Observation-constrained sensitivities of Arctic methane emissions to warming

The sensitivity of pan-Arctic (60 to 90°N) natural methane emissions to climate warming lacks direct observational constraints. Long-term atmospheric measurements of methane, which reflect integrated Arctic fluxes and atmospheric transport, show that in the pan-Arctic the autumn-to-winter CH ₄ build-up (as indicated by the “autumn zero crossing date”) is becoming earlier. This advancing trend in autumn zero crossing date is explained by growing natural Arctic CH ₄ emissions in response to climate warming in July, August and September, with a rate of increase of 0.14 ± 0.04 Tg CH ₄ y ⁻² during the period 1998–2020. Atmospheric δ ¹³ C _CH4 observational records allowed us to attribute this increase to 0.08 ± 0.02 Tg CH ₄ y ⁻² from natural biogenic emissions (wetlands, lakes, permafrost soils) and 0.06 ± 0.02 Tg CH ₄ y ⁻² from wildfire emissions. Our results point to a larger warming sensitivity of natural emissions (3.1 ± 0.9 Tg CH ₄ y ⁻¹ per °C) than previous estimates, and potentially a larger positive feedback on climate warming.