A study suggests that increasing rates of ice melt may lead to collapse of ocean circulation. With greenhouse gas concentrations increasing, several elements of the global climate system are at risk of crossing a tipping point that would lead to abrupt, irreversible change. Such catastrophic transitions can occur when a parameter changes faster than a certain rate, even if the parameter's actual value never crosses a critical threshold. This phenomenon is known as rate-induced tipping. Using a model of global ocean circulation, Johannes Lohmann and Peter Ditlevsen demonstrated the possibility of rate-induced collapse of the Atlantic Meridional Overturning Circulation (AMOC) due to polar ice melting. The model predicted that the AMOC would collapse if the freshwater influx from ice melt exceeded a critical level. Yet, even if the freshwater influx never exceeded this threshold, the AMOC could still collapse if the influx increased rapidly. There was no well-defined critical rate of increase separating collapsing from noncollapsing scenarios, given that the system's chaotic dynamics make it highly sensitive to the initial AMOC strength. The results suggest that the range of Earth system parameters that avoids tipping points may be smaller than expected and difficult to predict, according to the authors.
Article #20-17989: "Risk of tipping the overturning circulation due to increasing rates of ice melt," by Johannes Lohmann and Peter D. Ditlevsen.
MEDIA CONTACT: Johannes Lohmann, Niels Bohr Institute, University of Copenhagen, DENMARK; tel: +45-52803543; email: johannes.lohmann@nbi.ku.dk
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Proceedings of the National Academy of Sciences