Atmospheric Methane: Comparison Between Methane's Record in 2006-2022 and During Glacial Terminations

Atmospheric methane's rapid growth from late 2006 is unprecedented in the observational record. Assessment of atmospheric methane data attributes a large fraction of this atmospheric growth to increased natural emissions over the tropics, which appear to be responding to changes in anthropogenic climate forcing. Isotopically lighter measurements of delta(13)C(CH4 )are consistent with the recent atmospheric methane growth being mainly driven by an increase in emissions from microbial sources, particularly wetlands. The global methane budget is currently in disequilibrium and new inputs are as yet poorly quantified. Although microbial emissions from agriculture and waste sources have increased between 2006 and 2022 by perhaps 35 Tg/yr, with wide uncertainty, approximately another 35-45 Tg/yr of the recent net growth in methane emissions may have been driven by natural biogenic processes, especially wetland feedbacks to climate change. A model comparison shows that recent changes may be comparable or greater in scale and speed than methane's growth and isotopic shift during past glacial/interglacial termination events. It remains possible that methane's current growth is within the range of Holocene variability, but it is also possible that methane's recent growth and isotopic shift may indicate a large-scale reorganization of the natural climate and biosphere is under way.

Automated summary

The rapid growth of atmospheric methane since late 2006 is unprecedented. Increased natural emissions over the tropics, likely in response to anthropogenic climate forcing, have been attributed to a large fraction of this atmospheric growth. Isotopically lighter measurements of delta(13)C(CH4) suggest that the recent increase in atmospheric methane is primarily driven by increased emissions from microbial sources, especially wetlands. The global methane budget is currently imbalanced and new inputs are poorly quantified. While microbial emissions from agriculture and waste sources may have increased between 2006 and 2022 by about 35 Tg/yr, there is also a possibility that another 35-45 Tg/yr of the recent net growth in methane emissions is driven by natural biogenic processes, particularly wetlands responding to climate change. Model comparisons indicate that recent changes may be comparable or even greater in scale and speed than methane's growth and isotopic shift during past glacial/interglacial termination events. It is uncertain if methane's current growth falls within the range of Holocene variability, but it is also possible that the recent growth and isotopic shift of methane may indicate a large-scale reorganization of the natural climate and biosphere.