Democrats questioned why the state planned to spend millions of dollars on mechanisms that have yet be evaluated or clearly defined.

“A lot of the language we’re using here is very fuzzy,” said Assemblywoman Loni Hancock, D-Berkeley, chair of the Assembly Natural Resources Committee. “I think we really need to develop something that all of the public understands.”

The committee held the Legislature’s first public hearing on how to implement the greenhouse gas reductions called for in the law, which was signed with great fanfare last year by Gov. Arnold Schwarzenegger.

It imposes the country’s first statewide cap on emissions of the heat-trapping gases that are blamed for global warming. The law requires California to reduce emissions by an estimated 25 percent by 2020 – an estimated 174 million metric tons.

The California Air Resources Board, which was charged with implementing the law, has begun hearings and workshops to sort out how much the state must reduce its emissions and what industries will be asked to do.

The board is considering a variety of strategies, including creating new regulations for fuels and creating a market that would allow companies to buy and sell credits to meet their obligations under the law, commonly referred to as Assembly Bill 32.

“This is a critical moment,” said Ira Ruskin, D-Redwood City. “Implementing AB32 is probably a task equally important as passing AB32. We have to set the right tone for the coming years.”

The law is one of the key ways California lawmakers are seeking to limit global climate change.

Scientists and experts in various state agencies predict climate change could diminish California’s water supply, stress farm land and forests, and alter the coast line as sea levels rise.