Observational constraints on climate projections

拟议研究的目的是利用过去一个世纪的气候变化观测来改进气候模式对未来气候变化的预测。气候模式是预测未来气候变化的最佳工具，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，气候模式对未来气候许多方面变化的预估在模式之间存在很大差异。例如，联合国政府间气候变化专门委员会（IPCC）最近的评估报告得出的结论是，即使给出了21世纪排放的具体轨迹，21世纪的全球变暖幅度也可能在2.4°C至6.4°C之间。虽然2.4°C变暖对社会和环境的影响可能是可控的，但6.4°C变暖的影响可能非常严重。因此，如果要使气候预测对政策制定者和整个社会更有用，就必须努力减少这些不确定性。拟议的研究侧重于利用对过去气候变化的观测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式模拟，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。通过分析历史时期（1850-2010）和未来的模拟气候变化，应该有可能确定模拟过去气候变化和模拟未来气候变化之间的可靠关系。举个简单的例子，我们可能会发现过去变暖更多的模式在未来也会变暖更多。然后，我们可以利用对过去气候变化的观测，要么排除一些对温室气体增加过于敏感或不够敏感的模型，要么重新调整模型预测，从而改善与观测结果的匹配。迄今为止进行的这种研究在限制未来预测方面取得的成功有限。但是，使用更好模型的新模拟（许多将在2010年完成）的可用性，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.