Over the past half century there has been a trend in numerous regions of the western United States toward a declining portion of the total annual streamflow occurring during the snowmelt season (April through July). Changes in the seasonality of discharge primarily reflect a shift in the seasonal distribution of precipitation. Years with an unusually large fraction of annual streamflow occurring during the spring snowmelt coincide with winters with unusually high precipitation. Years with an unusually small fraction of annual streamflow occurring during the spring snowmelt coincide with unusually low precipitation during the winter and unusually warm temperatures during the spring. The magnitude of the peak annual flood is sensitive to amount of winter precipitation and variations in spring and early summer temperatures. Large peak annual floods occur in years with high precipitation and low temperatures in the late winter and spring, which preserve the maximum snowpack. Small peak annual floods occur in years with low precipitation throughout the winter and high temperatures in the spring. During the period of gage record, peak annual flood magnitudes exhibit temporal variability. Extreme events in the peak annual flood record, particularly years of large snowmelt floods, have increased in frequency since 1960. Large floods during this time period occur in years with atypically cool temperatures in April and May, which would likely preserve the winter snowpack through the spring.

The Provo River drainage in the western end of the Uinta Mountains was glaciated repeatedly during the Pleistocene, and glacial deposits from the Smiths Fork and Blacks Fork glaciations (Pinedale and Bull Lake equivalents, respectively) are well preserved throughout the area. Reconstruction of the Smiths Fork ice extent based on air photo analysis and field mapping reveals that the broad upland surfaces in the Provo River drainage were covered by an ice field from which distributary glaciers emanated. This ice field also covered parts of the Weber and Bear River drainages to the north and the North Fork Duchesne drainage to the east. Equilibrium line altitudes for glaciers in the Provo River drainage were ∼2900 m a.s.l., consistent with previous studies which recognized a dramatic decrease in equilibrium line altitudes toward the western end of the range. End moraine sequences and hypsometric differences between glaciers in the Provo River drainage suggest that ice retreat rates likely differed considerably among the glaciers, reflecting variable dynamic responses to a similar climate forcing during deglaciation.

The headwaters of the Bear River drainage were occupied during the Last Glacial Maximum (LGM) by outlet glaciers of the Western Uinta Ice Field, an extensive ice mass (∼685 km²) that covered the western slope of the Uinta Mountains. A well-preserved sequence of latero-frontal moraines in the drainage indicates that outlet glaciers advanced beyond the mountain front and coalesced on the piedmont. Glacial deposits in the Bear River drainage provide a unique setting where both ¹⁰Be cosmogenic surface-exposure dating of moraine boulders and ¹⁴C dating of sediment in Bear Lake downstream of the glaciated area set age limits on the timing of glaciation. Limiting ¹⁴C ages of glacial flour in Bear Lake (corrected to calendar years using CALIB 5.0) indicate that ice advance began at 32 ka and culminated at about 24 ka. Based on a Bayesian statistical analysis of cosmogenic surface-exposure ages from two areas on the terminal moraine complex, the Bear River glacier began its final retreat at about 18.7 to 18.1 ka, approximately coincident with the start of deglaciation elsewhere in the central Rocky Mountains and many other alpine glacial localities worldwide. Unlike valleys of the southwestern Uinta Mountains, deglaciation of the Bear River drainage began prior to the hydrologic fall of Lake Bonneville from the Provo shoreline at about 16 ka.

We examine instrumental meteorological records to compare recent precipitation regimes in the eastern and western Uinta Mountains region of Utah. The comparison demonstrates that, although the summer monsoon contributes a higher proportion of annual precipitation in the east, the two regions are significantly correlated in terms of precipitation variations including summer precipitation. Major droughts, such as the 1930s Dustbowl event, the 1976–1977 event, and the 1987–1989 event, are largely typified by strong decreases in winter precipitation, although deficits can extend into summer. Droughts generally impact the entire region when they occur. Unlike the Southwest and the Pacific Northwest, year-to-year precipitation variability in the Uinta Mountains region does not appear correlated with the El Niño–Southern Oscillation or the Pacific Decadal Oscillation. However, severe prolonged droughts such as the 1976–1977 and 1986–1987 events are related to decreases in eastern Pacific Ocean sea surface temperatures. We extend the record of hydroclimatic variability for the Uinta Mountains by using tree-ring chronologies from Pinus edulis (two-needle pinyon) to reconstruct the summer Palmer Drought Severity Index (PDSI) back to A.D. 1405. The analysis demonstrates that extreme droughts (PDSI < −4) and extended multiannual to multidecadal arid periods (PDSI < 0 to <−2) are a recurrent feature of the Uinta hydroclimatic regime. Extreme droughts of PDSI < −4 typically occur two to five times per century, with an annual probability of occurrence of ∼4.4%. In the context of prolonged severe droughts, the 20th century enjoyed relatively moist conditions compared to the 17th, 18th, and 19th centuries. The most prominent of these earlier arid periods was an apparent ‘mega-drought’ between ca. A.D. 1625 and 1670 that is evident in prolonged depression of PDSI values in the Uinta Mountains region, decreased discharge of the Ashley River, and decreased precipitation in the adjacent Uinta Basin. There was a general depression of the Pacific Decadal Oscillation during this time, suggesting some linkage between conditions in the Pacific Ocean and prolonged aridity. Wavelet analysis demonstrates the presence of multidecadal variability in aridity, but the frequency and power of long-term modes of variability are inconsistent over the past 600 years.

Sediment cores were retrieved from 12 lakes in the southern Uinta Mountains ranging in elevation from 2960 to 3475 m. Organic content was determined by loss-on-ignition (LOI) at 1-cm intervals (n = 2850), corresponding to 20 to ∼100 yrs per sample. This data set was used to explore relationships between watershed variables and LOI records. Average LOI values are strongly correlated with lake elevation, elevation of the watershed, extent of late-lying snow and bare rock in the watershed, and the area of upstream lakes. Average LOI values are not significantly correlated with lake depth, or with lake or watershed area. The 12 LOI records can be visually divided into 3 groups with contrasting patterns: Steady, Trending, and Rising. Steady lakes have the lowest average LOI values, and are located in watersheds with the highest maximum elevations and the largest area of upstream lakes and late-lying snow. The most significant determinant on average LOI and LOI pattern is hydrologic through-flow as revealed by the configuration and number of inlets and outlets. The repetition of Steady, Trending, and Rising LOI patterns in different parts of the range, combined with contrasting LOI patterns in adjacent lakes, suggests that watershed characteristics strongly influence organic sedimentation.

Surface sediment recovered from 51 lakes in the Uinta Mountains of northeast Utah was analyzed for subfossil chironomid remains, and incorporated in a midge-based inference model for summer surface water temperature (SSWT). The lakes in the calibration set spanned elevation, depth, and summer surface water temperature ranges of 900 m, 12.7 m, and 11.3°C, respectively. Redundancy analysis (RDA) identified four variables, SSWT, depth, specific conductivity, and Al concentration, that could account for a statistically significant amount of variance in the chironomid distribution, with SSWT accounting for the largest amount of variance. The Uinta Mountain calibration set was merged with a previously developed calibration set from the Sierra Nevada, California, in order to develop a midge-based inference model for SSWT applicable to subfossil chironomid stratigraphies from the Great Basin. A variety of statistical approaches, such as weighted averaging (WA), weighted averaging-partial least squares (WA-PLS), and partial least squares (PLS) were used to assess model performance. The best inference model for SSWT, based on a 3-component WA-PLS approach, had robust performance statistics (r²_jack = 0.66, RMSEP = 1.4°C). The newly expanded inference model will enable more accurate estimates of late Pleistocene and Holocene thermal regimes and help address many outstanding questions relating to long-term and recent climate change in this region.

Twelve profiles of alpine soils associated with well-developed, but currently inactive, sorted polygons were investigated in the Uinta Mountains of northeastern Utah. The summit upland in the Uintas does not appear to have been glaciated, and these soils are considerably older than those located in lower elevation glacial valleys. Profiles of soils from the polygon centers reveal a dark, organic-rich surface horizon developed in loamy loess overlying a series of redder, sandy B horizons locally exhibiting strongly developed platey structure and pockets of coarser sediment. Irregular and broken horizons at depth reflect extensive cryoturbation during episodes when the sorted polygons are active. Overall morphology and profile quantities of weathering products in these soils are similar to those previously reported for alpine tundra soils in the Uintas; however, the cryoturbated horizons are limited to soils in the patterned ground. A developmental model for these soils emphasizes the combined role of pedogenic processes operating during interglaciations (accumulation of organic matter and loess, translocation of silt and clay, chemical weathering) and periods of cryoturbation (distortion of horizons, redistribution of weathering products within the solum). Outstanding questions include the timing and relative duration of cryoturbation episodes, the timing of loess deposition, and the overall age of the soils.

The dominant mechanisms of soil formation on a sequence of Smiths Fork, Blacks Fork, and Pre–Blacks Fork moraines in West Fork of Beaver Creek, Uinta Mountains, Utah, (equivalent to Pinedale, Bull Lake, and Pre–Bull Lake moraines of the Wind River Range, respectively) are clay translocation (argilluviation), increasing soil redness (rubification), and the accumulation of organic matter (melanization) and silt-sized particles. The quantity of clay-sized particles and degree of soil redness increase with soil age, but clay accumulation may plateau in the oldest soils. In contrast, the quantity of accumulated organic matter and abundance of silt-sized particles do not appear to correlate to soil age. The Smiths Fork moraine, interpreted to be MIS-2 in age, has two crests that have distinctly different amounts of clast weathering and soil development. The outer Smiths Fork crest displays weathering that is more comparable to that of the Blacks Fork moraine than to the inner Smiths Fork crest. This weathering contrast is related to an age difference between the two crests, but a precise chronology of the Smiths Fork moraines cannot be determined from these data.

This study examined the influence of snowmelt, vascular plants, grazing, substrates, and soil characteristics on the distribution of lichen communities along an alpine tundra ridge in the Uinta Mountains of Utah. Percent cover of lichens, rocks, snow, and vascular plants were estimated at 18 study sites along an altitudinal transect. Vascular plant cover and species diversity were greatest at the lower elevation sites, and differences in plant communities were related to differences in rock cover and grazing. Lichens showed a similar trend, with rock cover, grazing, vascular plants, and timing of snowmelt all defining community structure. We hypothesize that domestic sheep have dispersed fragments of two lichen species from western Wyoming to grazed sites along the study transect. Generally, terricolous and epiphytic lichens differed between the lower and upper sites in species composition and growth-form distribution. Distribution of lichen growth forms was positively correlated with increasing rock cover. Late snowmelt areas were also distinguished by a defined group of lichens.

The Uinta Mountains form a crossroads of forests and woodlands in the central Rocky Mountains. Although no tree species is endemic to the area, all species characteristic of the central Rocky Mountains are found there, and the ranges of several other species terminate in the Uinta Mountains and the surrounding area. The peninsula-like shape, east-west orientation, and complex terrain of the range create a wide variety of potential forest sites that contrast with other ranges in the central Rockies. As a result, the Uinta Mountains are home to sites of unexpectedly high tree species diversity. Throughout most of the range, vegetation is organized in predictable zones that are characteristic of the Intermountain West; the range exhibits excellent vegetation zonation. However, across much of the northern slope several important species are absent, resulting in unexpectedly low diversity and “missing” vegetation zones. In this paper we provide an overview of the forest ecology and biogeography of the Uinta Mountains and update the local model for vegetation zonation. We also consider some possible explanations for the unexpected vegetation patterns and identify opportunities for future research.

The Normalized Difference Vegetation Index (NDVI) derived from NOAA AVHRR Global Vegetation Index (GVI) for Lhasa area in the central Tibetan Plateau from 1985 to 1999 and its relationship with climate conditions (precipitation and temperature) are established in this study. Climate data from the Lhasa meteorological station provided by the Tibet Climate Data Center are used for this analysis. The NDVI-derived vegetation growth patterns show very strong seasonal cycles and interannual variations. The growing season length varies between years. The correlation between NDVI and precipitation (r = 0.75, P < 0.01) in Lhasa area is higher than the correlation between NDVI and temperature (r = 0.63, P < 0.01), suggesting that NDVI is more sensitive to precipitation than temperature in this semiarid climate zone. Furthermore, the time series of NDVI demonstrate a positive trend from 1985 to 1999, which means that the vegetation biomass present on land surface is increasing. This trend is strongly correlated to increased rainfall and temperature from mid-1980s to 1990s in the Lhasa area of the Tibetan Plateau.

Glacial retreat on the Tibetan Plateau and surrounding regions is characteristic since the 1960s and has intensified in the past 10 yr. The magnitude of glacial retreat is relatively small in the interior of the Tibetan Plateau and increases to the margins of the plateau, with the greatest retreat around the edges. Glacial retreat in this region is impacting the hydrological processes in the Tibetan Plateau and surrounding regions. The glacial retreat has caused an increase of more than 5.5% in river runoff from the plateau. In some areas, such as the Tarim River basin, the increase in river runoff is greater. Glacial retreat has also caused rising lake levels in the areas with large coverage of glaciers, such as the Nam Co Lake and Selin Co Lake areas. Rising lake levels are devastating grasslands and villages near the lakes.

Using long-lived Qilian juniper (Sabina przewalskii Kom.) in the middle Qilian Mountains, the temperature variations in the last 1000 yr were reconstructed. We find that the annual growth ring width and δ¹³C series mainly reflect variations in regional temperature. Except in May, warmer temperatures indicate greater growth over the period from December to April, and δ¹³C values in tree-rings are higher for years with higher temperature. The notable features in the temperature reconstruction are the occurrence of the Little Ice Age from A.D. 1600 to 1880 and the abrupt warming over the end of past millennia. The comparison of our chronology to a Northern Hemispheric temperature proxy shows that our tree-ring data will facilitate intercontinental differentiation of large-scale synoptic climate variability.

A 107-cm-long lake core was drilled in South Hongshan Lake (35°10′N, 80°04′E, 5060 m a.s.l.) shows 150 yr of environmental change as inferred from ostracoda assemblages. Four species of ostracoda, which belong to four genera, have been identified. The ostracoda distribution in the core can be divided into six ostracoda assemblages as follows: OA1—Ilyocypris biplicata–Limnocythere inopinata assemblage; OA2—Limnocythere inopinata–Leucocythere mirabilis assemblage; OA3—Leucocythere mirabilis–Limnocythere inopinata assemblage, in which dominant species is Limnocythere inopinata; OA4—Nearly ostracoda free; OA5—Eucypris inflata–Limnocythere inopinata assemblage; and OA6—Limnocythere inopinata changes from dominant to sole species. These ostracoda assemblages, together with other proxies, imply the following environmental sequence for the past 150 yr in the study area. Shallow moving water appears in A.D. 1850–1884, followed by a warm-humid climate in 1884–1922. Lake level decreased and water temperature supported maximum ostracoda growth in 1922–1946, followed by cooling conditions in 1946–1960. From 1960 to 1980, declining lake level is closely linked with local precipitation. The period since 1982 is characterized by less precipitation and continuous aridity under warming climatic conditions.

Annual accumulation records covering the period A.D. 1952–1998 were reconstructed using a 29.5-m ice core from the col of the Lanong Glacier (5850 m a.s.l.) on the eastern saddle of Mt. Nyainqentanglha, southern Tibetan Plateau. Using NCEP/NCAR Reanalysis data, we explore the relationships between this ice-core accumulation record and primary components of the climate system. Linear correlation analysis between annual accumulation and climate components for the 47-yr overlap period indicates that annual accumulation variations are closely correlated with sea-surface and 500-mb air temperature over the North Indian Ocean and atmospheric circulation (surface pressure and geopotential height) over Asia (r > 0.34, P < 0.01). An intensification of atmospheric circulation and increase of sea-surface and air temperatures, resulting in intensified moisture availability and moisture transport, have been a major cause for the increase of ice-core accumulation over the Mt. Nyainquentanglha region since the 1980s.

Based on the Guliya, Dunde, and Dasuopu ice cores and direct observations, we investigated the spatial and temporal variations in precipitation on the Tibetan Plateau over the past 500 yr. The variations in accumulation rates showed significant periodicities of 12.7, 7.6, 6.2, 5.4, 4.4, and 2.1 yr in the Guliya ice core, 9.5, 6.8, 5.7, and 2.1 yr in the Dunde ice core, and 12.3, 7.5, 6.3, 5.3, and 2.4 yr in the Dasuopu ice core. The periodicities displayed in these three ice core records are similar and correspond to the periodicities of the Quasi-Biennial Oscillation, the Southern Oscillation, the North Atlantic Oscillation, and the sunspot cycle. However, the accumulation rate from the Guliya and Dunde ice cores exhibited a generally decreasing trend, while the records from the Dasuopu ice core show a generally increasing trend over the entire period of interest. Our study also indicates that there is a strong negative correlation between the accumulation rates in the ice cores from the northern and southern Tibetan Plateau, especially on climatological (multidecadal or longer) time-scales. Modern meteorological observation data suggest that a dividing line between the northern and southern Tibetan Plateau with respect to variations in precipitation is located at ∼32–33°N. This dividing line coincides with other atmospheric, geographical, geological, and geophysical discontinuities. This suggests that interactions among these phenomena might help to understand the spatial patterns of climate over the Tibetan Plateau.

Foliar δ¹³C values measured in 101 samples from 13 sites in northern Tibet averaged amplitude −26.9‰, and were higher than those of other mountain regions in the world. C₄ plants were found at 4161 m, higher than C₄ species have been found before. The foliar δ¹³C values increased with altitude; however, the amplitude of increase was dependent on species. Furthermore, significantly higher δ¹³C values were found in plants grown in the southern than the northern Tanggula Mountains, a difference ascribed to precipitation.

Monitoring of permafrost along the Qinghai-Tibet (Xizang) Highway shows that there is a large difference in the response of permafrost to climate change and to engineering construction. The change in cold (<−1.5°C) permafrost is greater than that in warm (≥−1.5°C) permafrost under the effect of climate change, while the cold permafrost is less sensitive to the disturbances from engineering activities. However, warm permafrost is very sensitive to both climate warming and the impacts from engineering construction. This is because engineering construction has more immediate and direct impacts on the thermal and moisture regimes of underlying permafrost, and consequently greater influence than climate change during the first few years after engineering construction. Assuming constant annual rates of warming, the surface of cold permafrost would approach the warming due to engineering construction in 50 yr, while it would take about 20 yr in areas with warm permafrost. At a depth of 6 m, the temperature rise under engineered surfaces would be reached within 20 and 5–8 yr in cold and warm permafrost, respectively. Therefore, the warming immediately following disturbances of engineering construction would occur naturally in a few years under warm permafrost, but it would take decades for cold permafrost to have the similar thermal effects. Therefore, climate change will have more direct and immediate impacts on the thermal regime of warm permafrost and on the stability and reliability of engineering infrastructures above warm permafrost.

Observations at the Shiquanhe and Gaize meteorological stations provide data for analysis of δ¹⁸O and δD variations in precipitation for the Ngari (Ali) region, western Tibetan Plateau. Temperature controls δ¹⁸O in precipitation in this area. δ¹⁸O in precipitation positively correlates with air temperature at the Shiquanhe and Gaize stations, especially for precipitation weighted monthly mean δ¹⁸O. The δ¹⁸O – T correlation gradually strengthens from south to north across the western Tibetan Plateau and adjacent regions, with gradual weakening of southwest monsoon activity. The strongest correlation is found at Hetian. There is a poor correlation between δ¹⁸O and air temperature in the south at New Delhi because the moisture derives predominantly from the Indian Ocean in summer. The Ngari region exhibits a close relation between δD and δ¹⁸O in precipitation samples, similar to stations in adjacent regions and the global meteoric water line. The summer seasonal averaged deuterium excess (d) values increase gradually from south to north across western Tibetan and adjacent areas, resulting from southwest monsoon activity gradually weakening to the north.

High-resolution soil moisture, temperature, and precipitation data from the northern part of the Tibetan Plateau provide the basis for analyzing the cycling of water between the land surface and atmosphere. Data analyzed come from the Intensive Observation Period (IOP) of the GEWEX (Global Energy and Water Cycle Experiment) Asian Monsoon Experiment (GAME) on the Tibetan Plateau (GAME-Tibet). Observations from July to August 1998 show that evaporation from flat land surfaces was 177 mm on the south side of the Tanggula Mountains, and 73 mm on the north side. These represent about 73% and 58%, respectively, of the precipitation in the same period. Evaporation not only transports considerable water but also considerable energy from the land surface to the atmosphere, which can slow the rising of soil temperatures. Differences in the evaporation between the south and north sides of Tanggula Mountains is mainly caused by differences in precipitation.

With mesoscale data from a high-resolution numerical model, this paper analyzes the impact of the complex mesoscale terrain at the eastern edge of the Tibetan Plateau on the formation and development of a local severe storm. The result shows that the dynamic blocking effect of the Tibetan Plateau terrain affects the moisture transfer channel in this heavy rain scenario and brings about the formation of a strong water-vapor convergence center in northwest Sichuan and the upper branch of Huang He (Yellow River). The terrain structure of the east side of the Tibetan Plateau places a high energy tongue and energy front in the lower layer of the troposphere of Sichuan Basin and helps establish unstable potential energy stratification in the lower troposphere of the Sichuan Basin. The accumulation of water vapor in the lower troposphere in the Sichuan Basin is the major reason for the establishment of unstable potential energy stratification. The steep terrain of the east side of Tibetan Plateau strengthens the ascendant motion. The strongest updraft movement occurred in the convergence area of the vertical shear of east and west wind and the steep landform, stimulating the unsteady release of energy and rapid development of the strong convection. The process is also accompanied by a mesoscale vortex in the east side of the Plateau. The most significant thermal and dynamic feature of this heavy rain scenario is that high temperature, high humidity, and strong vorticity columns appear only in the lower troposphere, which is very different from Mei-Yu. (“Mei-Yu” in Chinese and “Baiu” in Japanese refers to the frontal precipitation caused by Mei-Yu front, a persistent east-west zone of disturbed weather during early summer which is quasi-stationary and stretches from the east China coast, across Taiwan, and eastward into the Pacific Ocean south of Japan.)

By using radiosonde data in Sichuan Province and Chongqing Municipality of China during May–September from 1982 to 2002, the meteorological significance and evolution patterns of the atmospheric boundary layer (ABL) wind on the eastern edge of the Tibetan Plateau are analyzed. Results show that the ABL wind at Chengdu near the eastern edge of the Tibetan Plateau varies with regularity. Because of the interaction between the circulation and the topography, the wind field alternates between northeast and southwest winds. When northeast ABL winds prevail at Chengdu, the ABL in the Sichuan Basin maintains a cyclonic flow field and corresponds with heavy rain in the Sichuan Basin. When southwest winds prevail, the ABL maintains an anticyclonic flow field and corresponds with rainless, fine weather in Sichuan Basin. With the northeast-southwest–trending topography between the Tibetan Plateau and the Sichuan Basin, the dynamic trigger of the ABL at Chengdu is a very important cause of occurrence and development of severe, convective weather and heavy rain in the Sichuan Basin. The Chengdu station is the key weather station in the Sichuan Basin for weather prediction and understanding physical mechanisms.

The soil thermal regime of the Tibetan Plateau is modeled by applying a one-dimensional heat transfer model with phase change. The two main forcing variables are surface air temperature, from the ERA-40 reanalysis, and snow depth, derived from passive microwave satellite data. Daily fields of soil temperature are simulated, ranging from the soil surface down to 30 m depth, and the horizontal grid cell resolution is 25 km × 25 km. Results are presented for three different soil moisture regimes. The trend analysis is based on daily fields of active-layer depth (ALD) for the period January 1980 through December 2001. Significant positive ALD trends for all Tibetan permafrost regions are simulated in response to positive air temperature trends, with the strongest trend for the northern Tibetan Plateau ( 1.4 cm yr⁻¹). Significant trends can reach 4 cm yr⁻¹ locally. The day of year when ALD was reached shows strong interannual variation, and significant trends occur for smaller areas than for ALD. As an application, the active-layer deepening is presented along the tracks of the Qinghai-Tibet railroad line that has recently been completed.

Significant interaction occurs between ecosystem physiological processes and climate. Studying this interaction is beneficial for understanding dynamics of climate change as well as forecasting future climate change. On the Qinghai-Xizang Plateau, the highest plateau in the world, interaction between ecosystem physiological processes and climate affect mid-levels of the atmosphere, so the study of this interaction has a special significance. We use two models, a carbon cycle model (CCM3) and a land surface model (LSM), to simulate ecosystem carbon cycle characteristics over the Tibetan Plateau and its influence on climate. The CO₂ flux varies seasonally with ecosystem physiology processes on the Plateau: fluxes are highest in summer and lowest in winter. The seasonal variation of vegetation net CO₂ flux shows that vegetation is an atmospheric carbon sink during most of the year, except in winter. This means that vegetation could weaken the greenhouse effect, which is important in terms of global warming. The land ecosystem is a weak carbon source from October to April, and it is a carbon sink from May to September (especially between June and August). The Tibetan Plateau CO₂ fluxes vary spatially. The fluxes are highest over the southwest and southeast boundary areas and the northeast region of the Plateau in summer, and are lowest in the middle and northwest regions in winter. The interaction of CO₂ flux and temperature shows that higher temperatures increase vegetation photosynthesis and all respiration. The abrupt increase in land ecosystem physiological processes with increasing temperature indicates that any warming due to increased atmospheric CO₂ caused by human activity will be weakened by the land ecosystem over the Tibetan Plateau.