NBIA Colloquium: Peter Ditlevsen

Speaker: Peter Ditlevsen (NBI, Copenhagen University)

Title: Warning of a forthcoming collapse of the Atlantic meridional overturning circulation

Abstract: The dramatic prediction of crossing a climate tipping point was published in Nature Communications a month ago. The paper hit the world news in a way unusual for scientific results; It was out in more than 4000 news outlets and has been accessed more than 300.000 times on Natures web portal. In the talk the basic understanding of climate tipping and early warning signals will be explained. The abstract of the paper reads: The Atlantic meridional overturning circulation (AMOC) is a major tipping element in the climate system and a future collapse would have severe impacts on the climate in the North Atlantic region. In recent years weakening in circulation has been reported, but assessments by the Intergovernmental Panel on Climate Change (IPCC), based on the Climate Model Intercomparison Project (CMIP) model simulations suggest that a full collapse is unlikely within the 21st century. Tipping to an undesired state in the climate is, however, a growing concern with increasing greenhouse gas concentrations. Predictions based on observations rely on detecting early-warning signals, primarily an increase in variance (loss of resilience) and increased autocorrelation (critical slowing down), which have recently been reported for the AMOC. Here we provide statistical significance and data-driven estimators for the time of tipping. We estimate a collapse of the AMOC to occur around mid-century under the current scenario of future emissions.

Brief bio-sketch: Peter Ditlevsen is Professor of climate physics at the Niels Bohr Institute. He did his PhD in 1992 at DTU in solid state physics, which he pursued as a post doc at UC Berkeley. Returning to Denmark, he got a position at the Danish Met Office (DMI), which changed his scientific focus to meteorology and climate. After just one year at DMI he moved to the Niels Bohr Institute, where, except for shorter guest researcher visits abroad, he has been since.  He did a Doctoral thesis in Turbulence and Climate Dynamics in 2004, and has contributed to a broad range of topics in turbulence, especially on shell models, chaos and dynamical systems, meteorology and climate and data and time series analysis especially on ice-core records.