogenic carbonates and the global carbon cycle, pp. 1–15. In: Global Climate and Pedogenic Carbonates (Lal, R., J. Kimble, H. Eswaran, and B. S. Stewart, Eds.). Boca Raton, FL: Lewis Publishers (2000). Lambin, E. Modelling and monitoring land-cover change processes in tropical regions. Prog. Phys. Geog., 21: 375–393 (1997). Lioubimtseva, E. Arid environments, pp. 267–283. In: Physical Geography of Northern Eurasia (Shahgedanova, M., Ed.). Oxford: Oxford University Press (2002). Lioubimtseva, E., and J. M. Adams. Carbon content in desert and semidesert soils in Central Asia, pp. 409–456. In: Agricultural Practices and Policies for Carbon Sequestration in Soil (Kimble, J. M., R. Lal, and R. F. Follett, Eds.). Boca Raton, FL: CRC Press Lewis Publishers (2002). Lioubimtseva, E., and J. M. Adams. Possible implications of increased carbon dioxide levels and climate change for desert ecosystems. Environmental Management, 33(4): 5388–5404 (2004). Lioubimtseva, E., B. Simon, H. Faure, L. Faure-Denard, and J. M. Adams. Impacts of climatic change on carbon storage in the Sahara-Gobi desert belt since the late glacial maximum. Global Planetary Change, 16–17: 95–105 (1998). Loaiciga, A. H. Climate change and ground water. Ann. Assoc. Am. Geog., 93: 30–41 (2003). Markov, K. V. Is Middle and Central Asia getting drier? Geografgiz, 24: 98–116 (1951). 48 E. Lioubimtseva and R. Cole Melillo, J. M., A. D. McGuire, D. W. Kicklighter, B. Moore III, C. J. Vorosmarty, and A. L. Schloss. Global climatic change and terrestrial net primary production. Nature, 363: 234–240 (1993). Micklin, P. P. Dessication of the Aral Sea: A water management disaster in the Soviet Union. Science, 241: 1170–1176 (1988). Middleton, N. J. The Aral Sea, pp. 497–510. In: Physical Geography of Northern Eurasia (Shahgedanova, M., Ed.). Oxford: Oxford University Press (2002). Molosnova T. I., O. I. Subbotina, and S. G. Chanysheva. Klimaticheskye posledstvija khozajstvennoj deyatelnosti v zone Aralskogo morya (Climatic effects of economic activity in the Aral Sea area) (in Russian). Leningrad: Gidrometeoizdat, Leningrad (1987). Nechaeva, N. T. (Ed.). Resursy biosphery pustin Srednei Azii i Kazakhstana (Biosphere Resources of Deserts in Central Asia and Kazakhstan) (in Russian). Moscow: Nauka Publishers (1984). Neronov V. V. Landshaftnije osobennosti vekovih izmenenij uvlaznennosti v yugo-vostochnom Turkmenistane (Landscape features of century changes in wetting of south-eastern Turkmenistan). Aridnije Ecosystemi, 3(6–7): 141–150 (in Russian) (1997). Nicholson, S. E., M. B. Ba, and C. J. Tucker. Desertification, drought and surface vegetation: An example from the West African Sahel. Bull. Am. Meteorol. Soc., 79: 816–829 (1998). Peterson, T. C., and R. S. Vose. An overview of the global historical climatology network temperature database. Bull. Am. Meteorol. Soc., 78: 2837–2849 (1997). Petrov, M. P. Deserts of the World. New York: John Wiley & Sons (1976). Population Reference Bureau (PRB). World population data sheet. Washington, DC (2002). Semenov, O. E. 1990. Ocenka ob’emov vinosov peska i soley c osushivshejsa chasti dna Aralskogo morja (Assessment of sand and salt redeposition from the dry part of the Aral Sea lake-bed), pp. 200–215. In: Hydrometeorological Problems of the Aral Sea Area (in Russian) (Chichasov, G. N., Ed.). Leningrad: Gidrometeoizdat (1990). Shiklomanov, I. A. Climate change, hydrology and water resources: The work of the IPCC, 1988–94, pp. 8–20. In: Impacts of Climate Change and Climate Variability on Hydrological Regimes (Van Dam, J. C., Ed.). Cambridge: Cambridge University Press (1999). Shnitnikov, A. V. Vnutrivekovaja izmenchivost komponentov obchej uvlaznennosti (Inter-centennial variability of general humidity components) (in Russian). Leningrad: Nauka Publishers (1969). Smith, S. D., T. E. Huxman, S. F. Zitzer, T. N. Charlet, D. C. Housman, J. S. Coleman, L. K. Fenstermaker, J. R. Seemann, and R. S. Nowak. Elevated CO2 increases productivity and invasive species success in an arid ecosystem. Nature, 408: 79–82 (2000). Tarasov, P. E. Evlutsia klimata i landshaftov Severnogo i centralnogo Kazakhstana (Climatic and landscape evolution of northern and central Kazakhstan) (in Russian). PhD thesis, Moscow State University, Moscow, Russia (1992). Tarasov, P. E., T. Webb III, A. A. Andreev, N. B. Afanas’eva, N. A. Berezina, L. G. Bezusko, T. A. Blyakharchuk, N. S. Bolikhovskaya, R. Cheddadi, M. M. Chernavskaya, G. M. Chernova, N. I. Dorofeyuk, V. G. Dirksen, G. A. Elina, L. V. Filimonova, F. Z. Glebov, J. Guiot, V. S. Gunova, S. P. Harrison, D. Jolly, V. I. Khomutova, E. V. Kvavadze, I. M. Osipova, N. K. Panova, I. C. Prentice, L. Saarse, D. V. Sevastyanov, V. S. Volkova, and V. P. Zernitskaya. Present-day and mid-Holocene biomes reconstructed from pollen and plant macrofossil data from the former Soviet Union and Mongolia. J. Biogeogr., 25: 1029–1053 (1998). Thornthwaite, C. W. An approach towards a rationale classification of climate. Geogr. Rev., 38: 55–94 (1948). United Nations Environmental Program (UNEP). World Atlas of Desertification (Middleton, N., and D. Thomas, Eds.). London: Edward Arnold for United Nations Environmental Program (1992). Varuschenko, S. I., A. N. Varuschenko, and R. K. Klige. Izmenenija rezima Kaspijskogo morja i besstochnih vodoemov v paleovremeni (Variations of the Caspian Sea regime and of closed lakes in palaeotimes) (in Russian). Moscow: Nauka Publishers (1987). Velichko, A. A., V. A. Klimanov, and A. V. Belyaev. Caspian Sea and Volga River 5.5 and 125 thousands years before present. Priroda, 3: 60–66 (in Russian) (1987). Voznesensky, V. L. Fotosyntez pustinnih rastenij (Photosynthesis of desert vegetation) (in Russian). Leningrad: Nauka Publishers (1977). Climate Change in Central Asia 49 Wang, G., and E. A. B. Eltahir. Biosphere-atmosphere interactions over West Africa. II: Multiple climate equilibria. Q. J. Roy. Meteor. Soc., 126: 1261–1280 (2000). Whitford, W. Ecology of Desert Systems. London: Academic Press. An Elsevier Science Imprint (2002). Woodward F. I., M. R. Lomas, and R. A. Betts. Vegetation-climate feedbacks in a greenhouse world. Philos. T. Roy. Soc. B, 353: 29–38 (1998). Zelensky, O. B. Ecologo-fisiologicheskije aspekti izuchenija fotosinteza (Eco-physiological aspects of photosynthesis research) (in Russian). Leningrad: Nauka Publishers (1977). Zinke P. J., A. G. Stangenburger, W. M. Post, W. R. Emmanuel, and J. S. Olson. Worldwide organic soil carbon and nitrogen data. Oak Ridge National Lab, U.S. Department of Energy, Environmental Sciences Division, Publication 2212 (1984). Zolotokrylin, A. N. The indicator of climate aridity (Indicator klimnaticheskoj aridnnosti). Arid Ecosystems, 8: 49–57 (in Russian with summary in English) (2002). Zolotokrylin, A. N. Klimaticheskoje opustinivanije (Climatic desertification) (in Russian). Moscow: Nauka Publishers (2003). Zolotokrylin, A. N., and L. V. Hmelevskaya. Atmosfernaja circulatzija i osadki v bassejne Arala v tekushem stoletii (Atmospheric circulation and precipitation in the Aral Sea area during the current century). Izvestija Russian Academy of Science, ser. Geography, 5: 30–33 (in Russian) (1999).