荒漠化与气候变化间反馈机制研究进展

Progress in feedback mechanism between desertification and climate change

荒漠化和气候变化是全球关注的重大环境问题 ,两者间的反馈机制是目前科学研究的热点之一。从荒漠化与气候变化间的反馈机制和荒漠化及其防治对碳源 /汇的影响两方面对其研究进展进行了评述。以往的研究表明 ,荒漠化对区域乃至全球气候变化的影响主要通过荒漠化过程中植被覆盖降低 -地表反射率提高和 (或 )土壤含水量降低 -降雨量降低 -植被覆盖降低这样一个正反馈机制 (荒漠化生物地球物理模型“Charney假说”及其衍生理论 )来实现的 ,此外大气中悬浮的沙尘具有明显抑制降雨的作用 ,土地荒漠化所导致的沙尘暴频发及其影响范围之大也将对全球气候变化产生显著影响。气候变化对荒漠化的影响则表现在对荒漠化的范围、发展速度和强度以及潜在危险性及干旱生态系统的结构、功能及生产力的影响上。同时作为全球重要的碳贮存地 ,干旱区的变化从一定程度上影响到大气中 CO2 的收支 ,据估算全球荒漠化所导致的碳损失总量为 18～ 2 8Pg C,其中中国近 4 0 a来因土地沙质荒漠化导致的 CO2 净释放量为 91Mt C,如果 UNEP建议的退化土地治理措施得以实施 ,每年可固定 37Pg的碳 ,约占 CO2 年排放量的 15 % ,其投入低于一些限制 CO2 排放的措施 ,因此具有很大的吸引力。从目前的研究进展来看 ,大多数研究尚处于定性描述?

Desertification and climate change are two of globally environmental issues, and feedback mechanism between them is becoming one of research forefronts. In this paper, we review research progress on this topic from feedback between desertification and climate change and effects of desertification and its control on carbon source/sink. The existing results show that on the one hand, the effects of desertification on regional and global climate change result mainly from a positive feedback loop as vegetation cover decreasing-albedo increasing and (or) soil moisture decreasing-precipitation decreasing-vegetation cover decreasing (Charney's hypothesis and its derivative theories), and that sand dusts suspending in atmosphere can suppress precipitation, and high-frequent dust storms and their large cover scope will also overlap their effects on global climate change; on the other hand, climate change influences on extent, rate, intensity and potential risk of desertification, and on structure, function and productivity in dryland ecosystem. In meanwhile, as globally important carbon store, dryland change will affect budget of carbon in atmosphere to the extent, it is estimated that total carbon loss from desertification is 18～28 Pg C globally,and net CO_2 amount released from desertified sandy lands of china is about 91Mt C,if all the land restoration measures suggested by UNEP were adopted, the net effect on carbon sequestration would be over 37 Pg per year, accounting for 15 percent of atmospheric CO_2 emissions, and the input is actually considerably lower than the cost of some carbon source limitation measures and seems very attractive. From aspects of current research progress, despite of building of regionally numerical model, the majority of results is gotten by extrapolation or estimation, hence future emphases should be put on the development of new numerical models and scale-up of them, including (a) to quantify the impacts of climate change on resilience, biodiversity, productivity and health of dryland ecosystem, (b) to model the impacts of desertification on regional and global climate change, and (c) to evaluate the influence of desertification combating, particularly some large-scale ecological projects such as Three North Protection Forest Project, on climate change. In conclusion, it is very important to better understand the feedback mechanism between desertification and climate change from science and policy views, which not only is helpful in implementing global or regional desertification control, but provide scientific base for negotiation of UN Convention to climate change.