Observational constraints on the global methane budget

摘要

Quantitative understanding of methane sources and sinks is necessary to develop a reasonable strategyto mitigate its potential influence on climate and background air quality.NOAA has measured atmospheric CH4 from a globally-distributed network of background air sampling sites since 1983.The observations are used to provide the following constraints on the global methane budget: 1-Atmospheric burden: the annually averaged global CH4 abundance in 2004 was 1755 ppb,corresponding to a burden of 4860 Tg CH4.2-Global annual emissions: based on a lifetime of 9 years,total emissions have averaged ~550 Tg CHCH4 yr-1 from 1984-2004,with no significant trend.3-Interannual variability in sinks: after the eruption of Mt.Pinatubo in 1991,sharp increases in CH4 and CO growth rates were observed in the tropics and high southern latitudes.Calculations madewith a radiative transfer model show that UV actinic flux in the wavelength region 290-330 nmwas attenuated by about 12% immediately after the eruption because of absorption by SO2,and that the UV flux was perturbed for up to 1 year after the eruption because of scattering by sulfate aerosols.We suggest that decreased OH led to the observed large growth rates of CH4 and CO during late-1991 and early-1992.4-Decreased emissions at high northern latitudes: a decrease in the differencein CHCH4 annual averages between northern and southern polar regions occurred in 1992.Comparison of the observations with CH4 emissions inventories suggest that annual emissionsfrom the fossil fuel sector in the former Soviet Union decreased by ~10 Tg CH4 in the early-1990s.