Bala G, Caldeira K, Wickett M, Phillips T J, Lobell D B, Delire C, Mirin A
Energy and Environment Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
Proc Natl Acad Sci U S A. 2007 Apr 17;104(16):6550-5. doi: 10.1073/pnas.0608998104. Epub 2007 Apr 9.
The prevention of deforestation and promotion of afforestation have often been cited as strategies to slow global warming. Deforestation releases CO(2) to the atmosphere, which exerts a warming influence on Earth's climate. However, biophysical effects of deforestation, which include changes in land surface albedo, evapotranspiration, and cloud cover also affect climate. Here we present results from several large-scale deforestation experiments performed with a three-dimensional coupled global carbon-cycle and climate model. These simulations were performed by using a fully three-dimensional model representing physical and biogeochemical interactions among land, atmosphere, and ocean. We find that global-scale deforestation has a net cooling influence on Earth's climate, because the warming carbon-cycle effects of deforestation are overwhelmed by the net cooling associated with changes in albedo and evapotranspiration. Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions. Although these results question the efficacy of mid- and high-latitude afforestation projects for climate mitigation, forests remain environmentally valuable resources for many reasons unrelated to climate.
防止森林砍伐和促进植树造林常常被视为减缓全球变暖的策略。森林砍伐会向大气中释放二氧化碳，这会对地球气候产生变暖影响。然而，森林砍伐的生物物理效应，包括陆地表面反照率、蒸散和云量的变化，也会影响气候。在此，我们展示了使用三维全球碳循环与气候耦合模型进行的多个大规模森林砍伐实验的结果。这些模拟是通过使用一个完全三维的模型进行的，该模型代表了陆地、大气和海洋之间的物理和生物地球化学相互作用。我们发现，全球范围内的森林砍伐对地球气候有净降温影响，因为森林砍伐的变暖碳循环效应被与反照率和蒸散变化相关的净降温所抵消。特定纬度的森林砍伐实验表明，热带地区的植树造林项目在缓解全球变暖方面将明显有益，但如果在高纬度地区实施则会适得其反，而在温带地区只会带来微不足道的好处。尽管这些结果质疑了中高纬度植树造林项目对气候缓解的有效性，但出于与气候无关的许多原因，森林仍然是具有环境价值的资源。
