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INSTAAR Seminar: Dr. Xin Lan - Improved Constraints on Global Methane Emissions and Sinks...

Monday, February 28, 2022, 12:00PM - 1:00PM

INSTAAR Seminar: Dr. Xin Lan - Improved Constraints on Global Methane Emissions and Sinks…

Speaker

Dr. Xin Lan

NOAA Global Monitoring Lab

Location:

Sievers Conference Room, SEEC S228

4001 Discovery Drive, Boulder, CO

Please join us Monday February 28 (in-person and remote format) at 12:15 pm for the INSTAAR Noon Seminar. We will get to hear from Dr. Xin Lan (NOAA Global Monitoring Lab). Cookies and coffee will be served during the talk in the Sievers Conference Room.

The title of her talk:

 

Improved Constraints on Global Methane Emissions and Sinks Using Stable Carbon Isotopes of Methane

Dr. Lan will be available to meet after her talk til ~4:30PM MST. Please email Syliva E. Michel (sylvia.michel@colorado.edu) directly to set up a time to meet with the speaker. The seminar will be held in hybrid format, in person in the Sievers Room and via Zoom:

Zoom link: https://cuboulder.zoom.us/s/94699942840
Password: noon2021

 

Improved Constraints on Global Methane Emissions and Sinks Using Stable Carbon Isotopes of Methane

 

Abstract: The atmospheric burden of methane (CH4) has been increasing since 2007 after a relatively stable period from 1999 to 2006, but the reasons behind are still debated. 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. We use these observations to study the drivers behind the global atmospheric CH4 increase after 2006. Candidate emission and sink scenarios are constructed based on proposed hypotheses in the literature, and long-term mass balance constraint from δ13C-CH4. These scenarios are simulated in the TM5 tracer transport model for 1984–2016 to produce three-dimensional fields of CH4 and δ13C-CH4, which are compared with observations to test the competing hypotheses in the literature in one common model framework. We find that the fossil fuel (FF) CH4 emission trend from the Emissions Database for Global Atmospheric Research 4.3.2 inventory does not agree with observed δ13C-CH4. Increased FF CH4 emissions are unlikely to be the dominant driver for the post-2006 global CH4 increase despite the possibility for a small FF emission increase. We also find that a significant decrease in the abundance of hydroxyl radicals (OH), the primary CH4 sink, cannot explain the post-2006 global CH4 increase since it does not track the observed decrease in global mean δ13C-CH4. Emission increases from microbial sources (from anthropogenic sources and natural wetlands) are mostly likely the dominant contributors.

 

Different CH4 sinks have different fractionation factors for δ13C-CH4, thus we can investigate the uncertainty introduced by the reaction of CH4 with tropospheric chlorine (Cl), a CH4 sink whose abundance, spatial distribution, and temporal changes remain uncertain. Our results show that including or excluding tropospheric Cl as a 13 Tg/year (~2% of total) CH4 sink in our model changes the magnitude of estimated fossil emissions by ∼20%. We also found that by using different wetland emissions based on a static versus a dynamic wetland area map, the partitioning between FF and microbial sources differs by 20 Tg/year, ∼12% of estimated fossil emissions. This study highlights the capability of δ13C-CH4 measurements, and points to the way forward to improve our understanding of the evolving global CH4 budget.


Please feel free to forward this to colleagues who may be interested in attending.