Atmospheric Methane Has Hit Record Levels, and It’s Not Totally Clear Why

Cows produce an enormous amount of methane. Image: Flickr/Emmett Tullos

Global methane emissions are going up, but no one’s exactly sure why. On its face, it’s an interesting example of how difficult tabulating anything on a global scale can be. But as a rather effective greenhouse gas, any increase in methane concentrations makes for real climate concerns. 

From the early 1980s through 1992, methane emissions increased by about 12 parts per billion per year, but by 2006, growth in methane emissions came to a halt, and even started decreasing. Since then, researchers have seen a “sudden growth” of about 6 parts per billion per year, noted in the journal Science, that has pushed methane levels in the atmosphere to the highest they’ve ever been. 

Methane is a gas that climate scientists would love to target. Unlike carbon, which can persist in the atmosphere for hundreds or thousands of years, methane stays in the atmosphere for between 8 and 12 year. It’s also a more powerful contributor to climate change than carbon—the Intergovernmental Panel on Climate Change says that, over a 100-year time scale, methane traps 34 times as much heat as carbon dioxide—which might make cutting methane emissions a good short-term method of curbing climate change. 

“It’s a very good target to bring down because a lot of the emissions come from gas leaks, which are bad for business anyway,” said Euan Nisbet, author of the Science report and a University of London professor who studies the subject. “You don’t have to change a lot of the human economy, so reducing it is less costly and politically more amenable.”

Methane concentrations in the atmosphere. Image: Science

That is, if Nisbet and other atmospheric scientists can figure out exactly why methane emissions are rising. According to the paper, none of the standard climate models can account for why methane has started increasing again, and measuring methane leaks at the source is tough.

The “bottom up” methane estimates don’t line up with what Nisbet has measured, which is showing a much higher methane increase than those estimates call for. Nailing down the exact reasons is difficult: Unlike carbon emissions—the sources of which are obvious and well understood—much of the increase in methane emissions is believed to be at least partly from natural sources, not mechanical ones, which can be harder to trace.

The major sources of methane include emissions associated with raising cows, natural gas pipeline leaks, coal mining, and landfills. But not every cow and not every landfill is made alike.

Estimating methane emissions from cattle in the United States, for instance, is pretty easy because many are fed a similar diet and live in similar conditions. Measuring cattle emissions in South Sudan, India, and Argentina, which have some of the highest cow populations in the world, on the other hand, is a different proposition.

“A lot of the estimates are done on western cows that drink a lot of water and eat a lot of food. How much work is being done in Sudan, for instance? Not a lot,” he said. “African cows probably emit a lot less methane, but we don’t know how much less.”

Worldwide cattle population by country, 2003. Image: United Nations Food and Agriculture Organization.

Then there are the completely natural processes, which can have an assist from manmade global warming. Methane isn’t called “swamp gas” for nothing: Nisbet believes that much of the recent uptick in methane emissions have come from wetlands in the Arctic. 

“When you warm up the wetlands in the Arctic, they just pour methane out. As far as we can see, during the summer the bulk of the emissions are coming from the wetlands in the summer, and gas leaks in the winter,” he said. 

From 1990 through 2011, the Environmental Protection Agency says the United States’ methane emissions fell, but worldwide methane emissions are still way up, and Nisbet says the natural gas boom could quickly make the US’s emissions a problem again. 

“Fracking, if it’s well controlled, it can displace coal and shouldn’t cause a lot of emissions,” Nisbet said. “But if you just frack like crazy and don’t worry about losing the gas, you put a lot of methane in the air. Each site right now is different.”

In Utah, up to 12 percent of all gas that’s fracked is believed to be lost to the atmosphere, but similar programs in Colorado are cleaner. 

Nisbet says that the uptick in methane could be part of a cycle, and it’s “too early to call it global warming for sure,” but that we could be entering dangerous territory. 

“Methane makes methane, that’s what we’re seeing. You have a feedback loop where methane heats things up and then we get more wetland emissions,” he said. 

The answer, he says, is better information from around the world that will let us know where we need to improve. 

“More data are needed to resolve the divergence between top-down and bottom-up estimates, but the measurement network for methane concentration and isotopes is very thing,” he writes. “Somewhere, perhaps in the tropics or East Asia, unwelcome methane surprises may lurk, but watchers are few.”