A stable Arctic amplification ratio in long-term transient simulation over the last 21,000 years

Arctic amplification (AA), the disproportionate Arctic warming versus hemispheric or global averages, impacts mid-latitude climate. Prior studies reported a wide range of AA ratios from 1.0 to 12.5, based on 20th-century observations or climate model hindcasts. This study investigates the variability of the AA ratio within a long-term transient simulation encompassing the past glacial-interglacial period. We find a strong link between the AA phenomenon and North Atlantic sea ice changes driven by ice-albedo feedback, yielding a stable AA ratio of 2.5 ± 0.8 throughout the last 21,000 years. The current observed AA ratio, slightly lower than 2.5, indicates the combined effect of sea ice melt-induced AA added to the greenhouse gas-induced global warming. We hypothesize that as Arctic sea ice rapidly diminishes, or even disappears, the sea ice-induced AA phenomenon will weaken substantially, reflected in the AA ratio approaching 1.0 within the next 1–2 centuries, even as global warming persists.