Xin Lan (NOAA & CU Boulder CIRES)

INSTAAR Seminar Series. Hybrid event, in person and via Zoom

Location: SEEC S372A, Third-floor conference center adjacent to Earth Lab offices. 4001 Discovery Drive, Boulder, CO

Audience: All are welcome

After presentation: There will be time for informal discussion with the speaker after the presentation; cookies and coffee will be served.

Abstract: 

NOAA Global Monitoring Laboratory operates a cooperative global measurement network for Long-lived Greenhouse Gases (LLGHG) to determine their large-scale spatial and temporal distributions. The goal of this network is to provide LLGHG measurements as precisely and accurately as possible to inform long-term changes in emissions and sinks. Systematic measurements of atmospheric methane (CH4) were started in 1983. From these measurements, we learn that the atmospheric burden of CH4 increased rapidly until 1999 when it reached a plateau. However, this stabilization period didn’t last long and the global CH4 increase restarted again in 2007 and further accelerated in recent years. Around the same time that the increase started, the ratio of stable carbon isotopes of CH4 (13C/12C), denoted by δ13C-CH4, started to decrease after two centuries of increase, according to the NOAA/INSTAAR measurements.

Atmospheric methane's rapid growth from 2007 to the present is unprecedented in the observational record, in equivalent to a 100 Tg/yr increase in the annual total CH4 emissions from the 560 Tg/yr average during the stabilization period if we assume an almost constant atmospheric CH4 lifetime. The decreasing trend in δ13C-CH4 implies the growth is mainly driven by an increase in biogenically-sourced emissions, while increase in fossil fuel emission only accounts for about 15% of recent increase. Although microbial emissions from agricultural and waste have increased between 2007-2022 by perhaps 35-40 Tg/yr according to bottom-up inventories, another 35-40 Tg/yr of the recent net growth in CH4 emissions may have been driven by natural biogenic processes, especially wetland from the tropics as feedbacks to climate change.

A new modelling comparison between methane's growth and isotopic shift in the 15 years from 2007-2022, and the transitions from glacial to interglacial periods in the Pleistocene, shows that the modern event may be comparable to or greater in scale and speed than methane's growth and isotopic shift during past glacial/interglacial termination events. Is the similarity between current CH4 growth and ice core CH4 records during glacial/interglacial termination event suggesting a global-scale climate reorganization is under way?