Understanding and Attributing Composition-Climate Feedbacks in the Earth System

在过去的130年里，地球表面的温度上升了0.8摄氏度。大量科学证据表明，这种变暖主要是由人类活动造成的：主要是向大气中排放二氧化碳等温室气体。如果温室气体排放继续有增无减，到本世纪末或更早的时候，全球许多地区可能会发生危险的气候变化。因此，至关重要的是，科学界能够提供关于未来几十年气候的定量、可靠信息，使各国政府能够及时实施适当的适应和缓解战略。虽然将温室气体增加与全球变暖联系起来的基础物理学是非常可靠和容易理解的，但地表温度变化的确切幅度取决于一系列复杂的反馈回路，这些反馈回路放大或抑制了响应，就像电子电路一样。例如，北极海冰和冰川的融化是一个增强地表变暖的正反馈，因为地球表面可以吸收更多来自太阳的入射能量，从而导致进一步变暖。如果我们要能够提供有关未来气候的定量信息，就需要全面了解这些反馈。气候预估在很大程度上依赖于复杂的气候“模拟器”，这些“模拟器”捕捉了广泛的物理过程。这些大型计算机程序由世界上最强大的超级计算机运行，在过去的几十年里飞速发展。它们现在包括大气、海洋、海冰、植被、陆地表面、海洋生物地球化学和大气化学过程的复杂表示：即所谓的地球系统模型。这一系列广泛的过程意味着新的相互作用和反馈回路将被捕获，这对我们对气候的理解可能很重要；这些循环中的许多以前可能被忽略了，或者在不太全面的气候模型中没有得到很好的体现，因此需要科学研究来详细了解它们。地球系统中“新”相互作用的一个重要候选者是大气化学过程。化学过程和运输过程对气候条件都很敏感。这意味着大气中其他气体的分布，如臭氧，也将随着二氧化碳水平的增加而改变。臭氧也是一种温室气体，因此其丰度的变化将对我们的气候产生进一步的影响。二氧化碳、臭氧水平和气候之间的这种耦合是化学-气候反馈循环的一个例子。这些反馈很难理解，因为它们涉及到一系列紧密耦合的过程。这项研究的主要目标是调查气候和地球大气组成之间的双向相互作用，并确定哪些反馈回路对我们了解气候变化很重要。由于我们模拟地球系统的能力最近取得了快速进展，这样的研究现在才成为可能。该项目将通过使用英国科学界目前正在建立的最先进的地球系统模型来跟踪这一领域的前沿发展。这项研究将提高我们对化学过程如何影响地球气候的基本理解，并将阐明它们在决定未来几十年气候如何演变方面的作用。

The Earth's surface has warmed by ~0.8 degrees Celsius over the past 130 years. A large body of scientific evidence indicates that the majority of this warming has been driven by mankind's activities: principally the emission of greenhouse gases, like carbon dioxide, into the atmosphere. If greenhouse gas emissions continue unabated, it is considered likely that dangerous climate change will occur in many parts of the globe by the end of the century or earlier. It is therefore crucial that the scientific community is able to provide quantitative, reliable information about climate in the coming decades to enable governments to implement appropriate adaptation and mitigation strategies in good time. Whilst the fundamental physics that links increases in greenhouse gases to global warming is very robust and well understood, the exact magnitude of surface temperature change depends upon a complex array of feedback loops that amplify or damp the response, much like in an electronic circuit. For example, the melting of Arctic sea ice and glaciers is a positive feedback that enhances surface warming because the Earth's surface can absorb more incoming energy from the Sun leading to further warming. A comprehensive understanding of these feedbacks is required if we are to be able to provide quantitative information about future climate.Climate projections are strongly reliant upon complex climate 'simulators' that capture a wide range of physical processes. These large computer programs are run of the world's most powerful supercomputers and have developed in leaps and bounds over the past few decades. They now include sophisticated representations of the atmosphere, ocean, sea ice, vegetation, land surface, ocean biogeochemistry and atmospheric chemical processes: so-called Earth System Models. This wide array of processes means that new interactions and feedback loops will be captured that could be important for our understanding of climate; many of these loops may have been previously ignored or not well represented in less comprehensive climate models and therefore scientific research is required to understand them in detail.An important candidate for 'new' interactions in the Earth system is atmospheric chemical processes. Both chemical and transport processes are sensitive to climatic conditions. This means that the distribution of other gases in the atmosphere, such as ozone, will also change as levels of carbon dioxide increase. Ozone is also a greenhouse gas, so changes in its abundance will have further effects on our climate. This coupling between carbon dioxide, ozone levels and climate is one example of a chemistry-climate feedback loop. These feedbacks are complex to understand because they involve sequences of processes that are intimately coupled. The main goal of this research is to investigate the two-way interactions between climate and the composition of Earth's atmosphere, and to determine which feedback loops are important for our understanding of climate change.Such studies are only now possible because of the recent rapid progress in our capabilities to simulate the Earth system. The project will track the cutting edge developments in this area by using a state-of-the-art Earth System Model currently being built by the UK scientific community. This research will improve our fundamental understanding of how chemical processes affect Earth's climate and will shed light on their role in determining how climate may evolve in the coming decades.