Allocating Responsibility for Regional, Glacier-Related Sea-Level Change

冰川融化是全球平均海平面上升的三个主要原因之一，另外两个是海水的热膨胀以及格陵兰岛和南极冰盖的质量损失。在整个20世纪，它们更有可能是海平面上升的主要原因。在未来的几个世纪里，预计格陵兰岛和南极洲的质量损失率将显著增加，而冰川的贡献则因其相对较小而受到限制。然而，在21世纪，冰川的贡献仍将是巨大的，至少在未来300年里，冰川的贡献是不可忽视的。在20世纪下半叶，可以清楚地发现人为因素对冰川质量损失的贡献，近几十年来，人为因素已成为冰川质量损失的主要原因。然而，冰川对温室气体排放的反应取决于排放的时间顺序。拟议项目的中心目标是将与冰川有关的区域海平面变化的责任分配到特定的过去排放途径。更具体地说，我们将量化全球冰川的气候敏感性，同时考虑到其对气候系统背景状态的依赖；-计算这种敏感性的空间分布，区分不同的辐射强迫机制（即CO2和其他长寿命温室气体、气溶胶和土地利用变化）；-确定由冰川对气候系统辐射强迫的响应引起的区域海平面变化，再次区分不同的机制；-将有关区域海平面格局的信息与具体的、实际的历史排放途径（例如来自个别国家）结合起来，将与冰川有关的区域海平面变化的责任分配给排放者；-确定由特定排放途径引起的与冰川有关的区域海平面变化的时间演变，最重要的是将已经实现的质量变化与未来承诺的质量变化区分开来；-通过应用全球总辐射强迫来重建相应的全球冰川总质量损失，并将其与冰川观测值进行比较，从而验证该方法。举一个说明性的例子，这些步骤将使我们能够回答以下问题：-鉴于其历史性的排放途径，德国对印度尼西亚与冰川有关的海平面变化负有什么责任？——海平面的变化有多少已经实现，时间的演变是什么样子的？——未来海平面的变化会有多大？时间的演变会是什么样子？-责任分配的不确定性是什么？

Melting glaciers are one of three main contributors to global mean sea-level rise, together with the thermal expansion of sea water and mass loss from the Greenland and Antarctic ice sheets. Over the course of the 20th century, they were more likely than not the dominant cause of sea-level rise. In the coming centuries, mass loss rates for Greenland and Antarctica are projected to increase significantly, while the glaciers’ contribution is limited by their comparatively small size. However, the glacier contribution will remain substantial during the 21st century and non-negligible over at least the coming 300 years. An anthropogenic contribution to glacier mass loss is clearly detectable in the second half of the 20th century, and anthropogenic causes have become the dominant reason for glacier mass loss in recent decades. However, the glaciers’ response to greenhouse gas emissions depends on the temporal sequence of emissions.The central objective of the proposed project is to enable the allocation of responsibility for glacier-related, regional sea-level change to specific past emission pathways.More specifically, we will- quantify the climate sensitivity of the global glacier mass, taking into account its dependence on the background state of the climate system;- calculate the spatial distribution of this sensitivity, differentiating between different mechanisms of radiative forcing (i.e. CO2 and other long-lived GHGs, aerosols and land use change);- determine the regional sea-level change caused by the response of glaciers to radiative forcing of the climate system, again differentiating between different mechanisms;- combine the information about regional sea-level patterns with specific, actual historical emission pathways (e.g. from individual countries) to allocate the responsibility for glacier-related regional sea-level change to emitters;- determine the temporal evolution of glacier-related regional sea-level change caused by a specific emission pathway, most importantly separating between mass change that has been realized and mass change that is committed for the future;- validate the approach by applying global total radiative forcing to reconstruct the corresponding total global glacier mass loss and by comparing it to observations of glaciers.To give an illustrative example, these steps will allow us to answer questions like the following:- What is the responsibility of Germany – given its historic emission pathway – for glacier-related sea-level change in Indonesia?- How much of that sea-level change has already been realized, and what did the temporal evolution look like?- How much of the sea-level change will be realized in the future, and what will the temporal evolution look like?- What are the uncertainties in this allocation of responsibility?