Update: Methane Up in the Air
by Bill Chameides | December 2nd, 2008
posted by Erica Rowell (Editor)
Though methane is a naturally occurring greenhouse gas, things like landfills, rice paddies, and deforestation increase methane emissions.
Here’s an update on the sudden uptick in the concentration of atmospheric methane, a potent greenhouse warmer.
Before we dig into the update, though, let me provide some background and context.
Methane is a potent greenhouse gas: pound for pound it is about 25 times more effective as a global warmer than carbon dioxide (CO2). Although it occurs naturally in the atmosphere, for example as a result of decay from organic material in swamps and other wetlands, human activities (such as growing rice, raising cows, cutting down forests, building up landfills, and mining coal) can also send methane into the atmosphere. (Here’s more on methane from wikipedia.)
Throughout much of the late nineteenth and twentieth centuries, methane concentrations increased quite substantially: more than a factor of 2, from about 0.8 to 1.8 part per million (ppm). But overall methane levels are considerably less than CO2 levels (~380 ppm). That is why even though methane rose more than CO2 and each methane molecule warms more than a CO2 molecule, the total warming from the methane increase is only about one fifth the warming from CO2.
Nevertheless, that’s a lot of warming. And given methane’s potency as a global warmer, it was a great relief to scientists when methane concentrations appeared to stabilize in the late 1990s.
But back in June, I reported on some preliminary data showing that methane concentrations had begun to inch up again in 2007. Well, that preliminary report has now been confirmed in a peer-reviewed article published in Geophysical Research Letters. Using data from a network of surface-sampling sites around the globe, Matthew Rigby and his colleagues at the Massachusetts Institute of Technology estimate that methane concentrations are now increasing with a current growth rate of about one half a percent per year. This rate of increase is smaller than the rate prior to the recent stabilization, but still significant.
What is behind the renewed uptick, and will the rise prove to be a short-lived perturbation or the start of a long-term trend? We don’t yet know. But stay tuned. We’ll keep you posted on what the research turns up.filed under: carbon dioxide emissions, faculty, global warming, methane, science
and: greenhouse gases, research