Modelling the climate response to greenhouse gas emissions: characteristics and policy implications

在过去十年中，气候建模的一个重大进展是将碳循环纳入模型。这些"地球系统"或"气候-碳循环耦合模型"代表了从二氧化碳（CO2）排放到气候变化的整个因果链，同时考虑到气候与碳循环之间的相互作用。最近对这些模型的研究表明，即使在任何时候停止排放，由人类造成的二氧化碳排放造成的气候变化也可能持续许多世纪。此外，这些研究表明，未来全球变暖的量取决于释放到大气中的CO2的累积量。这些发现的一个含义是，气候目标，如广泛倡导的2 C目标，可以用累积的碳排放量来表示。本提案的目的是通过探索以下问题来扩展这些早期研究：（1）其他气候变量（如降水量）的变化是否像温度变化一样持久？持久性水平是否取决于排放到大气中的二氧化碳总量？(2)需要减少哪些排放才能从“危险”的变暖水平恢复过来？如果从危险的变暖中恢复需要负排放，即从大气中净去除二氧化碳（"空气捕获"），这些排放在技术上是否可行？(3)哪些累积排放量符合其他气候目标，例如与海洋酸化或海平面上升有关的目标？这些排放量与符合2C目标的排放量相比如何？(4)与甲烷等其他温室气体有关的气候变化有多持久？这些气体在减缓气候变化方面的潜在作用是什么？该研究项目取得的成果将加深我们对地球气候如何应对人为温室气体排放的理解，并将为制定有效的气候政策提供有用的见解。

A major advance in climate modelling over the last decade has been the incorporation of the carbon cycle into models. These "Earth system" or "coupled climate-carbon cycle models" represent the entire causal chain from carbon dioxide (CO2) emissions to climate change, taking into account the interactions between climate and the carbon cycle. Recent studies with these models have shown that climate change caused by human-caused CO2 emissions may persist for many centuries even if emissions were to be halted at any point in time. Further, such studies have shown that the amount of future global warming is determined by the accumulated amount of CO2 released into the atmosphere. One implication of these findings is that climate targets, such as the widely advocated 2 C target, can be expressed in terms of accumulated carbon emissions.The purpose of this proposal is to expand on these early studies by exploring the following questions:(1) Are changes in other climate variables (e.g. precipitation) as persistent as temperature changes? Does the level of persistence depend on the total amount of CO2 released into the atmosphere?(2) What emissions cuts are needed to revert from "dangerous" levels of warming? If reverting from dangerous warming requires negative emissions, i.e. net removal of CO2 from the atmosphere ("air capture"), are these emissions technologically feasible?(3) What are the cumulative emissions compatible with other climate targets, e.g. related to ocean acidification or sea level rise? How do these emissions compare to those compatible with the 2 C target?(4) How persistent are the climate changes associated with other greenhouse gases, e.g. methane? What is the potential role of these gases in climate change mitigation?The results achieved under this research program will deepen our understanding of how the Earth's climate responds to human-caused greenhouse gas emissions, and will provide useful insights for developing effective climate policy.