Supporters of California's global warming law have raised more than $2 million so far to defend the landmark legislation in what's shaping up as an expensive November ballot battle.

Filings with the California secretary of state show that environmental groups and clean energy advocates were big givers to the campaign against Proposition 23, which would suspend AB 32 until the unemployment rate drops to 5.5 percent.

Donors included the Natural Resources Defense Council, which contributed $975,000, and the Green Tech Action Fund, which gave $500,000. Anne Earhart, a longtime backer of environmental causes and an heiress to the Getty family fortune, donated $250,000.

The fundraising effort rivals that of the California Jobs Initiative Committee, which is spearheading the effort to roll back California's climate change law.

Backed by Texas oil companies Tesoro Corp. and Valero Energy Corp., the California Jobs Initiative has raised about $3.1 million for the Proposition 23.

It could just be the start of the spending.

"I expect this to be the most expensive initiative on the November ballot," said Robert Stern, an expert on initiatives and president of the Center for Governmental Studies in Los Angeles.

Signed by Gov. Arnold Schwarzenegger in 2006, AB 32 aims to reduce greenhouse gas emissions statewide to 1990 levels by the end of the decade.

Opponents of the law have argued that the state will lose more than 1 million jobs and and productivity will decline by billions of dollars as the emissions reductions are enforced.

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