Garrett Timothy J, Zhao Chuanfeng
Department of Meteorology, University of Utah, Salt Lake City, Utah 84112, USA.
Nature. 2006 Apr 6;440(7085):787-9. doi: 10.1038/nature04636.
There is consensus among climate models that Arctic climate is particularly sensitive to anthropogenic greenhouse gases and that, over the next century, Arctic surface temperatures are projected to rise at a rate about twice the global mean. The response of Arctic surface temperatures to greenhouse gas thermal emission is modified by Northern Hemisphere synoptic meteorology and local radiative processes. Aerosols may play a contributing factor through changes to cloud radiative properties. Here we evaluate a previously suggested contribution of anthropogenic aerosols to cloud emission and surface temperatures in the Arctic. Using four years of ground-based aerosol and radiation measurements obtained near Barrow, Alaska, we show that, where thin water clouds and pollution are coincident, there is an increase in cloud longwave emissivity resulting from elevated haze levels. This results in an estimated surface warming under cloudy skies of between 3.3 and 5.2 W m(-2) or 1 and 1.6 degrees C. Arctic climate is closely tied to cloud longwave emission, but feedback mechanisms in the system are complex and the actual climate response to the described sensitivity remains to be evaluated.
气候模型之间达成的共识是，北极气候对人为温室气体特别敏感，并且在接下来的一个世纪里，北极地表温度预计将以大约全球平均速度两倍的速率上升。北极地表温度对温室气体热排放的响应会受到北半球天气学和当地辐射过程的影响。气溶胶可能通过改变云的辐射特性而成为一个促成因素。在这里，我们评估了之前提出的人为气溶胶对北极云发射和地表温度的贡献。利用在阿拉斯加巴罗附近获得的四年地面气溶胶和辐射测量数据，我们表明，在薄水云与污染同时出现的地方，雾霭水平升高会导致云的长波发射率增加。这导致在多云天空下估计地表变暖幅度在3.3至5.2瓦每平方米（W m(-2)）之间，即1至1.6摄氏度。北极气候与云的长波发射密切相关，但该系统中的反馈机制很复杂，对上述敏感性的实际气候响应仍有待评估。
