FRESNO, Calif. _ The battle against global warming may turn out to be a boon for an industry long targeted by environmentalists _ dairies.

In California's Central Valley, some dairy farmers have been so successful in reducing air pollution from animal waste that they're earning revenue from other industries that need help meeting their own emission goals.

Those transactions are tied to a controversial idea called "cap-and-trade," a system that lets companies meet air-pollution requirements by getting credit for reductions that other companies achieve.

Some critics on the conservative right, often skeptical that global warming is a real problem, call cap-and-trade a pointless and expensive government intervention. Some critics on the left say the practice allows industrial polluters to buy their way out of tighter emissions controls.

In California, however, both the state and federal governments are pushing cap-and-trade systems all the same, backed by supporters who say the practice creates a practical, market-driven tool to reduce emissions.

That's created a potential revenue source for California's struggling dairy industry _ and it could offer a glimpse of how the battle against global warming will be fought nationwide.

"Cap-and-trade does get a lot of people excited," said David Albers, the president of the 2,800-cow Vintage Dairy in western Fresno County.

For years, dairies have come under scrutiny because cow manure releases methane as it decomposes. Methane is among the greenhouse gases that are blamed for global warming.

Across California, however, some dairies have been able to reduce the emissions with methane digesters, which work by capturing gas for use as fuel instead of allowing it to be released.

Read the complete story at fresnobee.com