Project Funding: 2017 - 2020

NRA: 2016 NASA: Interdisciplinary Research in Earth Science   

Funded by NASA

Abstract:
We propose an InterDisciplinary Research in Earth Science (IDS) investigation to quantify the sources of atmospheric methane, interpret recent decadal trends, and characterize biogeochemical process drivers in order to enable future projections of atmospheric methane. The work will involve the interpretation of 2003-present satellite and suborbital records of atmospheric methane using state-of science inverse methods supported by new bottom-up emission inventories and biogeochemical models (including for ocean margins). There are at present very large uncertainties in bottom-up estimates of methane sources, stifling the attribution of decadal trends in atmospheric methane and hindering the development of climate policy. Atmospheric observations from the current suborbital observing network are too sparse to constrain the relative contributions of different anthropogenic and natural sources or of the OH radical sink. Here we will construct new gridded emission inventories for anthropogenic and natural methane sources, to enable improved inversions of atmospheric data and attribution of inversion results to specific sources. Natural inventories for wetlands and the oceans will rely on biogeochemical models constrained by satellite surface data (i.e, NASA MEaSUREs inundation datasets, MODIS). MODIS burned areas and MOPITT derived CO will be used to construct a biomass burning inventory for methane. We will use these inventories as priors in a global inversion of atmospheric methane data from the GOSAT satellite (2009-present) to gain new insights into the processes controlling the methane budget and its decadal trend, and to falsify hypotheses regarding that trend. We will use a new retrieval of methane from the SCIAMACHY satellite instrument (2003-2009), stitched with the GOSAT record, to extend the trend analysis and identify the sources responsible for the 2006 onset of renewed methane growth. We will use new satellite observations from TROPOMI with daily global coverage to refine understanding of the current methane budget. We will further generate a new lower-tropospheric methane product by combining TROPOMI and CrIS Level 2 methane to gain unique new insights into high-latitude and coastal sources. Results from our inverse analyses will be used with a Bayesian fusion approach to attribute emissions and trends to specific source sectors and to guide the improvement of bottom-up inventories and the underlying biogeochemical models. We will employ a range of biogeochemical proxies, including equivalent water height from GRACE, temperature, carbon uptake (from GOME-2, GOSAT, OCO-2), to quantify wetland CH4 emissions sensitivity to climate variability and the associated carbon-climate feedbacks, with a particular emphasis on biogeochemical controls on wetland emission IAV in the context of tropical climatic extremes and increasing temperatures in high-latitude ecosystems. In this manner our work will provide support for climate policy directed at anthropogenic methane and will increase understanding of the biogeochemical drivers of natural sources, thus allowing assessments of climate feedbacks and enabling future projections of atmospheric methane.