Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA.
Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
Science. 2016 Apr 8;352(6282):224-7. doi: 10.1126/science.aad5300.
Global climate model (GCM) estimates of the equilibrium global mean surface temperature response to a doubling of atmospheric CO2, measured by the equilibrium climate sensitivity (ECS), range from 2.0° to 4.6°C. Clouds are among the leading causes of this uncertainty. Here we show that the ECS can be up to 1.3°C higher in simulations where mixed-phase clouds consisting of ice crystals and supercooled liquid droplets are constrained by global satellite observations. The higher ECS estimates are directly linked to a weakened cloud-phase feedback arising from a decreased cloud glaciation rate in a warmer climate. We point out the need for realistic representations of the supercooled liquid fraction in mixed-phase clouds in GCMs, given the sensitivity of the ECS to the cloud-phase feedback.
全球气候模式（GCM）对大气 CO2 倍增引起的全球平均地表温度平衡响应的估计值，即平衡气候敏感性（ECS），范围在 2.0°C 到 4.6°C 之间。云是造成这种不确定性的主要原因之一。在这里，我们表明，在混合相云（由冰晶和过冷液滴组成）受到全球卫星观测约束的模拟中，ECS 可以高达 1.3°C。更高的 ECS 估计值与云相反馈的减弱直接相关，这是由于在更温暖的气候中云冰化率降低所致。鉴于 ECS 对云相反馈的敏感性，我们指出在 GCM 中需要对混合相云中过冷液体部分进行真实的表示。
