Observational constraints on climate projections

这项拟议研究的目标是利用过去一个世纪的气候变化观测结果来改进气候模型对未来气候变化的预测。气候模型是预测未来气候变化的最佳可用工具，为减少温室气体排放和适应未来气候变化的决策提供必要的关键信息。然而，由于气候系统的许多复杂性及其性质的不确定性，气候模型对气候许多方面的未来变化的预测在不同的模型之间存在很大差异。例如，联合国气候变化专门委员会的上一份评估报告得出结论，即使给出21世纪排放的具体轨迹，21世纪全球变暖可能在2.4摄氏度到6.4摄氏度之间。尽管2.4摄氏度的升温对社会和环境的影响可能是可控的，但6.4摄氏度的升温影响可能非常严重。因此，如果气候预测要对政策制定者和整个社会更有用，努力减少这些不确定性是重要的。这项拟议的研究侧重于利用对过去气候变化的观察来改进我们对未来气候变化的预测。目前，世界各地正在进行大量的气候模型模拟，为联合国政府间气候变化专门委员会的下一份报告做准备。通过分析模拟的历史时期(1850-2010年)和未来的气候变化，应该可以确定模拟的过去气候变化和模拟的未来气候变化之间的密切关系。举个简单的例子，我们可能会发现，过去更温暖的模型在未来也往往会更温暖。然后，我们可以使用对过去气候变化的观测，要么排除一些模型对温室气体增加过于敏感，要么不够敏感，或者我们可以重新调整模型预测的比例，以便提高与观测的匹配。到目前为止，此类研究在限制未来预测方面取得的成功有限。但是，具有更好模型的新模拟的可用性，其中许多在2010年完成，为以这种方式改进我们的气候预测提供了一个有希望的新机会。

The objective of the proposed research is to use observations of climate change over the past century to improve climate model predictions of future climate change. Climate models are the best available tools for predicting future climate change, providing key information necessary to inform decisions on reducing greenhouse gas emissions, and adaptation to future climate change. However, due to the many complexities of the climate system and uncertainties in its properties, climate model projections of future change in many aspects of the climate differ strongly between models. For example the last United Nations IPCC assessment report concluded that, even given a specific trajectory of 21st century emissions, 21st century global warming could be anywhere from 2.4°C to 6.4°C. While the impacts on society and the environment from a warming of 2.4°C might be manageable, the impacts of a warming of 6.4°C would likely be very severe. Thus it is important to try to reduce these uncertainties, if climate predictions are to be more useful to policymakers and society at large. The proposed research focuses on using observations of past climate change to improve our predictions of future climate change. A large number of climate model simulations are currently being carried out around the world in preparation for the next report of the UN IPCC report. By analysing simulated climate change over both the historical period (1850-2010) and the future, it should be possible to identify robust relationships between simulated past climate change and simulated future climate change. To take a simple example, we might find that models which warm more in the past tend also to warm more in the future. We can then use observations of past climate change, either to rule out some models as being either too sensitive to greenhouse gas increases or not sensitive enough, or we can rescale model projections so that the match to observations is improved. Such research carried out to date has had limited success in constraining future projections. But the availability of new simulations with better models, many finishing in 2010, presents a promising new opportunity to improve our climate projections in this way.