Early Warning Signs for Abrupt Transitions
The workshop "Early Warning Signs for Abrupt Transitions" is organized by Peter Ashwin, University of Exeter, Niklas Boers, Potsdam Institute for Climate Impact Research, and Kerstin Lux, Technical University of Munich. It will take place as an online event under the EU Horizon 2020 funded project "TiPES – Tipping Points in the Earth System". Also, non-TiPES members are invited to participate. Please register below.
Aim and Scope
Several subsystems of the earth might undergo abrupt transitions under sustained global warming. Predicting such a tipping event is a very complex task, and the detection of Early Warning Signs (EWS) is an active field of research.
Despite their importance in predicting abrupt transitions, their extraction from data is a challenging task. False positives, i.e. the increase in variance or lag-1 autocorrelation that is not followed by an abrupt transition, reduce the predictive power of such statistical precursor signs. Promising recent results on alternative indicators will be presented and discussed.
Furthermore, many previous results on EWS assume that the underlying noise follows a Brownian Motion. However, it might well be that there is a non-negligible time-correlation structure within the noise in the data. We will discuss how the type of noise affects the EWS.
We would like to present recent results on Early Warning Signs and discuss challenges in advancing the theory and application of EWS.
October 13, 2021, 1-5 pm CEST
Detailed information will be announced here in due course.
Towards a resilience sensing system for the biosphere (Tim Lenton)
We are in a climate and ecological emergency, where dangerous anthropogenic interference with the biosphere is risking abrupt and/or irreversible changes. To make it easier to see where things are going wrong, and to see where deliberate interventions are making things better, we propose a biosphere resilience sensing system, utilizing the generic mathematical behavior of complex systems: Loss of resilience corresponds to slower recovery from (and a larger response to) perturbations, gain of resilience equates to faster (and smaller) responses to perturbations. Such behavior can be monitored both in time (as described) and across space. We focus here on the potential for satellite remote sensing to provide global spatial coverage and high temporal resolution resilience sensing, particularly of the terrestrial biosphere.
Critical Slowing down in reconstructions of Greenland Ice Sheet Melt Rates and the strength of the AMOC (Niklas Boers)
Several subsystems of the Earth have been suggested to exhibit the potential to abruptly transition to alternative states. A formalism that might be suitable to describe such events is that of dynamical systems and especially bifurcation theory. Considering abrupt regime shifts of climate subsystems as bifurcation-induced transitions suggests they might be preceded by critical slowing down, which could be used as an early-warning signal. Here I show that critical slowing down can be detected in 1) height reconstructions from the central-western part of the Greenland ice sheet and 2) in sea-surface temperature and salinity based fingerprints of the Atlantic Meridional Overturning Circulation.
Arctic summer sea-ice loss will accelerate in coming decades (Anna Poltronieri)
Every year, the area of the Arctic sea-ice decreases in the boreal spring and summer and reaches its yearly minimum in the early autumn.
In the CMIP6 ensemble, we find that the majority of the models that reach an Arctic sea-ice free state in the SSP585 runs shows an accelerated loss of sea-ice for the last degree of warming compared to the second last degree of warming, which implies an increased sensitivity of the sea-ice to temperature changes.
As a result of accelerated sea-ice loss, the average evolution of the sea-ice area among the CMIP6 models before the loss of the summer sea-ice shows an increase in the year-to-year fluctuations in minimum ice cover in the next decade.
Early Warning Signs for Systems driven by Time-Correlated Noise Processes (Kerstin Lux)
Some subsystems of the Earth have been identified to be at risk of undergoing critical transitions.
From the theory of stochastic fast-slow systems , it is known that approaching such a tipping point goes along with an increase of variance and/or autocorrelation fluctuations if the noise term is represented by a Brownian motion. However, it is well-known that noise present in many climate systems shows time-correlation.
Therefore, in this talk, I will address Early Warning Signs (EWS) for stochastic fast-slow systems driven by colored noise, fractional Brownian motion and the Rosenblatt process . Our results show that, for colored noise, there is no variance increase at all, so the type of noise can make us "blind" for tipping.
 C. Kuehn. A Mathematical Framework for Critical Transitions: Normal Forms, Variance and Applications. J. Nonlinear Sci., 23(3):457–510, 2013.
 C. Kuehn, K. Lux, and A. Neamtu. Warning Signs for Non-Markovian Bifurcations: Color Blindness and Scaling Laws. arXiv:2106.08374, pages 1–14, 2021.
Registration is mandatory but free of charge.