Intensified Positive Arctic–Methane Feedback under IPCC Climate Scenarios in the 21st Century

Abstract

The positive Arctic–methane (CH4) feedback forms when more CH4 is released from the Arctic tundra to warm the climate, further stimulating the Arctic to emit CH4. This study utilized the CLM-Microbe model to project CH4 emissions across five distinct Arctic tundra ecosystems on the Alaska North Slope, considering three Shared Socioeconomic Pathway (SSP) scenarios using climate data from three climate models from 2016 to 2100. Employing a hyper-resolution of 5 m × 5 m within 40,000 m2 domains accounted for the Arctic tundra’s high spatial heterogeneity; three sites were near Utqiaġvik (US-Beo, US-Bes, and US-Brw), with one each in Atqasuk (US-Atq) and Ivotuk (US-Ivo). Simulated CH4 emissions substantially increased by a factor of 5.3 to 7.5 under the SSP5–8.5 scenario compared to the SSP1–2.6 and SSP2–4.5 scenarios. The projected CH4 emissions exhibited a stronger response to rising temperature under the SSP5–8.5 scenario than under the SSP1–2.6 and SSP2–4.5 scenarios, primarily due to strong temperature dependence and the enhanced precipitation-induced expansion of anoxic conditions that promoted methanogenesis. The CH4 transport via ebullition and plant-mediated transport is projected to increase under all three SSP scenarios, and ebullition dominated CH4 transport by 2100 across five sites. Projected CH4 emissions varied in temperature sensitivity, with a Q10 range of 2.7 to 60.9 under SSP1–2.6, 3.8 to 17.6 under SSP2–4.5, and 5.7 to 17.2 under SSP5–8.5. Compared with the other three sites, US-Atq and US-Ivo were estimated to have greater increases in CH4 emissions due to warmer temperatures and higher precipitation. The fact that warmer sites and warmer climate scenarios had higher CH4 emissions suggests an intensified positive Arctic–CH4 feedback in the 21st century. Microbial physiology and substrate availability dominated the enhanced CH4 production. The simulated intensified positive feedback underscores the urgent need for a more mechanistic understanding of CH4 dynamics and the development of strategies to mitigate CH4 across the Arctic.