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

2019 - 2022

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?

Funding Agency: 
Deutsche Forschungsgemeinschaft (DFG)
Funding Amount: 
€302 000