Skip to main content

Constraining large-scale climate feedbacks in the Earth system using paleo data

Periodic Reporting for period 1 - CONCLIMA (Constraining large-scale climate feedbacks in the Earth system using paleo data)

Reporting period: 2017-07-01 to 2019-06-30

Global warming will have a large impact on humanity’s future. However, many feedbacks between different components of the Earth system at the global scale are not well understood and thus represent some of the largest sources of uncertainty in climate projections. Using a combined data analysis and modelling approach, the goal of CONCLIMA is to investigate past interactions between three key coupled elements in the Earth system: the continental ice sheets, global oceanic circulation and the global carbon cycle. This analysis will address open questions related to the deglaciation of the Northern Hemisphere ice sheets, abrupt changes in ocean circulation and global climate sensitivity, as well as provide constraints on the strength of large-scale climate feedbacks. This project will therefore lead to new insight into the physical mechanisms behind long-term climate changes and lay the foundation for more robust climate projections.
The first part of the project was focused on model development, to have the tools necessary to be able to investigate the scientific questions. It became clear that current generation ice-sheet models would not be adequate for our simulations, so significant effort was made to improve our ice-sheet model. This effort led to improved model physics, a better user interface and ability to couple it easily with other models. In parallel, we worked with collaborators in Germany to couple the ice-sheet model to the fast, global climate model CLIMBER-X. Preliminary tests show that the model is capable of running glacial cycle simulations in several hours of computational time. We also focused on understanding how the Northern Hemisphere ice sheets react when forced by climatic and oceanic temperature perturbations, since this type of interaction is critical to large-scale climate feedbacks. A new analysis of the Atlantic Meridional Overturning Circulation (AMOC) was also performed, which helped to quantify the sensitivity of the oceanic circulation to climatic changes.
The ice-sheet model developed in the context of the project, really advances our capability to perform large-ensemble, glacial cycle simulations of the ice sheets. It is designed to facilitate broad testing of both parameter values and different parameterizations. Furthermore, it will be easy to incorporate new model physics as our understanding of the importance of different processes improves. We used the model to show that interactions between the Greenland ice sheet and the ocean are critical to its evolution on glacial time scales, something that has not been accounted for in simulations until now.

The analysis of the AMOC performed with collaborators in Germany showed that the oceanic circulation is already slowing down, most likely as a consequence of global warming. The results of our study were confirmed by an independent analysis that came out at the same time. Therefore, confidence in the` results is very high, and this slowdown has broad implications for society as a whole. The Atlantic circulation plays an important role in the redistribution of heat globally, particularly bringing warm water from the equator towards the North Atlantic, which has a stabilizing effect on the European climate. It is not known what the long-term impacts of such a slowdown, and potential shutdown, of the circulation will be, but our study makes it clear that understanding the system better is an urgent and high priority issue.
Tabone et al. (2018): Greenland ice sheet volume from the Last Glacial Maximum until today