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

实现COP 21气候协议规定的1.5摄氏度升温目标所需的排放途径存在相当大的不确定性。例如，最新的联合国政府间气候变化专门委员会报告指出，1.5摄氏度与500至1500千兆吨碳的累积碳排放量是相容的。为了将变暖限制在1.5摄氏度，我们应该将净累积排放量定为500 GtC还是1500 GtC？我们还没有必要的气候和碳系统的知识来决定。事实上，如果要实现1.5摄氏度的升温目标，就必须有空间调整我们在21世纪及以后的未来排放计划，以应对我们对气候和碳系统不断发展的认识。该项目将定义和评估1.5摄氏度的可调节路径，其中排放路径响应21世纪世纪的气候观测，以最大限度地提高实现最终变暖目标的可能性。可调节路径将使用来自创新快速气候模型的数百万次气候模拟进行测试，该模型的集合成员模拟了最先进的CMIP 5模型的变暖响应范围。我们将评估如何最好地制定应对1.5摄氏度变暖的可调整路径，考虑：（1）初始减排率;（2）观测重新评估排放路径之间的时间间隔;（3）由于观测重新评估导致的减排量变化的最大速率;以及（4）存在观测触发因素，导致立即重新评估排放路径，无论时间-然后，我们将评估可调节路径到1.5摄氏度的可行性如何取决于2100年瞬态气候对排放的响应（TCRE）的最终值，以及碳捕获和储存技术的未来潜在发展。我们将评估1.5、2.0和2.4摄氏度升温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21世纪及以后至2500年海平面上升1.5摄氏度、2.0摄氏度和2.4摄氏度变暖的影响和成本，重点关注脆弱的低洼地区。该项目的独特之处在于，能够对可调节路径进行评估的能力是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路径，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，我们利用了研究团队最近开发的快速气候模型，并模拟了传统模型显示的气候响应范围。这种快速气候模型可以配置为生成气候模拟，这些模拟都导致相同的变暖目标，但由于气候响应的不确定性，覆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.