Department of Earth & Planetary Science, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2010 Jan 26;107(4):1295-300. doi: 10.1073/pnas.0913846107. Epub 2010 Jan 7.
Arctic climate is projected to change dramatically in the next 100 years and increases in temperature will likely lead to changes in the distribution and makeup of the Arctic biosphere. A largely deciduous ecosystem has been suggested as a possible landscape for future Arctic vegetation and is seen in paleo-records of warm times in the past. Here we use a global climate model with an interactive terrestrial biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is up to 1.5 times larger than the forcing due to albedo change from the forest. Furthermore, the greenhouse warming by additional water vapor melts sea-ice and triggers a positive feedback through changes in ocean albedo and evaporation. Land surface albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration of water vapor and feedbacks from the ocean and sea-ice.
北极气候预计在未来 100 年内将发生剧烈变化，气温上升可能导致北极生物圈的分布和组成发生变化。落叶林生态系统被认为是未来北极植被的一种可能景观，在过去温暖时期的古记录中也有体现。在这里，我们使用具有交互陆地生物圈的全球气候模型来研究在高北纬地区增加落叶树对裸地的影响。我们发现，增强蒸腾作用（与森林覆盖面积扩大有关）引起的大气顶部辐射不平衡，比森林反照率变化引起的强迫作用大 1.5 倍。此外，额外水蒸气的温室增暖融化海冰，并通过海洋反照率和蒸发的变化引发正反馈。陆地表面反照率的变化被认为是树木在高纬度地区直接改变气候的主要机制，但我们的研究结果表明，通过水蒸气的蒸腾和海洋及海冰的反馈，存在另一种机制。
