Theoretical and paleoclimatic evidence for abrupt transitions in the Earth system

Abstract

Specific components of the Earth system may abruptly change their state in response to gradual changes in forcing. This possibility has attracted great scientific interest in recent years, and has been recognized as one of the greatest threats associated with anthropogenic climate change. Examples of such components, called tipping elements, include the Atlantic Meridional Overturning Circulation, the polar ice sheets, the Amazon rainforest, as well as the tropical monsoon systems. The mathematical language to describe abrupt climatic transitions is mainly based on the theory of nonlinear dynamical systems and, in particular, on their bifurcations. Applications of this theory to nonautonomous and stochastically forced systems are a very active field of climate research. The empirical evidence that abrupt transitions have indeed occurred in the past stems exclusively from paleoclimate proxy records. In this review, we explain the basic theory needed to describe critical transitions, summarize the proxy evidence for past abrupt climate transitions in different parts of the Earth system, and examine some candidates for future abrupt transitions in response to ongoing anthropogenic forcing. Predicting such transitions remains difficult and is subject to large uncertainties. Substantial improvements in our understanding of the nonlinear mechanisms underlying abrupt transitions of Earth system components are needed. We argue that such an improved understanding requires combining insights from (a) paleoclimatic records; (b) simulations using a hierarchy of models, from conceptual to comprehensive ones; and (c) time series analysis of recent observation-based data that encode the dynamics of the present-day Earth system components that are potentially prone to tipping.

Statistical precursor signals for Dansgaard-Oeschger cooling transitions

“…Paleoclimate evidence supports that abrupt climate changes due to crossing tipping points actually occurred in the past 2,[4][5][6] . Recent observational and modelling evidence suggest the existence of climate tipping elements in the present Earth, which pose arguably one of the greatest risks in the context of anthropogenic global warming 1,2 . The Atlantic Meridional Overturning Circulation (AMOC) is considered the most important global-scale tipping element 1,2,6 .…”

“…A tipping point is a threshold in a forcing or control parameter, at which a small additional perturbation causes a qualitative change in the state of the system under consideration 1 . Once a tipping point is passed, a system can transition abruptly to an alternative stable or oscillatory state 2 . The existence of climate tipping points and the possibility of abrupt transitions had been theoretically predicted since the early 1960s 2,3 .…”

“…Once a tipping point is passed, a system can transition abruptly to an alternative stable or oscillatory state 2 . The existence of climate tipping points and the possibility of abrupt transitions had been theoretically predicted since the early 1960s 2,3 . Paleoclimate evidence supports that abrupt climate changes due to crossing tipping points actually occurred in the past 2,[4][5][6] .…”

“…The existence of climate tipping points and the possibility of abrupt transitions had been theoretically predicted since the early 1960s 2,3 . Paleoclimate evidence supports that abrupt climate changes due to crossing tipping points actually occurred in the past 2,[4][5][6] . Recent observational and modelling evidence suggest the existence of climate tipping elements in the present Earth, which pose arguably one of the greatest risks in the context of anthropogenic global warming 1,2 .…”

“…Recent observational and modelling evidence suggest the existence of climate tipping elements in the present Earth, which pose arguably one of the greatest risks in the context of anthropogenic global warming 1,2 . The Atlantic Meridional Overturning Circulation (AMOC) is considered the most important global-scale tipping element 1,2,6 . Recent studies have inferred that the AMOC is currently at its weakest in at least a millennium 7,8 ; projections of the AMOC strength in the next hundred years are model-dependent, but the declining AMOC trend is projected to continue in the coming century 9 .…”