Just How Much Methane is Released in California?

by Emil Morhardt

On the occasional foggy day in Claremont, one can be nearly bowled over by the smell of dairy farms—not a smell that mixes well with the usual orange blossom/eucalyptus fragrance permeating the campus of the Claremont Colleges. The smell is wafting over from the eastern South Coast Air Basin (SoCAB), which, along with California’s Central Valley is the focus of a new top-down estimate of methane emissions by Yuyan Cui  and colleagues at NOAA and the University of Colorado in Boulder, Harvard University, and the University of Michigan. Top-down estimates are based on measurements of methane made from above—in this case by aircraft—rather than based on ground-based considerations, such as counting the number of dairy cows and multiplying by how much methane each is thought to produce. One object of the study was to provide data for use by the State of California in attempting to assure that statewide greenhouse gas emissions not exceed 1990 levels by 2020. The study used some fancy inverse modeling to trace the concentrations measured aloft to their sources, and to calculate that total emission levels. The results corroborated those of several other recent studies, showing that twice as much methane is being emitted than was estimated by the USEPA in 2005, something on the order of 426 Gg (Gigagrams, millions of kilograms) per year. In the eastern SoCAB it, sure enough, is coming from the dairy cattle. In the western SoCAB, where there aren’t any, it comes from landfills, wells, and other un-described point sources. Continue reading