Department of Physics, University of Oxford, Oxford OX1 3PU, UK.
Nature. 2011 Feb 17;470(7334):382-5. doi: 10.1038/nature09762.
Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing. Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 1766, these floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at £1.3 billion (refs 5, 6). Although the flooding was deemed a 'wake-up call' to the impacts of climate change at the time, such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming, but fail to account fully for the complex hydrometeorology associated with flooding. Here we present a multi-step, physically based 'probabilistic event attribution' framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000. Using publicly volunteered distributed computing, we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather, both under realistic conditions, and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred. Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.
人们对将破坏性天气相关事件的风险归因于人为气候变化的兴趣日益增加。然而，用于研究归因问题的气候模型通常无法解决与破坏性事件相关的天气系统，例如 2000 年 10 月和 11 月的英国洪水。这场洪水发生在英格兰和威尔士自 1766 年有记录以来最潮湿的秋季，洪水破坏了该地区近 10000 处房产，严重扰乱了服务，并造成估计 13 亿英镑的保险损失（参考文献 5、6）。尽管当时这场洪水被认为是气候变化影响的“警钟”，但此类说法通常仅得到增加全球变暖下极端降水的一般热力学论点的支持，但未能充分考虑与洪水相关的复杂水文气象学。在这里，我们提出了一个多步骤、基于物理的“概率事件归因”框架，表明全球人为温室气体排放极有可能大大增加了 2000 年秋季英格兰和威尔士发生洪水的风险。我们利用公开自愿的分布式计算，生成了数千次 2000 年秋季天气的季节预测分辨率气候模型模拟，既有现实条件下的模拟，也有假设这些温室气体排放和由此产生的大规模变暖从未发生过的条件下的模拟。结果被输入到一个降水-径流模型中，该模型用于模拟英格兰和威尔士的严重日径流事件（洪水事件的代理指标）。人为因素的精确贡献仍然不确定，但在十分之九的情况下，我们的模型结果表明，20 世纪人为温室气体排放增加了 2000 年秋季英格兰和威尔士发生洪水的风险，超过 20%，在三分之二的情况下增加了超过 90%。
