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1.
Elevation dependency of climate change signals has been found over major mountain ranges such as the European Alps and the Rockies, as well as over the Tibetan Plateau. In this study we examined the temporal trends in monthly mean minimum temperatures from 116 weather stations in the eastern Tibetan Plateau and its vicinity during 1961–2006. We also analyzed projected climate changes in the entire Tibetan Plateau and its surroundings from two sets of modeling experiments under future global warming conditions. These analyses included the output of the NCAR Community Climate System Model (CCSM3) with approximately 150 km horizontal resolution for the scenario of annual 1% increase in atmospheric CO2 for future 100 years and physically-based downscaling results from the NCAR CAM3/CLM3 model at 10' × 10' resolution during three 20-year mean periods (1980–1999, 2030–2049 and 2080–2099) for the IPCC mid-range emission (A1B) scenario. We divided the 116 weather stations and the regional model grids into elevation zones of 500 m interval to examine the relationship of climatic warming and elevation. With these corroborating datasets, we were able to confirm the elevation dependency in monthly mean minimum temperature in and around the Tibetan Plateau. The warming is more prominent at higher elevations than at lower elevations, especially during winter and spring seasons, and such a tendency may continue in future climate change scenarios. The elevation dependency is most likely caused by the combined effects of cloud-radiation and snow-albedo feedbacks among various influencing factors.  相似文献   

2.
Most general circulation models (GCMs) project that climate will be warmer in the 21st century, especially in high latitudes. Climate warming will induce permafrost degradation, which would have great impacts on hydrology, ecosystems and soil biogeochemistry, and could destabilize the foundations of infrastructure. In this study, we simulated transient changes of permafrost distribution in Canada in the 21st century using a process-based permafrost model driven by six GCM-generated climate scenarios. The results show that the area underlain by permafrost in Canada would be reduced by 16.0–19.7% from the 1990s to the 2090s. This estimate was smaller than equilibrium projections because the ground thermal regime was in disequilibrium at the end of the 21st century and permafrost degradation would continue. The simulation shows significant permafrost thaw from the top: On average for the area where permafrost exists in all the years during 1990–2100, active-layer thickness increased by 0.3–0.7 m (or 41–104%), the depth to permafrost table increased by 1.9–5.0 m, and the area with taliks increased exponentially. Permafrost was also thawed from the bottom in southern regions.  相似文献   

3.
Cryospheric change in China   总被引：16，自引：0，他引：16  
This paper provides an overview of the current status of the cryosphere in China and its changes. Up-to-date statistics of the cryosphere in China are summarized based on the latest available data. There are 46,377 glaciers in China, covering an area of 59,425 km2. The glacier ice reserve is estimated to be about 5600 km3 and the annual glacier runoff is about 61.6 × 109 m3. The continuous snow cover extent (> 60 days) in China is about 3.4 × 106 km2 and the maximum water equivalent is 95.9 × 109 m3 yr− 1. The permafrost area in China is about 1.72 × 106 km2. The total ground ice reserve on the Qinghai–Tibetan Plateau is estimated to be about 10,923 km3. Recent investigations indicated that glacier areas in China have shrunk about 2–10% over the past 45 yr. Total glacier area has receded by about 5.5%. Snow mass has increased slightly. Permafrost is clearly degrading, as indicated by shrinking areas of permafrost, increasing depth of the active layer, rising of lower limit of permafrost, and thinning of the seasonal frost depth. Some models predict that glacier area shrinkage could be as high as 26.7% in 2050, with glacier runoff increasing until its maximum in about 2030. Although snow mass shows an increasing trend in western China, in eastern China the trend is toward decreasing snow mass, with increasing interannual fluctuations. Permafrost degradation is likely to continue, with one-third to one-half of the permafrost on the Qinghai–Tibetan Plateau anticipated to degrade by 2100. Most of the high-temperature permafrost will disappear by then. The permafrost in northeastern China will retreat further northward.  相似文献   

4.
We utilize a regional climate model with detailed land surface processes (RegCM2) to simulate East Asian monsoon climates at 0 ka, 6 ka and 21 ka BP, and evaluate the changes in hydrology process, including vapor transportation, precipitation, evapotranspiration and runoff in the eastern and western China during these periods. Results indicate that the Tibetan Plateau climate presents a wet–cold status during the LGM while it exhibits a wet–warm climate at 6 ka BP. The LGM wetter climate over the Tibetan Plateau mainly results from the increased vapor inflow through its south boundary, while the increase in the vapor import over the Tibetan Plateau at 6 ka BP mostly sources from its west boundary. The increase in the LGM runoff over the Tibetan Plateau is mainly caused by the decrease in evapotranspiration, while the increase in runoff at the 6 ka BP mainly by the enhanced precipitation. Eastern China (including southern China) presents a dry status during the LGM, which precipitation and runoff decreases significantly due largely to weakened Asian summer monsoon that results in the decreased vapor inflow through the south boundary of eastern China. The variation pattern in the hydrological cycle in eastern China is contrary to that in western China during the LGM. The increase in precipitation and runoff at 6 ka BP in eastern China is tightly related to the strong Asian summer monsoon that leads to increased vapor import through the south boundary. Long term decrease trend in precipitation and runoff in northern China since the last 20 000 years may be attributed to the steady increase in vapor export through the east boundary as a result of the changes of East Asian monsoon and the adjustments of local atmospheric circulations in this area.  相似文献   

5.
The occurrence of permafrost in bedrock in northern Fennoscandia and its dependence on past and presently ongoing climatic variations was investigated with one- (1D) and two-dimensional (2D) numerical models by solving the transient heat conduction equation with latent heat effects included. The study area is characterized by discontinuous permafrost occurrences such as palsa mires and local mountain permafrost. The ground temperature changes during the Holocene were constructed using climatic proxy data. This variation was used as a forcing function at the ground surface in the calculations. Several versions of the present ground temperature were applied, resulting in different subsurface freezing–thawing conditions in the past depending on the assumed porosity and geothermal conditions.Our results suggest that in high altitude areas with a cold climate (present mean annual ground temperature between 0°C and −3°C), there may have been considerable variations in permafrost thickness (ranging from 0 to 150 m), as well as periods of no permafrost at all. The higher is the porosity of bedrock filled with ice, the stronger is the retarding effect of permafrost against climatic variations.Two-dimensional models including topographic effects with altitude-dependent ground temperatures and slope orientation and inclination dependent solar radiation were applied to a case of mountain permafrost in Ylläs, western Finnish Lapland, where bedrock permafrost is known to occur in boreholes to a depth of about 60 m. Modelling suggests complicated changes in permafrost thickness with time as well as contrasting situations on southern and northern slopes of the mountain.Extrapolating the climatic warming of the last 200 years to the end of the next century when the anticipated increase in the annual average air temperature is expected to be about 2 K indicates that the permafrost occurrences in bedrock in northern Fennoscandia would be thawing rapidly in low-porosity formations. However, already a porosity of 5% filled with ice would retard the thawing considerably.  相似文献   

6.
Understanding of past climatic variability over the Tibetan Plateau is still limited because of the lack of long-term climatic records. Here we reconstruct the mean summer (June–August) minimum temperature for the past 379 years based on tree-ring data in the source region of the Yangtze River. This reconstruction successfully captures recent abrupt climatic changes and agrees in general with other temperature reconstructions for the Tibetan Plateau on a decadal timescale. The cold and warm periods coincide with documented glacier advances and retreats on the east and southeast Tibetan Plateau. The interval 1816–22 is among the coldest periods in the reconstruction and may be related to the influence of the Tambora eruption in Indonesia in 1815. Comparisons with other paleoclimatic proxies imply a high degree of confidence for our reconstruction and its indicative power for a large-scale climate variability on the Tibetan Plateau.  相似文献   

7.
Permafrost warming in the Tien Shan Mountains, Central Asia   总被引：4，自引：0，他引：4  
The general features of alpine permafrost such as spatial distribution, temperatures, ice content, permafrost and active-layer thickness within the Tien Shan Mountains, Central Asia are described. The modern thermal state of permafrost reflects climatic processes during the twentieth century when the average rise in mean annual air temperature was 0.006–0.032 °C/yr for the different parts of the Tien Shan. Geothermal observations during the last 30 yr indicate an increase in permafrost temperatures from 0.3 °C up to 0.6 °C. At the same time, the average active-layer thickness increased by 23% in comparison to the early 1970s. The long-term records of air temperature and snow cover from the Tien Shan's high-mountain weather stations allow reconstruction of the thermal state of permafrost dynamics during the last century. The modeling estimation shows that the altitudinal lower boundary of permafrost distribution has shifted by about 150–200 m upward during the twentieth century. During the same period, the area of permafrost distribution within two river basins in the Northern Tien Shan decreased approximately by 18%. Both geothermal observations and modeling indicate more favorable conditions for permafrost occurrences and preservation in the coarse blocky material, where the ice-rich permafrost could still be stable even when the mean annual air temperatures exceeds 0 °C.  相似文献   

8.
Permafrost and climatic change in China   总被引：8，自引：0，他引：8  
The permafrost area in China is about 2.15×106 km2, and is generally characterized by altitudinal permafrost. Permafrost in China can be divided into latitudinal and altitudinal types, the latter can be further divided into plateau and alpine permafrost. Altitudinal permafrost also can be divided into five thermal stability types. The permafrost environment has changed significantly since the Late Pleistocene. In northeastern China, the southern limit of permafrost extended to 41–42°N during the last glaciation maximum; in the Holocene megathermal, it retreated northward. The ice wedges and permafrost formed during the Late Pleistocene are still present in the northern part of the Da-Xing'anling Mountains. The inactive ice wedges at Yitulihe indicate a cooling and subsequent permafrost expansion during the Late Pleistocene. The lower limit of altitudinal permafrost in western China has elevated from 800 to 1500 m since the last glaciation maximum. Compared with that in northern Europe and North America, latitudinal permafrost in northeastern China is less sensitive to climatic warming, but altitudinal permafrost, especially permafrost on the Qinghai–Tibet Plateau (QTP), is sensitive to climatic warming. Since the early 20th century, significant permafrost degradation has occurred and is occurring in most permafrost regions in China. Due to the combined influence of climatic warming and increasing anthropogenic activities, substantial retreat of permafrost is expected on the QTP and in northeastern China during the 21st century. Permafrost degradation has and will cast great influence on engineering construction, water resources and environments in the cold regions of China. The wetlands in the cold regions of China emit significant amounts of CH4 and N2O to the atmosphere and uptake atmospheric CO2 at a considerable rate, which might contribute to the global atmospheric carbon budget and feedback to climatic systems. However, uncertainties about permafrost changes, rates of changes and their environmental impacts are still large and call for intensive studying.  相似文献   

9.
Flood/drought series during the past 1000 yrs in the Yangtze Delta, China, was reconstructed based on historical documents and local chronologies. Continuous wavelet transform was applied to detect the periodicity and variability of the flood/drought series. Research results indicate that: (1) Larger fluctuations of climatic changes in the Tibetan Plateau result in higher wavelet variance of flood/drought in the Yangtze Delta, for example, during 1400–1700, the proxy indicators indicate that the annual temperature in Tibet experienced larger variability and that this time interval exactly corresponds to the time when the higher and significant wavelet variance occurred; (2) Periods featured by colder temperature in the Tibetan Plateau usually correspond to periods characterized by higher wetness with higher probability of flood events; (3) Variability of heating features of the Tibetan Plateau exerted great influences on intensity and onset of Indian monsoon and south Asian summer monsoon, and these atmospheric activities are in direct connection with precipitation in Eastern China. Current global warming may alter the snow mass of Tibetan Plateau and then alters the heating features of Tibetan Plateau, which may in turn impact flood/drought conditions in the Yangtze Delta.  相似文献   

10.
The growth of two high-elevation inland lakes (at 4600 m) was analyzed using satellite imagery (2000–2005) and data were collected over the last decade (1997–2006) at a plateau meteorological station (at 4820 m) and stream gauging data from a station (at 4250 m) in central Tibet. We examined the lake water balance responses to meteorological and hydrological variables. The results show that the lake areas greatly expanded by a maximum of 27.1% (or 43.7 km2) between 1998 and 2005. This expansion appears to be associated with an increase in annual precipitation of 51.0 mm (12.6%), mean annual and winter mean temperature increases of 0.41 °C and 0.71 °C, and an annual runoff increase of 20% during the last decade. The changes point to an abrupt increase in the annual precipitation, mean temperature and runoff occurring in 1996, 1998 and 1997, respectively, and a decrease in the annual pan evaporation that happened in 1996. The timing of lake growth corresponds closely with abrupt increases in the annual precipitation and runoff and with the decrease in the annual evaporation since the mid-1990s. This study indicates a strong positive water balance in these permafrost highland lakes, and provides further evidence of lake growth as a proxy indicator of climate variability and change.  相似文献   

11.
The history (45–0 ka BP) of the aquatic vegetation composition of the shallow alpine Lake Luanhaizi from the NE Tibetan Plateau is inferred from aquatic plant macrofossil frequencies and aquatic pollen and algae concentrations in the sediments. C/N (range: 0.3–100), δ13C (range: −28 to −15‰), and n-alkane measurements yielded further information on the quantitative composition of sedimentary organic matter. The inferred primary production of the former lake ecosystem has been examined in respect of the alternative stable state theory of shallow lakes [Scheffer, M., 1989. Alternative stable states in eutrophic, shallow freshwater systems: a minimal model. Hydrobiological Bulletin 23, 73–83]. Switches between clear and turbid water conditions are explained by a colder climate and forest decline in the catchment area of Lake Luanhaizi. The macrofossil-based reconstruction of past water depth and salinity ranges, as well as other organic matter (OM) proxies allowed climatic inferences of the summer monsoon intensity during the late Quaternary. Around 45 ka BP, conditions similar to or even moister than present-day climate occurred. The Lake Luanhaizi record is further evidence against an extensive glaciation of the Tibetan Plateau and its bordering mountain ranges during the Last Glacial Maximum. Highest lake levels and consequently a strong summer monsoon are recorded for the early Holocene period, while gradually decreasing lake levels are reconstructed for the middle and late Holocene.  相似文献   

12.
The Chinese Loess Plateau (CLP) comprises an extensive record of eolian deposition that contains important information about climate change. The objective of this study is to investigate if mineralogy can provide more insight into the long-term evolution of the East Asian monsoon. Comparisons between mineralogy and other paleoclimatic records (grain size and magnetic susceptibility) from the CLP have been made to evaluate the efficacy of mineralogy as a paleoclimatic tool.Here we present data from a mineralogical study of a red clay–loess sequence at Lingtai, central Chinese Loess Plateau. Changes related to source area(s), transport processes and weathering regime over time are recorded in mineral variation.Higher average concentrations of kaolinite, chlorite and quartz in the red clay, together with abrupt changes in relative mineral abundances across the red clay–loess boundary suggest a change of source area at 2.6 Ma. From 2.6 Ma to about 1.7 Ma the summer monsoon influence increases, destroying chlorite and contributing fine illite particles to the sediment. At around 1.7 Ma the mineralogy becomes relatively constant, suggesting that the monsoon was fairly stable during this period. At 0.7–0.5 Ma an increase of both summer monsoon and winter monsoon activity is inferred from illite, kaolinite, chlorite and plagioclase concentrations. Over the last 0.5 Ma mineralogy suggests an aridification of source area(s) as chlorite and plagioclase concentrations increase where illite concentration decreases. The last major change occurred around 0.07 Ma and indicates reducing summer monsoon influence as chlorite and quartz concentrations increase and illite concentration, as well as the < 2 μm size fraction, decreases. The mineralogical trends and differences between loess and paleosols units suggest different source areas in the last 0.5 Ma.  相似文献   

13.
The climatological signal of δ18O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ18O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ18O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ18О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP.  相似文献   

14.
Climate changes and recent glacier behaviour in the Chilean Lake District   总被引：1，自引：1，他引：0  
Atmospheric temperatures measured at the Chilean Lake District (38°–42°S) showed contrasting trends during the second half of the 20th century. The surface cooling detected at several meteorological stations ranged from − 0.014 to − 0.021 °C a− 1, whilst upper troposphere (850–300 gpm) records at radiosonde of Puerto Montt (41°26′S/73°07′W) revealed warming between 0.019 and 0.031 °C a− 1. Regional rainfall data collected from 1961 to 2000 showed the overall decrease with a maximum rate of − 15 mm a− 2 at Valdivia st. (39°38′S/73°05′W). These ongoing climatic changes, especially the precipitation reduction, seem to be related to El Niño–Southern Oscillation (ENSO) phenomena which has been more frequent after 1976. Glaciers within the Chilean Lake District have significantly retreated during recent decades, in an apparent out-of-phase response to the regional surface cooling. Moreover, very little is known about upper troposphere changes and how they can enhance the glacier responses. In order to analyse their behaviour in the context of the observed climate changes, Casa Pangue glacier (41°08′S/71°52′W) has been selected and studied by comparing Digital Elevation Models (DEMs) computed at three different dates throughout the last four decades. This approach allowed the determination of ice elevation changes between 1961 and 1998, yielding a mean thinning rate of − 2.3 ± 0.6 m a− 1. Strikingly, when ice thinning is computed for the period between 1981 and 1998, the resulting rate is 50% higher (− 3.6 ± 0.6 m a− 1). This enhanced trend and the related area loss and frontal retreat suggests that Casa Pangue might currently be suffering negative mass balances in response to the upper troposphere warming and decreased precipitation of the last 25–30 yr, as well as debris cover would not prevent the glacier from a fast reaction to climate forcing. Most of recent glaciological studies regarding Andean glaciers have concentrated on low altitude changes, namely frontal variations, however, in order to better understand the regional glacier changes, new data are necessary, especially from the accumulation areas.  相似文献   

15.
Seasonal snow covers the tundra surface for up to nine months of each year on the Alaskan North Slope. Variations in the snow thickness could strongly influence the thermal regime of the underlying soil and permafrost, and the surface energy balance. The impacts of increases and decreases in the tundra snow thickness on the thermal regime of snow surface, active layer, and permafrost, and on the conductive heat flow to the atmosphere were investigated numerically, by using an improved surface energy balance approach based one-dimensional heat transfer model. The baseline inputs for the numerical model are mean daily meteorological data and surface albedos collected at Barrow, Alaska from 1995 through 1999. Based on a study for the long-term mean daily maximum and minimum snow thickness distributions at Barrow in the snow season of 1948 through 1997, a snow thickness factor was defined and five simulation cases were run for the snow season of 1997–1998 by changing the snow thickness factor. The modeled results indicate that changes in snow thickness have significant impacts on ground thermal regimes and conductive heat flow to the atmosphere. Decreasing the snow thickness by 50% led to the maximum ground temperature decrease of 1.48 °C at 0.29 m depth, and 0.72 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December increase of 4.3 Wm− 2. Increasing the snow thickness by 50% resulted in the maximum ground temperature increase of 1.44 °C at 0.29 m depth, and 0.66 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December decrease of 1.57 W m− 2. On an annual basis, variation in the snow thickness by 50%, the ground temperature variations of more than 0.25 °C occurred as deep as 8.0 m below the ground surface. The modeled results also show that changes in snow thickness have a relatively small influence on the snow surface temperature.  相似文献   

16.
New paleovegetation and paleoclimatic reconstructions from the Sierra Madre Occidental (SMO) in northwestern Mexico are presented. This work involves climate and biome reconstruction using Plant Functional Types (PFT) assigned to pollen taxa. We used fossil pollen data from four Holocene peat bogs located at different altitudes (1500‑2000 m) at the border region of Sonora and Chihuahua at around 28° N latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.; Ortega-Rosas, C.I., Peñalba, M.C., Guiot, J. Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico. Submitted for publication of Palaeobotany and Palynology). The closest modern pollen data come from pollen analysis across an altitudinal transect from the Sonoran Desert towards the highlands of the temperate SMO at the same latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.). An additional modern pollen dataset of 400 sites across NW Mexico and the SW United States was compiled from different sources (Davis, O.K., 1995. Climate and vegetation pattern in surface samples from arid western U.S.A.: application to Holocene climatic reconstruction. Palynology 19, 95–119, North American Pollen Database, Latin-American Pollen Database, personal data, and different scientific papers). For the biomization method (Prentice, I.C., Guiot, J., Huntley, B., Jolly, D., Cheddadi, R., 1996. Reconstructing biomes from paleoecological data: a general method and its application to European pollen data at 0 and 6 ka. Climate Dynamics 12, 185–194), we modified the pollen-PFT and PFT-biomes assignation of Thompson and Anderson (Thompson, R.S., Anderson, K.H., 2000. Biomes of western North America at 18,000; 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data. Journal of Biogeography 27, 555–584) for a better representation of the modern vegetation of NW Mexico. The biome reconstruction method was validated with the modern pollen sites and applied to the fossil sites. Our results show that, during the early Holocene, a cool conifer forest extended at least down to 1700 m, while today this biome is present above 2000 m in the Chihuahua state. The Younger Dryas event was recorded in one site with cold and dry conditions. The reconstructed annual temperature for this period was 3°–6 °C colder than today, and annual precipitation was 250 mm lower than at present (900 mm/yr). The middle Holocene after 9200 cal yr BP was marked by a warming trend, reaching temperatures 2 °C warmer than today at 7000 cal yr BP, and by the installation of a warm mixed forest, the present day biome, at 1700 m elevation, while at higher elevations (1900 m) the cool conifer forest was still present. Summer precipitation was 200 mm/yr above the early Holocene values, suggesting that monsoon-like conditions strengthened since 9200 cal yr BP at this region. During the last 4000 yr, the same warm mixed forest was reconstructed below 1700 m and a conifer forest above 1700 m. A great variability of vegetation and climate patterns was recorded for the last 3000 yr particularly at high elevation sites, where warming and cooling trends would be coeval of the Medieval warm period and Little Ice Age, likely related to ENSO variability.  相似文献   

17.
Warming permafrost in European mountains   总被引：3，自引：0，他引：3  
Here we present the first systematic measurements of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient. Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of +1 °C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58-m-deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures. Thus interpretation of the deeper borehole thermal histories must clearly take account of the potential effects of changing snow cover in addition to atmospheric temperatures.  相似文献   

18.
The effect of climate change on carbon in Canadian peatlands   总被引：3，自引：0，他引：3  
Peatlands, which are dominant features of the Canadian landscape, cover approximately 1.136 million km2, or 12% of the land area. Most of the peatlands (97%) occur in the Boreal Wetland Region (64%) and Subarctic Wetland Region (33%). Because of the large area they cover and their high organic carbon content, these peatlands contain approximately 147 Gt soil carbon, which is about 56% of the organic carbon stored in all Canadian soils.A model for estimating peatland sensitivity to climate warming was used to determine both the sensitivity ratings of various peatland areas and the associated organic carbon masses. Calculations show that approximately 60% of the total area of Canadian peatlands and 51% of the organic carbon mass in all Canadian peatlands is expected to be severely to extremely severely affected by climate change.The increase in average annual air temperature of 3–5 °C over land and 5–7 °C over the oceans predicted for northern Canada by the end of this century would result in the degradation of frozen peatlands in the Subarctic and northern Boreal wetland regions and severe drying in the southern Boreal Wetland Region. In addition, flooding of coastal peatlands is expected because of the predicted rise in sea levels. As a result of these changes, a large part of the carbon in the peatlands expected to be severely and extremely severely affected by climate change could be released into the atmosphere as carbon dioxide (CO2) and methane (CH4), which will further increase climate warming.  相似文献   

19.
Considerable debate persists among scientists interested in the nature of the ice cap on the Tibetan Plateau during the late Quaternary. We examine the implications, on this problem, of the high resolution data that has recently become available from the Dunde ice cap in north Tibet. The observed −2% change in the δ18O of the ice formed at the Dunde ice cap during the Last Glacial Stage (LGS) suggests a limit in the range of 5–7°C on the reduction in annual surface air temperature over Tibet during the LGS. This then translates to an Equilibrium Line Altitude (ELA) lowering of 700–1200 m. Due to this lowering, ELA could have reached below the level of the surface of the plateau resulting in an extensive ice sheet formation during LGS.  相似文献   

20.
Rainfed tropical agriculture provides important avenue to ascertain the consequences of climate change. This is because reliability of rainfall accounts for much of the variation in agriculture in the region. In addition, the region is already hot and vulnerable from further warming. This study shows from a climate change experiment using Ricardian method in Cameroon that a 7% decrease in precipitation would cause net revenues from crops to fall US$2.86 billion and a 14% decrease in precipitation would cause net revenue from crops to fall US$3.48 billion. Increases in precipitation would have the opposite effect on net revenues. For a 2.5 °C warming, net revenues would fall by US$0.79 billion, and a 5 °C warming would cause net revenues to fall US$1.94 billion. This highlights that agriculture is not only limited by seasonality and magnitude of moisture availability, but also it is significantly impacted by climate change.  相似文献   

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