Three‐dimensional model synthesis of the global methane cycle

TLDR

The study aimed to construct candidate methane budget scenarios based on mass balance and carbon isotope constraints. The authors compiled global emission and sink distributions from measurements and statistics, used 3‑D OH fields and a tracer transport model to simulate atmospheric signatures, and tested scenarios against observed meridional gradients and seasonal variations. Several budget scenarios satisfy all atmospheric constraints; the preferred one estimates annual methane destruction of 450 Tg by OH oxidation and 10 Tg by soil absorption, with emissions of 80 Tg from fossil sources, 80 Tg from domestic animals, 35 Tg from wetlands and tundra poleward of 50°N, and 295 Tg from landfills, swamps, rice fields, biomass burning, and termites, though individual source contributions remain uncertain. References cited include (1990a, b).

Abstract

The geographic and seasonal emission distributions of the major sources and sinks of atmospheric methane were compiled using methane flux measurements and energy and agricultural statistics in conjunction with global digital data bases of land surface characteristics and anthropogenic activities. Chemical destruction of methane in the atmosphere was calculated using three‐dimensional OH fields every 5 days taken from Spivakovsky et al. (1990a, b) . The signatures of each of the sources and sinks in the atmosphere were simulated using a global three‐dimensional tracer transport model. Candidate methane budget scenarios were constructed according to mass balance of methane and its carbon isotopes. The verisimilitude of the scenarios was tested by their ability to reproduce the meridional gradient and seasonal variations of methane observed in the atmosphere. Constraints imposed by all the atmospheric observations are satisfied simultaneously by several budget scenarios. A preferred budget comprises annual destruction rates of 450 Tg by OH oxidation and 10 Tg by soil absorption and annual emissions of 80 Tg from fossil sources, 80 Tg from domestic animals, and 35 Tg from wetlands and tundra poleward of 50°N. Emissions from landfills, tropical swamps, rice fields, biomass burning, and termites total 295 Tg; however, the individual contributions of these terms cannot be determined uniquely because of the lack of measurements of direct fluxes and of atmospheric methane variations in regions where these sources are concentrated.