政府间气候变化专门委员会（IPCC）第六次评估报告（AR6）第一工作组报告对多年冻土区土壤碳储量、碳汇效应及未来气候情景下温室气体排放进行了归纳和总结。报告明确指出，北半球多年冻土区表层土壤和深层沉积物的有机碳储量为1 460～1 600 PgC（1 Pg=10亿吨）(中等信度)。随着气候持续变暖，多年冻土显著退化，土壤有机质迅速分解并以二氧化碳（CO2）或甲烷（CH4）的形式释放到大气中，加速了气候变暖。在未来全球变暖情景下，近地表多年冻土面积将显著减少，并向大气释放CO2和CH4，造成多年冻土碳与气候的正反馈作用。报告还指出，预计到2100年，气温每升高1℃，多年冻土区CO2和CH4的排放量分别相当于18（3.1～41） PgC和2.8（0.7～7.3） PgC（低信度）。但由于所使用的估算数据异质性较大及模型之间的一致性有限，并且对多年冻土环境驱动因素及过程模型的认知尚不完整，故多年冻土对气候变化反馈的时间及幅度的可信度还处于较低水平。

政府间气候变化专门委员会（IPCC）第六次评估报告（AR6）第一工作组报告《气候变化2021：自然科学基础》对全球多年冻土变化的观测事实、气候模式中的评估与未来预测以及多年冻土变化的影响等进行了系统归纳和总结。报告指出，在过去30～40年，多年冻土30 m以上的温度普遍升高（高信度）。2007—2016年期间，全球多年冻土温度升高了（0.29±0.12）℃（中等信度），与不连续多年冻土区的冻土变暖[（0.20±0.10）℃]相比，连续多年冻土区观测到了更强的变暖[（0.39±0.15）℃]。活动层厚度在整个泛北极地区都普遍增加（中等信度）。随着全球气候变暖，多年冻土的范围和体积将会缩小（高信度）。全球地表气温每升高1°C，距地表3 m的多年冻土体积将减少约25%（中等信度）。然而，由于地球系统模型中对与多年冻土相关物理过程的表征不完整，多年冻土的体积缩小可能被低估。报告还指出，多年冻土退化对全球冻土-碳气候反馈、生态系统及基础设施等方面造成了显著影响，在气候模式及风险评估中应予以考虑。

This study estimates direct radiative forcing by tropospheric ozone and all aerosols between the years 1850 and 2000, using the new IPCC AR5 (the Intergovernmental Panel on Climate Change Fifth Assessment Report) emissions inventories and a fully coupled chemistry-aerosol general circulation model. As compared to the previous Global Emissions Inventory Activity (GEIA) data, that have been commonly used for forcing estimates since 1990, the IPCC AR5 emissions inventories report lower anthropogenic emissions of organic carbon and black carbon aerosols and higher sulfur and NOx emissions. The simulated global and annual mean burdens of sulfate, nitrate, black carbon (BC), primary organic aerosol (POA), secondary organic aerosol (SOA), and ozone were 0.79, 0.35, 0.05, 0.49, 0.34, and 269 Tg, respectively, in the year 1850, and 1.90, 0.90, 0.11, 0.71, 0.32, and 377 Tg, respectively, in the year 2000. The estimated annual mean top of the atmosphere (TOA) direct radiative forcing of all anthropogenic aerosols based on the AR5 emissions inventories is -0.60 W m(-2) on a global mean basis from 1850 to 2000. However, this is -2.40 W m(-2) when forcing values are averaged over eastern China (18-45 degrees N and 95-125 degrees E). The value for tropospheric ozone is 0.17 W m(-2) on a global mean basis and 0.24 W m(-2) over eastern China. Forcing values indicate that the climatic effect of aerosols over eastern China is much more significant than the globally averaged effect.

A spatially distributed, physically based, hydrologic modeling system (MIKE SHE) was applied to quantify intra- and inter-annual discharge from the snow and glacierized Zackenberg River drainage basin (512 km 2; 20% glacier cover) in northeast Greenland. Evolution of snow accumulation, distribution by wind-blown snow, blowing-snow sublimation, and snow and ice surface melt were simulated by a spatially distributed, physically based, snow-evolution modelling system (SnowModel) and used as input to MIKE SHE. Discharge simulations were performed for three periods 1997-2001 (calibration period), 2001-2005 (validation period), and 2071-2100 (scenario period). The combination of SnowModel and MIKE SHE shows promising results; the timing and magnitude of simulated discharge were generally in accordance with observations (R-2 = 0.58); however, discrepancies between simulated and observed discharge hydrographs do occur (maximum daily difference up to 44.6 m(3) s(-1) and up to 9% difference between observed and simulated cumulative discharge). The model does not perform well when a sudden outburst of glacial dammed water occurs, like the 2005 extreme flood event. The modelling study showed that soil processes related to yearly change in active layer depth and glacial processes (such as changes in yearly glacier area, seasonal changes in the internal glacier drainage system, and the sudden release of glacial bulk water storage) need to be determined, for example, from field studies and incorporated in the models before basin runoff can be quantified more precisely. The SnowModel and MIKE SHE model only include first-order effects of climate change. For the period 2071-2100, future IPCC A2 and B2 climate scenarios based on the HIRHAM regional climate model and HadCM3 atmosphere-ocean general circulation model simulations indicated a mean annual Zackenberg runoff about 1.5 orders of magnitude greater (around 650 mmWE year(-1)) than from today 1997-2005 (around 430 mmWE year(-1)), mainly based on changes in negative glacier net mass balance. Copyright (c) 2007 John Wiley & Sons, Ltd.