A fixed methane filter maximizes freshwater emissions under warming
- Sarah F. Harpenslager
- Kate Randall
- Yizhu Zhu
- Michelle C. Jackson
- Ian Sanders
- Bruno Gallo
- Danielle Harris
- Hannah Prentice
- Yulia V. Bespalaya
- Olga V. Aksenova
- Alexander Milner
- Tom C. Cameron
- Boyd A. McKew
- Eoin J. O’Gorman
- Gabriel Yvon-Durocher
- Nikolai Friberg
- Kevin J. Purdy
- Guy Woodward
- Alex J. Dumbrell
- Mark Trimmer
2026-06-05
Approximately half of all methane (CH 4 ) emissions come from freshwaters, where they are regulated by the microbial ‘CH 4 filter’ whose efficiency describes the fraction of CH 4 produced that is subsequently oxidized back to CO 2 (methanotrophy) before emission. How the CH 4 filter efficiency responds to natural warming over centuries or millennia remains unknown. Here we address this question using a natural experiment comprising high-latitude, geothermally warmed streams in five regions spanning the Northern Hemisphere. CH 4 production becomes more efficient with warming, linked to increased abundance of methanogens and underpinned by community shifts. In contrast, while CH 4 oxidation activity increases, its process-level efficiency does not, and methanotrophs shift towards less efficient taxa. Consequently, the system-level CH 4 filter efficiency remains fixed, and CH 4 emissions increase. If this fixed CH 4 filter efficiency under warming is common to freshwaters worldwide (wetlands, lakes and rivers), then an upward trajectory for CH 4 emissions through future climate change appears inevitable.