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In the parlance of climate change, the phenomenon is known as "leakage."

Last month, Northview Dairy in Ontario, Calif., sold nearly 3,000 cows to a farmer with properties in Kansas and Colorado. Northview dairy manager German Cisneros said the sale was the result of a combination of increasing regulations, high prices for cows and a great offer from a company to turn the land into housing.

It makes perfect sense from a business perspective. But those former California cows are now residents of states with different air-quality laws. And in the global effort to combat climate change by cleaning up dairy farming, that matters.

When Northview Dairy set up shop in the 1990s, there were an estimated 500 dairy farms housing some 400,000 cows in Chino and south Ontario, making the region one of the most concentrated places for milk production on the planet. Today, Cisneros said there are just 22 dairies left, surrounded by massive warehouse buildings and tract home communities with names like "Amberhill Farms."

Many of the once-local cows have gone north to places like Bakersfield and the San Joaquin Valley, where land is cheaper and urban creep less intense. But, as with Northview's herd, thousands of others have been shipped across state lines to dairies that don't have to worry as much about rising costs, worsening water shortages and rigorous regulations around everything from animal welfare to air quality.

California has set the most ambitious goals in the nation for reducing methane emissions. These greenhouse gases don't stick around in the atmosphere nearly as long as carbon dioxide but are much more potent, which means they contribute significantly to global warming. And since dairies are responsible for more than half of the state's methane emissions, legislators in 2016 set a goal to reduce emissions from farms by at least 40%, or some 9 million metric tons, by 2030.

Since passage of that law, the state's 1,200 dairies have made huge strides in reducing methane emissions. A report this spring by the California Air Resources Board estimated state farms are nearly halfway to the goal.

But while half of those reductions have come from dairies changing the ways they process cow manure, the other half has come because California is simply losing cows. And when cows are moved, global methane emissions don't actually drop. They just shift, or "leak," into another state, where lighter regulations mean the greenhouse problems likely will get worse.

Cow exodus

Many industry advocates fear that such leakage could get worse in the next couple of years.

So far, California has relied on incentives and outreach programs to get dairy farmers to help reduce methane emissions. But under the 2016 law, the state could shift to a more punitive approach as soon as Jan. 1, 2024.

If that happens, Michael Boccadoro, executive director of Dairy Cares, a nonprofit that promotes sustainability for the industry, said he fears more of the state's remaining 1.7 million cows will head east — even as global demand for milk products rises.

"California doesn't want to be accused of adopting policies that result in the export and increase of methane emissions," Boccadoro said.

Solutions are working

When it comes to methane emissions from dairies, the problem originates from both ends of the cow.

A combination of what most dairy cows eat and how their digestive systems work leads to concentrated methane being released with each enteric emission — that's polite farm talk for a burp. And when cow manure decomposes without oxygen, just as with all organic material, it releases methane along the way.

Aside from having fewer cows, the most proven way to reduce methane at dairy farms is to add an anaerobic digester system to deal with manure. Roofs are placed over manure lagoons to capture methane and other gases as they're released. Those gases are then converted into renewable biogas, which can be used to power natural gas-equipped vehicles, injected into existing natural gas pipelines or used to produce electricity.

Already, more than 120 digesters are up and running at California dairy farms, and Boccadoro said at least another 120 are in some stage of development. Those systems are reducing methane emission from manure lagoons by 80%.

Digesters aren't cheap, though. It costs about $6 million to add one at a 2,000-cow farm.

Cow burps account for an estimated 30% of California's methane emissions. The industry is waiting on government approval for a variety of products that, when added to cow feed, have shown promise at substantially reducing the amount of methane in each belch.

Lakeview farmer Michael Oosten, 36, whose family's dairy has been in Southern California since the end of World War II, said he's particularly encouraged by early research showing some of these additives can also help improve cow nutrition and therefore milk production, which would mean more revenue to offset the cost of the products.

Farmers like Oosten see these methane-reducing steps as part of larger sustainability plans.

Like most of the industry in California, for example, he already gets up to 50% of his cow feed through byproducts from other industries, such as stale bread from bakeries and pulp from local citrus farms. This reduces resources needed to grow feed crops and it keeps those byproducts out of landfills, where they'd generate their own methane as they decomposed.

Oosten also added solar panels to his property, and he just ordered his first electric tractor.

Such practices, if widely used, could help the state's dairy industry reach climate neutrality by 2027, predicts Denise Mullinax, executive director of the California Dairy Research Foundation, who said her organization reached that conclusion as part of a study it completed with a researcher at UC Davis.