The impact of performance filtering on climate feedbacks in a perturbed parameter ensemble
The impact of performance filtering on climate feedbacks in a perturbed parameter ensemble
复制标题
性能过滤对扰动参数集合中气候反馈的影响
作者：
J. Rostron;D. Sexton;C. McSweeney;K. Yamazaki;T. Andrews;K. Furtado;M. Ringer;Y. Tsushima
对英国最新一代气候预测（UKCP 18）的一个关键贡献是基于HadGEM 3-GC 3.05的全球耦合模式的扰动参数集合（PPE）。与13个CMIP 5模拟一起，该PPE为用户提供了一个数据集，该数据集对建模不确定性进行了采样，非常适合用于影响研究。对该PPE的全球平均地表温度的评估表明，21世纪的变暖率始终处于CMIP 5范围的高端。在这里，我们调查了一个潜在的贡献因素，这种缺乏传播：从一个更大的，相关的PPE的大气实验中选择合理的成员的方法优先排除了那些预测有更多的负面气候反馈（即较低的气候敏感性）。我们确认情况确实如此。我们表明，在extratrophic长波云强迫的性能发挥了关键作用，通过约束冰云参数，这反过来又限制了反馈分布（虽然因果关系没有建立）。相对较弱的关系驱动这种约束所示，产生较强的长波和短波云反馈分量，这在很大程度上抵消了由于热带高云的变化的关系。此外，我们表明，这些约束的强度是由于结构性的偏差，在outtratroupal长波云强迫整个PPE。我们讨论了如何选择的方法来挑选合理的PPE成员可能会导致一个过于强大的约束时，有一个结构性的偏见和可能的改进，这种方法的未来。
A key contribution to the latest generation of climate projections for the UK (UKCP18) was a perturbed parameter ensemble (PPE) of global coupled models based on HadGEM3-GC3.05. Together with 13 CMIP5 simulations, this PPE provides users with a dataset that samples modelling uncertainty and is ideal for use in impacts studies. Evaluations of global mean surface temperatures for this PPE have shown twenty-first century warming rates consistently at the top end of the CMIP5 range. Here we investigate one potential contributory factor to this lack of spread: that the methodology to select plausible members from a larger, related PPE of atmosphere-only experiments preferentially ruled out those predicted to have more negative climate feedbacks (i.e. lower climate sensitivities). We confirm that this is indeed the case. We show that performance in extratropical long-wave cloud forcing played a key role in this by constraining ice cloud parameters, which in turn constrained the feedback distribution (though causal links are not established). The relatively weak relationship driving this constraint is shown to arise from stronger relationships for the long-wave and short-wave cloud feedback components, which largely cancel out due to changes in tropical high clouds. Moreover, we show that the strength of these constraints is due to a structural bias in extratropical long-wave cloud forcing across the PPE. We discuss how choices made in the methodology to pick the plausible PPE members may result in an overly strong constraint when there is a structural bias and possible improvements to this methodology for the future.
影响因子：
5.1
作者：
Mann, G. W.;Carslaw, K. S.;Johnson, C. E.
通讯作者：
Johnson, C. E.
影响因子：
4.9
作者：
D. Klocke;R. Pincus;J. Quaas
通讯作者：
D. Klocke;R. Pincus;J. Quaas