Global warming driving increased winter CO<sub>2</sub> emissions in the Northern Hemisphere permafrost region

<p>Global warming accelerates the breakdown of carbon stored in permafrost regions, releasing it into the atmosphere and amplifying climate change, particularly during winter when photosynthesis ceases. The Northern Hemisphere's permafrost is primarily concentrated in two key regions — the Arctic and the Tibetan Plateau — each with distinct environmental characteristics. However, previous studies often treat these regions separately, missing the opportunity to compare their winter CO<sub>2</sub> emissions within a unified framework. Here, we synthesized 2,487 monthly CO<sub>2</sub> flux measurements from 166 in-situ sites to quantify the spatial and temporal variations and key drivers of winter CO<sub>2</sub> emissions in these two regions. Our analysis reveals that combined winter emissions from the Arctic and Tibetan Plateau are estimated to be 1,289 ± 25 Tg C yr<sup>-1</sup>. From 1982 to 2022, winter CO<sub>2</sub> emissions increased by 2.10 ± 0.23 Tg C yr<sup>-1</sup>. Notably, since 2001, winter CO<sub>2</sub> emissions have surged in the Arctic while declining in the Tibetan Plateau. The driving factors also differ: soil temperature dominates in the Arctic (51%), whereas soil moisture plays the most significant role on the Tibetan Plateau (33%). These findings highlight the contrasting mechanisms governing winter carbon emissions in these regions and underscore the importance of incorporating region-specific factors when predicting permafrost-carbon feedbacks in a warming world.</p>