Arctic amplification was strong during past warm events, yet weaker than in recent decades.

Recent observations and model simulations have found that the Arctic has warmed considerably more quickly in recent decades than the rest of the globe, a process known as polar or Arctic amplification (AA). However, the Arctic's behavior during the past warm and cold periods remains less understood, particularly during the last deglacial period (∼21–11.7 thousand years ago (ka)), when atmospheric carbon dioxide (CO₂) concentrations rose by around ∼70–80 parts per million by volume, an increase comparable to human emissions since the Industrial Revolution. We investigate the AA factor over the last deglacial period using a fully coupled ocean–atmosphere simulation (TraCE-21k-II) with the Community Climate System Model version 3 (CCSM3). Our analysis shows that both the Arctic and global surface air temperature and the Atlantic Meridional Overturning Circulation (AMOC) strength varied coherently. A stronger AMOC transported more heat to the Arctic, enhancing both surface air temperature and AA factors. The AA factor was lower (∼1.8 times) during cold periods (e.g., early Heinrich 1 (∼19–17 ka) and the Younger Dryas (∼12.9–11.7 ka)) and increased to ~2.5 times during warm intervals (e.g., late Heinrich 1 (∼17–14.9 ka) and the onset of the Holocene (∼11.7–9.4 ka)). The highest AA (∼3 times) occurred during the Bølling–Allerød warm phase (∼14.9–12.9 ka), yet remained below modern observational estimates (∼4 times; Rantanen et al., 2022). These findings highlight that in the past, the Arctic warmed faster than the global average, particularly during warm phases, such that AA is a persistent but variable feature of past climate transitions. Since AA drives Arctic sea ice loss, it can weaken ice–albedo and modify lapse-rate feedbacks and trigger broader atmospheric and oceanic changes, thereby affecting regional and global climate systems.