Now this is a funny headline: "Cow farts can now be regulated in California."

But it’s also a tad misleading. These news stories really ought to emphasize cow belches. Belches are the big global warming problem! Cow farts are secondary. C’mon, people.

Okay, let’s explain. Over the past few weeks, California has been passing a slew of ambitious global warming policies. That included SB 32, which mandates a 40 percent cut in overall greenhouse gases below 1990 levels by 2030. (That’s, uh, pretty drastic!)

As part of that barrage, California’s legislature passed SB 1383, which requires the state Air Resources Board to tackle some of the other climate pollutants that don’t get as much attention as carbon dioxide. That includes greenhouse gases like methane and hydrofluorocarbons, as well as black carbon.

So that’s where the cows come in. Methane is a particularly potent greenhouse gas, some 34 times as effective as carbon dioxide at trapping heat over a 100-year period. Methane accounts for 11 percent of total US climate pollution. And it comes from a bunch of different sources, including natural gas leaks, landfills, and livestock — the last through decomposing manure and a process called "enteric fermentation."

Oh yes, "enteric fermentation." Basically, cows evolved to eat grass. Grass is tough to digest (just try it), so cows have specialized four-chamber stomachs that process the food, regurgitate it back up into cud, and then re-digest it. Those stomachs also have various microbes, which break down the food and release CH4, or methane. Most of it comes through burping, a bit through farting.

It all adds up. California has a lot of dairy cows, and all that belching and farting and decomposing poop accounts for 5 percent of the state’s total greenhouse gas output. If you want radical emissions cuts, you gotta go for the belches.

The good news is that there actually are ways to reduce methane. Altering cow diets is the most promising technique at the moment. In some studies, researchers have fed cows things like infused flaxseed and reduced methane emissions up to 30 percent. The catch is that milk production can go down with some of these diets, and it’s not clear that the reductions are always permanent — the stomach microbes may eventually readjust. So more tinkering is needed.

Alternatively, some companies try to capture the methane, as Bloomberg’s Jason Strongin details here. Cargill is putting cow poop in giant domed lagoons to trap the biogas and use it for energy. Argentina, meanwhile, is experimenting with cow backpacks that capture the methane. Let’s go to the tape:

Better breeding might help, too. Scientists have noticed that different cows can emit wildly varying amounts of methane — by a factor of two or three. If this is influenced by genetics, it might be possible to select and breed only low-emitting cows. Still, figuring out the interplay between genetics, microbiology, and diet is tough, and there’s still a lot for researchers to untangle. Because cows have both a stomach and a rumen, "their digestive system is far more complex and hard to understand than ours," says Phil Garnsworthy of the University of Nottingham.

In any case, the new California bill will direct the state Air Resources Board and Department of Food and Agriculture to ruminate on all these methods and figure out which ones are most viable and cost-effective, in consultation with the dairy and livestock industries. Regulation will go into effect no later than 2018, with the aim of cutting methane pollution 40 percent by 2030.

There’s no guarantee any of this will be easy. Even simple tasks like measuring methane from hundreds of thousands of cows can be tricky. And, because livestock management can differ from place to place, a diet that works on one farm may not work as well on another. Meanwhile, not all farmers are necessarily near suitable infrastructure to sell biogas for energy even if they can trap it. So there’s a lot to hash out.

That said, cows are a big enough source of greenhouse gases that we’re going to have to figure this out at some point. Note that a recent study in Nature Climate Change found that high methane emissions may make it extremely difficult for the United States to meet its 2025 climate goals. California’s at least trying to make headway, burp by grassy burp.

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