Nature2014-06-27 2:11 PM

大气混合作用造成气候模型的不确定性 Spread in model climate sensitivity traced to atmospheric convective mixing

论文摘要 

这篇论文为根据气候模型预测全球变暖中所存在的长期不确定性提供了一个解释。在所预测的气候敏感度(因外部影响而造成的全球变暖程度)对于大气中CO2含量加倍的情形来说范围在1.5° C 至5° C之间。人们一直假设,云模拟所存在的不确定性是造成模型差异的根源。Steven Sherwood等人在这篇论文中分析了43个气候模型的输出,发现气候敏感度的总不确定性中约有一半可以在下对流层和中对流层之间的混合作用的不同处理方式上找到根源,而且这种情况大部分发生在热带。由于受到观测数据的局限,所以本文作者通过模型模拟显示,气候敏感度可能超过3° C,而不是当前所估计的1.5° C这个下限。这样的话,模型所预测的未来变暖会更为严重。

Abstract 

Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

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