ESE Trailblazer Symposium

Climate policies are often designed to limit greenhouse gas concentrations or globally averaged surface warming to a certain threshold (e.g., 1.5°C). However, what the global climate looks like at such a target may depend not only on the level of global warming, but also on how quickly greenhouse gases were increased to achieve that level. This raises the question: for a fixed amount of greenhouse gas increase, how does the global climate system respond to different rates of increase? In this talk, I will address this question in the case of the Atlantic Meridional Overturning Circulation (AMOC), an important large-scale ocean circulation that is projected to weaken under anthropogenic climate change. Using a series of fully-coupled global climate model simulations, I show that meltwater from Arctic sea ice strongly modulates the AMOC's response to different atmospheric CO2 rates of change by acting as both a forcing and a feedback on the circulation's weakening. These processes cause the AMOC to weaken more under faster rates of CO2 increase, leading to a variety of downstream impacts that merit policy attention and further study.