Harding Richard, Kuhry Peter, Christensen Torben R, Sykes Martin T, Dankers Rutger, van der Linden Sandra
Land/Atmosphere Interaction Section, Centre for Ecology and Hydrology at Wallingford, England.
Ambio. 2002 Aug;Spec No 12:47-55.
Feedbacks, or internal interactions, play a crucial role in the climate system. Negative feedback will reduce the impact of an external perturbation, a positive feedback will amplify the effect and could lead to an unstable system. Many of the feedbacks found in the climate system are positive; thus, for example, increasing CO2 levels will increase temperature, reduce the snow cover, increase the absorption of radiation and hence increase temperature further. The most obvious feedbacks, such as the snow example quoted above, are already included within our models of the climate and earth system. Others, such as the impact of increasing forest cover due to global warming, are only just being included. Others, such as, the impact of global warming on the northern peatlands and the impact of freshwater flows on the Arctic Ocean are not yet considered. The contrast in surface characteristics between low tundra vegetation to high taiga forest is considerable. The contrast is greatest in the winter, when the tundra is snow covered but the trees of the taiga protrude through the snow pack, and is probably the greatest contrast found on the land surface anywhere. This variation causes massive changes in the energy fluxes at the surface and hence the temperature conditions on the ground and within the atmosphere. There will be large resultant changes in the vegetation development, the carbon fluxes, the permafrost and the hydrology. The Arctic is already experiencing change and it is essential for us to understand the basic processes, and how these interact, to be confident of our predictions of environmental change in the future.
反馈，即内部相互作用，在气候系统中起着至关重要的作用。负反馈会减少外部扰动的影响，正反馈则会放大这种影响并可能导致系统不稳定。气候系统中发现的许多反馈都是正反馈；例如，二氧化碳水平升高会导致温度上升，减少积雪覆盖，增加辐射吸收，进而进一步升高温度。最明显的反馈，如上述的积雪例子，已经包含在我们的气候和地球系统模型中。其他一些反馈，如全球变暖导致森林覆盖增加的影响，才刚刚被纳入考虑。还有一些反馈，如全球变暖对北方泥炭地的影响以及淡水流动对北冰洋的影响，尚未得到考虑。从低苔原植被到高泰加林的地表特征差异相当大。这种差异在冬季最为显著，此时苔原被积雪覆盖，而泰加林的树木则从雪层中穿出，这可能是陆地上任何地方最大的地表差异。这种变化会导致地表能量通量发生巨大变化，进而影响地面和大气中的温度状况。植被发育、碳通量、永久冻土和水文状况也将随之发生重大变化。北极已经在经历变化，对我们来说，了解基本过程以及它们如何相互作用，对于我们未来对环境变化的预测充满信心至关重要。
