气候变化对长江黄河源区生态系统的影响及其水文效应

利用1967年航片数据、1986和2000年两期遥感TM数据,对长江黄河源区高寒生态系统分布格局变化进行了分析,并结合源区气候变化观测数据,分析了源区高寒生态系统变化与气候的关系和陆面生态系统变化对源区水文过程的影响。结果表明：过去40 a来,长江源区高覆盖草甸、高覆盖草原和湿地面积分别减少了13.5%、3.6%和28.9%,黄河源区高覆盖草甸、高覆盖草原和湿地面积分别减少了23.2%、7.0%和13.6%,江河源区低覆盖草甸、草原和沙漠草地面积均不同程度地增加;长江、黄河源区气温变化率分别为0.27和0.31℃/10a,降水的变化趋势在长江、黄河源区分别以0.36和0.07 mm/a的速率递增,气温持续升高和由此引起的冻土退化是导致高寒生态系统退化的主要因素之一;陆面生态系统退化对源区水文过程影响显著,在降水没有明显变化的情况下,长江、黄河源区径流系数分别由1960年代的0.16和0.28下降到21世纪的0.12和0.21,且降水－径流关系减弱,出源径流趋于减少,洪水发生频率显著增加,水源涵养指数持续减小。如何应对气候变化,维护源区高寒生态系统功能,已成为迫切需要关注和解决的关键问题。     

Evaluation and estimation of daily global solar radiation from the estimated direct and diffuse solar radiation

Active layer plays a key role in regulating the dynamics of hydrothermal processes and ecosystems that are sensitive to the changing climate in permafrost regions. However, little is known about the hydrothermal dynamics during freeze-thaw processes in permafrost regions with different vegetation types on the Qinghai-Tibetan Plateau (QTP). In the present study, the freezing and thawing processes at four sites (QT01, 03, 04, and 05) with different vegetation types on the QTP was analyzed. The results indicated that the impact on the soil water and heat during the summer thawing process was markedly greater than that during the autumn freezing process. Furthermore, the thermal-orbit regression slopes for all sites exhibited a homologous variation as the depth increased, with the slowest attenuation for the meadow sites (QT01 and QT03) and a slightly faster attenuation for the desert steppe site (QT05). The air and ground surface temperatures were similar in winter, but the ground surface temperature was significantly higher than the air temperature in summer in the radiation-rich environment at all sites on the QTP. The results also indicated that the n-factors were between 0.36 and 0.55 during the thawing season, and the annual mean temperature near the permafrost table was between − 1.26 and − 1.84 °C. In the alpine desert steppe region, the thermal conditions exhibited to show a warming trend, with a current permafrost table temperature of − 0.22 °C. The annual changing amplitude of the ground temperature at the permafrost table was different for different vegetation types.     

Seasonal variations of net CO2 exchange in European Arctic ecosystems

Summary  The carbon dioxide exchange in arctic and subarctic terrestrial ecosystems has been measured using the eddy-covariance method at sites representing the latitudinal and longitudinal extremes of the European Arctic sea areas as part of the Land Arctic Physical Processes (LAPP) project. The sites include two fen (Kaamanen and Kevo) and one mountain birch ecosystems in subarctic northern Finland (69° N); fen, heathland, and snowbed willow ecosystems in northeastern Greenland (74° N); and a polar semidesert site in Svalbard (79° N). The measurement results, which are given as weekly average diurnal cycles, show the striking seasonal development of the net CO₂ fluxes. The seasonal periods important for the net CO₂ fluxes, i.e. winter, thaw, pre-leaf, summer, and autumn can be identified from measurements of the physical environment, such as temperature, albedo, and greenness. During the late winter period continuous efflux is observed at the permafrost-free Kaamanen site. At the permafrost sites, efflux begins during the thaw period, which lasts about 3–5 weeks, in contrast to the Kaamanen site where efflux continues at the same rate as during the winter. Seasonal efflux maximum is during the pre-leaf period, which lasts about 2–5 weeks. The summer period lasts 6 weeks in NE Greenland but 10–14 weeks in northern Finland. During a high summer week, the mountain birch ecosystem had the highest gross photosynthetic capacity, GP _max, followed by the fen ecosystems. The polar semidesert ecosystem had the lowest GP _max. By the middle of August, noon uptake fluxes start to decrease as the solar elevation angle decreases and senescence begins within the vascular plants. At the end of the autumn period, which lasts 2–5 weeks, topsoil begins to freeze at the end of August in Svalbard; at the end of September at sites in eastern Greenland; and one month later at sites in northern Finland. Received March 1, 2000 Revised October 2, 2000     

Climatic impacts of historical wetland drainage in Switzerland

The effects of historical land-use and land-cover changes on the climate of the Swiss Plateau in the different seasons were investigated. In the 19th century, a civil engineering project was initiated to reshape the lake and river system on the Swiss Plateau in order to ban the frequent flooding during extreme weather events. The landscape modifications consisted primarily of a conversion of wetlands with extended peat soils into a highly productive agricultural landscape. Historical maps (1800–1850) served as a basis for the reconstruction of the past land use. The “Lokal-Modell” of the Consortium for Small-Scale Modelling was used to conduct eight one-month long high-resolution simulations (1.5 × 1.5 km²) with present and past landscape conditions. The modified soil and surface properties led to distinctly altered energy and moisture exchanges at the surface and as a consequence affected the local and regional climate. The climatic changes show different characteristics and magnitudes in the cold (October – March) as compared to the warm season (April – September). The landscape modifications led to an average daytime cooling between −0.12 °C (January) and −0.61 °C (April) and a night-time warming of 0.19 °C−0.34 °C. The differences in the mean monthly temperatures show a warming of 0.1 °C−0.2 °C in the cold season and a cooling of similar magnitude in most of the study area in the warm season. The modification of the radiation budget and the surface energy balance distinctly affected the convective activity in the study area in the warm season, but had only a weak effect on convectivity in the cold season. The cloud coverage in the warm season is therefore distinctly reduced compared to the past.     

Carbon storage in the grasslands of China based on field measurements of above- and below-ground biomass

Above- and below-ground biomass values for 17 types of grassland communities in China as classified by the Chinese Grasslands Resources Survey were obtained from systematic replicated sampling at 78 sites and from published records from 146 sites. Most of the systematic samples were along a 5,000-km-long transect from Hailar, Inner Mongolia (49°15′N, 119°15′E), to Pulan, Tibet (30°15′N, 81°10′E). Above-ground biomass was separated into stem, leaf, flower and fruit, standing dead matter, and litter. Below-ground biomass was measured in 10-cm soil layers to a depth of 30 cm for herbs and to 50 cm for woody plants. Grassland type mean total biomass carbon densities ranged from 2.400 kg m⁻² for swamp to 0.149 kg m⁻² for alpine desert grasslands. Ratios of below- to above-ground carbon density varied widely from 0.99 for tropical tussock grassland to 52.28 for alpine meadow. Most below-ground biomass was in the 0–10 cm soil depth layer and there were large differences between grassland types in the proportions of living and dead matter and stem and leaf. Differences between grassland types in the amount and allocation of biomass showed patterns related to environments, especially aridity gradients. Comparisons of our estimates with other studies indicated that above-ground biomass, particularly forage-yield biomass, is a poor predictor of total vegetation carbon density. Our estimate for total carbon storage in the biomass of the grasslands of China was 3.32 Pg C, with 56.4% contained in the grasslands of the Tibet-Qinghai plateau and 17.9% in the northern temperate grasslands. The need for further standardized and systematic measurements of vegetation biomass to validate global carbon cycles is emphasised.     

The Characteristics of Cold Air Outbreaks over the Eastern Highlands of Kenya

Summary Climatological statistics of extreme temperature events over Kenya are established from the analysis of daily and monthly maximum temperatures for a representative station (Nairobi Dagoretti Corner) over the period 1956–1997. The months of June to August were shown to be the coldest with a mean monthly maximum temperature of less than 22 °C. Seasonal (June to August) mean maximum temperature was 21.5 °C. Using this seasonal mean temperature for the period 1967–1997 delineated 1968 as the coldest year in this series and 1983 as the warmest year. Spectral analysis of the seasonal data, for both the coldest and the warmest years, revealed that the major periods were the quasi-biweekly (10 days) and the Intraseasonal Oscillations (23 days). Secondary peaks occurred at periods of 4–6 and 2.5–3.5 days. A temperature threshold of 16.7 °C during July was used to define cold air outbreaks over Nairobi. This threshold temperature of 16.7 °C was obtained from the mean July maximum temperature (20.9 °C) minus two standard deviations. Notable trends include a decrease in the frequency of station-days, between 1956 and 1997, with temperatures less than 16.7 °C during July. Surface pressure patterns indicate that the origin of the cold air is near latitude 25° S and to the east of mainland South Africa. The cold air near 25° S is advected northwards ahead of the surface pressure ridge. Received July 19, 1999 Revised January 11, 2000     

Spatial and temporal variations in soil temperatures over the Qinghai–Tibet Plateau from 1980 to 2017 based on reanalysis products

A change in soil temperature (ST) is a significant indicator of climate change, so understanding the variations in ST is required for studying the changes of the Qinghai–Tibet Plateau (QTP) permafrost. We investigated the performance of three reanalysis ST products at three soil depths (0–10 cm, 10–40 cm, and 40–100 cm) on the permafrost regions of the QTP: the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim), the second version of the National Centers for Environmental Prediction Climate Forecast System (CFSv2), and the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Our results indicate that all three reanalysis ST products underestimate observations with negative mean bias error values at all three soil layers. The MERRA-2 product performed best in the first and second soil layers, and the ERA-Interim product performed best in the third soil layer. The spatiotemporal changes of annual and seasonal STs on the QTP from 1980 to 2017 were investigated using Sen’s slope estimator and the Mann–Kendall test. There was an increasing trend of ST in the deeper soil layer, which was less than that of the shallow soil layers in the spring and summer as well as annually. In contrast, the first-layer ST warming rate was significantly lower than that of the deeper soil layers in the autumn and winter. The significantly (P < 0.01) increasing trend of the annual ST indicates that the QTP has experienced climate warming during the past 38 years, which is one of the factors promoting permafrost degradation of the QTP.     

Quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from Lake Baikal, Russia

Changes in mean temperature of the coldest (T _c) and warmest month (T _w), annual precipitation (P _ann) and moisture index (α) were reconstructed from a continuous pollen record from Lake Baikal, Russia. The pollen sequence CON01-603-2 (53°57′N, 108°54′E) was recovered from a 386 m water depth in the Continent Ridge and dated to ca. 130–114.8 ky BP. This time interval covers the complete last interglacial (LI), corresponding to MIS 5e. Results of pollen analysis and pollen-based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record. Shrubby tundra covered the area at the beginning of MIS 5e (ca. 130–128 ky), consistent with the end of the Middle Pleistocene glaciation. The late glacial climate was characterised by low winter and summer temperatures (T _c ~ −38 to −35°C and T _w~11–13°C) and low annual precipitation (P _ann~300 mm). However, the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation (reconstructed α~1). Tundra was replaced by boreal conifer forest (taiga) by ca. 128 ky BP, suggesting a transition to the interglacial. Taiga-dominant phase lasted until ca. 117.4 ky BP, e.g. about 10 ky. The most favourable climate conditions occurred during the first half of the LI. P _ann reached 500 mm soon after 128 ky BP. However, temperature changed more gradually. Maximum values of T _c ~ −20°C and T _w~16–17°C are reconstructed from about 126 ky BP. Conditions became gradually colder after ca. 121 ky BP. T _c dropped to ~ −27°C and T _w to ~15°C by 119.5 ky BP. The reconstructed increase in continentality was accompanied by a decrease in P _ann to ~400–420 mm. However, the climate was still humid enough (α~0.9) to support growth of boreal evergreen conifers. A sharp turn towards a dry climate is reconstructed after ca. 118 ky BP, causing retreat of forest and spread of cool grass-shrub communities. Cool steppe dominated the vegetation in the area between ca. 117.5 ky and 114.8 ky BP, suggesting the end of the interglacial and transition to the last glacial (MIS 5d). Shift to the new glaciation was characterised by cool and very dry conditions with T _c ~ −28 to −30°C, T _w~14–15°C, P _ann~250 mm and α~0.5.     

Influence of vegetation changes during the Last Glacial Maximum using the BMRC atmospheric general circulation model

 The influence of different vegetation distributions on the atmospheric circulation during the Last Glacial Maximum (LGM, 21 000 years before present) is investigated. The atmospheric general circulation model of the Bureau of Meteorology Research Center was run using a modern vegetation and in a second experiment with a vegetation reconstruction for the LGM. It is found that a change from conifer to desert and tundra causes an additional LGM cooling of 1–2 °C in Western Europe, up to −4 °C in North America and −6 °C in Siberia. An expansion of dryland vegetation causes an additional annual cooling of 1–2 °C for Australia and northern Africa. On the other hand, an increase of temperature (2 °C) is found in Alaska due to changes in circulation. In the equatorial region the LGM vegetation leads to an increased modelled temperature of 0.5–1.5 °C and decreased precipitation (30%) over land due to a reduction of the tropical rainforest, mainly in Indonesia, where the reduction of precipitation over land is associated with an increase of precipitation of 30% over the western Pacific. Received: 15 December 1999 / Accepted: 10 January 2001     

Spatial-temporal characteristics of temperature variation in China

Summary Spatial-temporal characteristics of temperature variations were analyzed from China daily temperature based on 486 stations during the period 1960–2000. The method of hierarchical cluster analysis was used to divide the territory into sub-regional areas with a coherent evolution, both annually and seasonally. Areas numbering 7–9 are chosen to describe the regional features of air temperature in mainland China. All regions in mainland China experienced increasing trends of annual mean temperature. The trend of increasing temperature was about 0.2–0.3 °C/10 yr in northern China and less than 0.1 °C/10 yr in southern China. In the winter season, the increasing trend of temperature was about 0.5–0.7 °C/10 yr in northern China and about 0.2–0.3 °C/10 yr in southern China. The increasing trend of autumn temperature was mainly located in northwestern China and southwestern China including the Tibetan Plateau. In spring, the rising trend of temperature was concentrated in Northeast China and North China while there was a declining temperature trend of −0.13 °C/10 yr in the upper Yangtze River. In summer, the declining trend of temperature was only concentrated in the mid-low valley of the Yangtze and Yellow Rivers while surrounding this valley there were increasing trends in South China, Southwest China, Northwest China, and Northeast China. Rapid changes in temperature in various regions were detected by the multiple timescale t-test method. The year 1969 was a rapid change point from a high temperature to a low temperature along the Yangtze River and South China. In the years 1977–1979, temperature significantly increased from a lower level to a higher level in many places except for regions in North China and the Yangtze River. Another rapid increasing temperature trend was observed in 1987. In the years 1976–1979, a positive rapid change of summer temperature occurred in northwestern China and southwestern China while a decreasing temperature was found between the Yellow River and the Yangtze River. A rapid increase of winter temperature was found for 1977–1979 and 1985–1986 in many places. There were increasing events of extreme temperature in broad areas except in the north part of Northeast China and the north part of the Xinjiang region. In winter, increasing temperature of the climate state and weakening temperature extremes are observed in northern China. In summer, both increasing temperature of the climate state and enhancing temperature extremes were commonly exhibited in northern China. Present address: Linfen Meteorological Office, Linfen 041000, Shanxi Province, China.     

A multi-model ensemble of downscaled spatial climate change scenarios for the Dommel catchment, Western Europe

Regional or local scale hydrological impact studies require high resolution climate change scenarios which should incorporate some assessment of uncertainties in future climate projections. This paper describes a method used to produce a multi-model ensemble of multivariate weather simulations including spatial–temporal rainfall scenarios and single-site temperature and potential evapotranspiration scenarios for hydrological impact assessment in the Dommel catchment (1,350 km²) in The Netherlands and Belgium. A multi-site stochastic rainfall model combined with a rainfall conditioned weather generator have been used for the first time with the change factor approach to downscale projections of change derived from eight Regional Climate Model (RCM) experiments for the SRES A2 emission scenario for the period 2071–2100. For winter, all downscaled scenarios show an increase in mean daily precipitation (catchment average change of +9% to +40%) and typically an increase in the proportion of wet days, while for summer a decrease in mean daily precipitation (−16% to −57%) and proportion of wet days is projected. The range of projected mean temperature is 7.7°C to 9.1°C for winter and 19.9°C to 23.3°C for summer, relative to means for the control period (1961–1990) of 3.8°C and 16.8°C, respectively. Mean annual potential evapotranspiration is projected to increase by between +17% and +36%. The magnitude and seasonal distribution of changes in the downscaled climate change projections are strongly influenced by the General Circulation Model (GCM) providing boundary conditions for the RCM experiments. Therefore, a multi-model ensemble of climate change scenarios based on different RCMs and GCMs provides more robust estimates of precipitation, temperature and evapotranspiration for hydrological impact assessments, at both regional and local scale.     

Use of an upwelling-diffusion energy balance climate model to simulate and diagnose A/OGCM results

 We demonstrate that a hemispherically averaged upwelling-diffusion energy-balance climate model (UD/EBM) can emulate the surface air temperature change and sea-level rise due to thermal expansion, predicted by the HadCM2 coupled atmosphere-ocean general circulation model, for various scenarios of anthropogenic radiative forcing over 1860–2100. A climate sensitivity of 2.6 °C is assumed, and a representation of the effect of sea-ice retreat on surface air temperature is required. In an extended experiment, with CO₂ concentration held constant at twice the control run value, the HadCM2 effective climate sensitivity is found to increase from about 2.0 °C at the beginning of the integration to 3.85 °C after 900 years. The sea-level rise by this time is almost 1.0 m and the rate of rise fairly steady, implying that the final equilibrium value (the `commitment') is large. The base UD/EBM can fit the 900-year simulation of surface temperature change and thermal expansion provided that the time-dependent climate sensitivity is specified, but the vertical profile of warming in the ocean is not well reproduced. The main discrepancy is the relatively large mid-depth warming in the HadCM2 ocean, that can be emulated by (1) diagnosing depth-dependent diffusivities that increase through time; (2) diagnosing depth-dependent diffusivities for a pure-diffusion (zero upwelling) model; or (3) diagnosing higher depth-dependent diffusivities that are applied to temperature perturbations only. The latter two models can be run to equilibrium, and with a climate sensitivity of 3.85 °C, they give sea-level rise commitments of 1.7 m and 1.3 m, respectively. Received: 27 April 1999 / Accepted: 13 September 2000     

Multi-decadal scenario simulation over Korea using a one-way double-nested regional climate model system. Part 2: future climate projection (2021–2050)

An analysis of simulated future surface climate change over the southern half of Korean Peninsula using a RegCM3-based high-resolution one-way double-nested system is presented. Changes in mean climate as well as the frequency and intensity of extreme climate events are discussed for the 30-year-period of 2021–2050 with respect to the reference period of 1971–2000 based on the IPCC SRES B2 emission scenario. Warming in the range of 1–4°C is found throughout the analysis region and in all seasons. The warming is maximum in the higher latitudes of the South Korean Peninsula and in the cold season. A large reduction in snow depth is projected in response to the increase of winter minimum temperature induced by the greenhouse warming. The change in precipitation shows a distinct seasonal variation and a substantial regional variability. In particular, we find a large increase of wintertime precipitation over Korea, especially in the upslope side of major mountain systems. Summer precipitation increases over the northern part of South Korea and decreases over the southern regions, indicating regional diversity. The precipitation change also shows marked intraseasonal variations throughout the monsoon season. The temperature change shows a positive trend throughout 2021–2050 while the precipitation change is characterized by pronounced interdecadal variations. The PDF of the daily temperature is shifted towards higher values and is somewhat narrower in the scenario run than the reference one. The number of frost days decreases markedly and the number of hot days increases. The regional distribution of heavy precipitation (over 80 mm/day) changes considerably, indicating changes in flood vulnerable regions. The climate change signal shows pronounced fine scale signal over Korea, indicating the need of high-resolution climate simulations     

A permafrost warming in a cooling Antarctica?

The magnitude and even direction of recent Antarctic climate change is still debated because the paucity of long and complete instrumental data records. While along Antarctic Peninsula a strong warming coupled with large retreat of glaciers occurred, in continental Antarctica a cooling was recently detected. Here, the first existing permafrost data set longer than 10 years recorded in continental Antarctica is presented. Since 1997 summer ground surface temperature showed a strong warming trend (0.31°C per year) although the air temperature was almost stable. The summer ground surface temperature increase seemed to be influenced mainly by the increase of the total summer radiation as confirmed also by the increase of the summer thawing degree days. In the same period the active layer exhibited a thickening trend (1 cm per year) comparable with the thickening rates observed in several Arctic locations where air warming occurred. At all the investigated depths permafrost exhibited an increase of mean annual temperature of approximately 0.1°C per year. The dichotomy between active layer thickness and air temperature trends can produce large unexepected and unmodelled impacts on ecosystems and CO₂ balance.     

Sensitivity of European glaciers to precipitation and temperature – two case studies

A nonlinear backpropagation network (BPN) has been trained with high-resolution multiproxy reconstructions of temperature and precipitation (input data) and glacier length variations of the Alpine Lower Grindelwald Glacier, Switzerland (output data). The model was then forced with two regional climate scenarios of temperature and precipitation derived from a probabilistic approach: The first scenario (“no change”) assumes no changes in temperature and precipitation for the 2000–2050 period compared to the 1970–2000 mean. In the second scenario (“combined forcing”) linear warming rates of 0.036–0.054°C per year and changing precipitation rates between −17% and +8% compared to the 1970–2000 mean have been used for the 2000–2050 period. In the first case the Lower Grindelwald Glacier shows a continuous retreat until the 2020s when it reaches an equilibrium followed by a minor advance. For the second scenario a strong and continuous retreat of approximately −30 m/year since the 1990s has been modelled. By processing the used climate parameters with a sensitivity analysis based on neural networks we investigate the relative importance of different climate configurations for the Lower Grindelwald Glacier during four well-documented historical advance (1590–1610, 1690–1720, 1760–1780, 1810–1820) and retreat periods (1640–1665, 1780–1810, 1860–1880, 1945–1970). It is shown that different combinations of seasonal temperature and precipitation have led to glacier variations. In a similar manner, we establish the significance of precipitation and temperature for the well-known early eighteenth century advance and the twentieth century retreat of Nigardsbreen, a glacier in western Norway. We show that the maritime Nigardsbreen Glacier is more influenced by winter and/or spring precipitation than the Lower Grindelwald Glacier.     

Winter climate change in alpine tundra: plant responses to changes in snow depth and snowmelt timing

Snow is an important environmental factor in alpine ecosystems, which influences plant phenology, growth and species composition in various ways. With current climate warming, the snow-to-rain ratio is decreasing, and the timing of snowmelt advancing. In a 2-year field experiment above treeline in the Swiss Alps, we investigated how a substantial decrease in snow depth and an earlier snowmelt affect plant phenology, growth, and reproduction of the four most abundant dwarf-shrub species in an alpine tundra community. By advancing the timing when plants started their growing season and thus lost their winter frost hardiness, earlier snowmelt also changed the number of low-temperature events they experienced while frost sensitive. This seemed to outweigh the positive effects of a longer growing season and hence, aboveground growth was reduced after advanced snowmelt in three of the four species studied. Only Loiseleuria procumbens, a specialist of wind exposed sites with little snow, benefited from an advanced snowmelt. We conclude that changes in the snow cover can have a wide range of species-specific effects on alpine tundra plants. Thus, changes in winter climate and snow cover characteristics should be taken into account when predicting climate change effects on alpine ecosystems.     

Increasing impacts of climate change upon ecosystems with increasing global mean temperature rise

In a meta-analysis we integrate peer-reviewed studies that provide quantified estimates of future projected ecosystem changes related to quantified projected local or global climate changes. In an advance on previous analyses, we reference all studies to a common pre-industrial base-line for temperature, employing up-scaling techniques where necessary, detailing how impacts have been projected on every continent, in the oceans, and for the globe, for a wide range of ecosystem types and taxa. Dramatic and substantive projected increases of climate change impacts upon ecosystems are revealed with increasing annual global mean temperature rise above the pre-industrial mean (ΔT_g). Substantial negative impacts are commonly projected as ΔT_g reaches and exceeds 2°C, especially in biodiversity hotspots. Compliance with the ultimate objective of the United Nations Framework Convention on Climate Change (Article 2) requires that greenhouse gas concentrations be stabilized within a time frame “sufficient to allow ecosystems to adapt naturally to climate change”. Unless ΔT_g is constrained to below 2°C at most, results here imply that it will be difficult to achieve compliance. This underscores the need to limit greenhouse gas emissions by accelerating mitigation efforts and by protecting existing ecosystems from greenhouse-gas producing land use change processes such as deforestation.     

Climate change impact on snow and soil temperature in boreal Scots pine stands

Scenarios indicate that the air temperature will increase in high latitude regions in coming decades, causing the snow covered period to shorten, the growing season to lengthen and soil temperatures to change during the winter, spring and early summer. To evaluate how a warmer climate is likely to alter the snow cover and soil temperature in Scots pine stands of varying ages in northern Sweden, climate scenarios from the Swedish regional climate modelling programme SWECLIM were used to drive a Soil-Vegetation-Atmosphere Transfer (SVAT)-model (COUP). Using the two CO₂ emission scenarios A and B in the Hadley centres global climate model, HadleyA and HadleyB, SWECLIM predicts that the annual mean air temperature and precipitation will increase at most 4.8°C and 315 mm, respectively, within a century in the study region. The results of this analysis indicate that a warmer climate will shorten the period of persistent snow pack by 73–93 days, increase the average soil temperature by 0.9–1.5°C at 10 cm depth, advance soil warming by 15–19 days in spring and cause more soil freeze–thaw cycles by 31–38%. The results also predict that the large current variations in snow cover due to variations in tree interception and topography will be enhanced in the coming century, resulting in increased spatial variability in soil temperatures.     

Effects of observed and experimental climate change on terrestrial ecosystems in northern Canada: results from the Canadian IPY program

Tundra and taiga ecosystems comprise nearly 40?% of the terrestrial landscapes of Canada. These permafrost ecosystems have supported humans for more than 4500?years, and are currently home to ca. 115,000 people, the majority of whom are First Nations, Inuit and Métis. The responses of these ecosystems to the regional warming over the past 30?C50?years were the focus of four Canadian IPY projects. Northern residents and researchers reported changes in climate and weather patterns and noted shifts in vegetation and other environmental variables. In forest-tundra areas tree growth and reproductive effort correlated with temperature, but seedling establishment was often hindered by other factors resulting in site-specific responses. Increased shrub cover has occurred in sites across the Arctic at the plot and landscape scale, and this was supported by results from experimental warming. Experimental warming increased vegetation cover and nutrient availability in most tundra soils; however, resistance to warming was also found. Soil microbial diversity in tundra was no different than in other biomes, although there were shifts in mycorrhizal diversity in warming experiments. All sites measured were sinks for carbon during the growing season, with expected seasonal and latitudinal patterns. Modeled responses of a mesic tundra system to climate change showed that the sink status will likely continue for the next 50?C100?years, after which these tundra systems will likely become a net source of carbon dioxide to the atmosphere. These IPY studies were the first comprehensive assessment of the state and change in Canadian northern terrestrial ecosystems and showed that the inherent variability in these systems is reflected in their site-specific responses to changes in climate. They also showed the importance of using local traditional knowledge and science, and provided extensive data sets, sites and researchers needed to study and manage the inevitable changes in the Canadian North.     

A probabilistic calibration of climate sensitivity and terrestrial carbon change in GENIE-1

In order to investigate Last Glacial Maximum and future climate, we “precalibrate” the intermediate complexity model GENIE-1 by applying a rejection sampling approach to deterministic emulations of the model. We develop ~1,000 parameter sets which reproduce the main features of modern climate, but not precise observations. This allows a wide range of large-scale feedback response strengths which generally encompass the range of GCM behaviour. We build a deterministic emulator of climate sensitivity and quantify the contributions of atmospheric (±0.93°C, 1σ) vegetation (±0.32°C), ocean (±0.24°C) and sea–ice (±0.14°C) parameterisations to the total uncertainty. We then perform an LGM-constrained Bayesian calibration, incorporating data-driven priors and formally accounting for structural error. We estimate climate sensitivity as likely (66% confidence) to lie in the range 2.6–4.4°C, with a peak probability at 3.6°C. We estimate LGM cooling likely to lie in the range 5.3–7.5°C, with a peak probability at 6.2°C. In addition to estimates of global temperature change, we apply our ensembles to derive LGM and 2xCO₂ probability distributions for land carbon storage, Atlantic overturning and sea–ice coverage. Notably, under 2xCO₂ we calculate a probability of 37% that equilibrium terrestrial carbon storage is reduced from modern values, so the land sink has become a net source of atmospheric CO₂.