Arctic Hysteresis Under a Moderate Climate Overshoot

Failure to meet temperature targets through policy inaction can lead to climate overshoots, scenarios where global mean surface temperature (GMST) exceeds a target in the short term but returns below it later through deployment of negative emissions technologies. The magnitude and impacts of these pathways are poorly quantified-to-date, yet current rates of both greenhouse gas emissions and technological innovation suggest these scenarios are a possible future realization. Although technological advances could enable decarbonization in a few decades, the initial warming has the potential to trigger positive feedbacks and hysteresis in the climate system that could be avoided by staying under a temperature target such as 1.5 ºC above pre-industrial levels as detailed in the Paris Agreement. Overshoot scenarios are an important possible future climate pathway, yet their potential impacts are not well understood. Here, simulations of a possible overshoot scenario over the 21st century from the U.K. Earth System Model, UKESM1, were analyzed in comparison to a control no-overshoot scenario to determine the climate impacts of a parabolic temperature trend. Initial results demonstrate that the Arctic exhibits noticeable hysteresis; warmer temperatures and sea ice loss from a mid-century peak warming of 1.9 ºC above pre-industrial persist despite GMST returning to 1.4 ºC above pre-industrial by 2100. To better understand the mechanisms behind these Arctic impacts, we employed a radiative feedback and energy balance analysis that revealed positive sea ice albedo and lapse rate feedbacks as the major drivers of this strong regional response. These insights deepen our understanding of the earth system and provide further impetus to the importance of rapid mitigation in avoiding long-term climate impacts. Further analysis will focus on possible teleconnections between such polar amplification and mid-latitude weather and climate through changes in climate modes such as the Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and the Atlantic Meridional Overturning Circulation (AMOC).