Moderate Climate Overshoots Trigger Hysteresis in Arctic Sea Ice

Abstract Limiting global warming to 1.5°C above preindustrial levels is central to the Paris Agreement, yet temporary overshoots of this target are increasingly likely. While the global mean surface temperature could return to 1.5°C through mitigation and carbon dioxide removal, the regional consequences of overshoot remain uncertain. We use the UK Earth System Model (UKESM1.0-LL) to compare a policy-relevant moderate overshoot scenario—peaking at 1.8°C before cooling to 1.5°C by 2100—with a no-overshoot pathway. We show that, despite similar global temperatures by 2100, the Arctic exhibits significant hysteresis, with ~ 18% less sea ice and ~ 1°C higher near-surface temperatures under overshoot. Using a zonal energy balance model and radiative kernel analysis, we identify sea ice–albedo and lapse rate feedbacks as dominant drivers of this, while heat transport plays a minor role. These findings provide the first mechanistic attribution of Arctic hysteresis under a moderate overshoot scenario, highlighting the risks of delayed mitigation and the importance of avoiding even temporary exceedance of temperature targets.