ADJUST1.5: Defining ADJUSTable (emission) pathways to 1.5 degrees C warming, and assessing their feasibility, physical consequences and impacts.

实现COP21气候协议中1.5摄氏度的升温目标所需的排放途径存在相当大的不确定性。例如，联合国政府间气候变化专门委员会的最新报告表明，1.5摄氏度与累计碳排放量在500至1500亿吨之间是相容的。要将全球变暖控制在1.5摄氏度以内，我们的目标应该是净累计排放量为500GTC还是1500 GTC？我们还不具备所需的气候和碳系统知识来做出决定。事实上，如果要实现1.5摄氏度的变暖目标，就必须有空间来调整我们在21世纪及以后的未来排放计划，以回应我们对气候和碳系统不断发展的了解。该项目将定义和评估1.5摄氏度的可调路径，其中排放路径对21世纪的气候观测做出反应，以最大限度地实现最终变暖目标的可能性。可调节路径将使用来自创新的快速气候模型的数百万个气候模拟进行测试，该模型的整体成员模拟最先进的CMIP5模型的变暖响应范围。我们将评估如何最好地制定升温1.5摄氏度的可调路径，考虑以下因素：(1)最初的减排速度；(2)观测重新评估排放路径之间的时间间隔；(3)因观测重新评估而导致的减排最大变化率；以及(4)无论时间间隔如何，观测触发因素的存在都会导致立即重新评估排放路径。然后，我们将评估将路径调整到1.5摄氏度的可行性如何取决于2100年的瞬时气候排放响应(TCRE)的最终值，以及碳捕获和封存技术的未来潜在演变。我们将评估1.5、2.0和2.4摄氏度变暖对海平面上升和极端海平面事件频率的相对物理后果。我们还将评估海平面上升1.5摄氏度、2.0摄氏度和2.4摄氏度在21世纪和2500年后的影响和成本，重点是脆弱的低洼地区。这个项目能够评估可调路径的独特方面是能够执行数百万次气候模拟，以达到特定的政策驱动的变暖目标。传统的气候模拟使用相同的排放途径，但由于气候响应的不确定性，模拟了广泛的变暖响应。在这里，我们使用了研究团队最近开发的快速气候模型，并模拟了传统模型所显示的气候响应范围。这个快速气候模型可以配置为生成气候模拟，这些模拟都会导致相同的变暖目标，但由于气候响应的不确定性，这些模拟涵盖了广泛的排放途径。

There is considerable uncertainty in the emissions pathway required to achieve the 1.5 degrees C warming target from the COP21 climate agreement. For example, the latest United Nations Intergovernmental Panel on Climate Change report indicated that 1.5 degrees C is compatible with cumulative carbon emissions of somewhere between 500 and 1500 Gigatonnes of carbon. To restrict warming to 1.5 degrees C, should we aim for net cumulative emissions of 500 GtC or of 1500 GtC? We do not yet have the required knowledge of the climate and carbon systems to decide. In fact, if a warming target of 1.5 degrees C is to be achieved, there has to be scope to adjust our future emissions plans over the 21st century and beyond in response to our evolving knowledge of the climate and carbon systems. This project will define and evaluate Adjustable Pathways to 1.5 degrees C, in which the emissions pathway responds to climate observations over the 21st century to maximise the likelihood of delivering the final warming target. The Adjustable Pathways will be tested using millions of climate simulations from an innovative fast climate model whose ensemble members mimic the warming response range of the state-of-the-art CMIP5 models. We will assess how best to formulate the Adjustable Pathway to 1.5 degrees C warming, considering: (1) The initial rate of emissions reductions; (2) The time-interval between observational re-assessment of the emissions pathway; (3) The maximum rate of change of emissions reductions due to observational re-assessment; and (4) The existence of observational triggers that cause immediate re-assessment of the emissions pathway regardless of the time-interval.We will then assess how the feasibility of Adjustable Pathways to 1.5 degrees C depends on the eventual value of the Transient Climate Response to Emission (TCRE) at 2100, and the future potential evolution of carbon capture and storage technology. We will assess the relative physical consequences of 1.5, 2.0 degrees C and 2.4 degrees C warming for sea level rise and the frequency of extreme sea level events. We will also assess impacts and costs of sea level rise 1.5 degrees C, 2.0 degrees C and 2.4 degrees C warming over the 21st century and beyond to year 2500, focusing on vulnerable, low-lying regions.The unique aspect of this project that enables Adjustable Pathways to be evaluated is the ability to perform millions of climate simulations that reach the specific policy-driven warming targets. Conventional climate simulations use identical emissions pathways, but simulate a wide range of warming responses due to the uncertainty in the climate response. Here, we utilise a fast climate model that has recently developed by the research team, and mimics the range of climate responses shown by conventional models. This fast climate model can be configured to generate climate simulations that all lead to the same warming target, but cover a wide range of emissions pathways due to the uncertainty in the climate response.