Permafrost tipping point triggered by warming-driven loss of old carbon.
basic_science · Level V
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- Record sourced from PubMed, PMID 41997934.
- Also identified by DOI 10.1038/s41467-026-72122-3.
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Abstract
Permafrost carbon vulnerability, particularly concerning temperature thresholds and old carbon mobilization, remains a critical uncertainty in climate projections. Through a five-year, multi-level warming experiment on the Tibetan Plateau, we investigate these dynamics using >40,000 hourly flux measurements combined with vertical CO<sub>2</sub> concentration and δ<sup>13</sup>C-CO<sub>2</sub> profiling. Here we demonstrate under low-to-moderate warming (<2 °C), respiratory carbon loss (R<sub>eco</sub>) increments exceed photosynthetic carbon uptake (GPP) gains by 1-16 fold, driving a quantitative shift toward ecosystem carbon source. Extreme warming (2-4 °C) triggers a surge in growing-season deep carbon loss to 59% R<sub>eco</sub>, while GPP declines precipitously. The decoupling between R<sub>eco</sub> and GPP drives a qualitative transition to strong carbon source, implying the existence of a tipping point within 2-4 °C. Projected to end-of-century warming levels (2.69 °C) across Tibetan permafrost regions, this could release 24-47 g CO<sub>2</sub> m<sup>-2</sup> yr<sup>-1</sup> old carbon. These findings establish quantitative thresholds for permafrost carbon vulnerability and inform carbon-climate feedback projections in global cold regions.