The legislation California enacted last month to seize for itself a leading role in the fight against global warming is only the beginning of what will probably be five years of intense, behind-the-scenes battles over just how to reduce greenhouse gases to the level emitted in 1990, when California's population and its economy were much smaller than they are today.

AB 32 was titled the Global Warming Solutions Act of 2006. But the bill does little more than establish the goal of reducing the state's greenhouse gas emissions by 25 percent below levels now projected for 2020. That's about 174 million metric tons of carbon dioxide, which, by volume, is equivalent to filling 64 Empire State Buildings from the lobby to the tower above the observation deck.

Most of the heavy lifting will be done by the Air Resources Board, an 11-member panel that includes 10 citizen regulators and one full-time chairman appointed by the governor. The legislation grants the board extraordinary powers to set policies, draw up regulations, lead the enforcement effort and levy fees to finance it all and fines to punish violators.

What will it take to achieve the benchmark? Consider that California could take every one of its 14 million passenger cars off the road, and still be less than halfway toward its goal. Shutting down 100 state-of-the-art, natural-gas-fired power plants still wouldn't get us there. Closing the entire cement industry, although it is a major source of greenhouse gases, wouldn't finish the job.

In fact, none of those draconian steps will be taken -- but regulators hope many smaller steps together can get California to its ambitious goal without ruining the state's economy.

The process will begin next summer, when the air board is due to publish a list of the easiest steps the state and its industries could take to reduce emissions -- the low-hanging fruit ready for picking immediately. These might include measures to reduce idling of diesel-fueled trucks and of ships docked in port, new regulations on auto air conditioning and other refrigeration units, and restrictions on emissions from manure piled up at Central Valley farms.

By January 2008, the board is supposed to adopt its formal estimate of the 1990 levels to which California must reduce its emissions and a system for requiring companies to monitor and report their emissions to the government.

The board's first comprehensive plan for how the state will meet that goal is due by January 2009. That document is supposed to spell out how much of the reduction will come from which industries. It will also describe how much of the reduction will be achieved through direct regulation of business practices and how much through a market in which companies can purchase the right to pollute from other firms that have reduced their emissions by more than the required amount.

By January 2011, the board is scheduled to adopt the regulations, and those rules will take effect one year later. The board will also be free to levy and collect fees to finance the project and assess fines to punish companies that fail to comply.

The legislation does not limit the air board's discretion in deciding which industries and companies to target. But officials expect that, at least initially, most of the attention will be focused on five major sources of greenhouse gases: electricity generation, oil and gas extraction, oil and gas refineries, cement production, and landfills.

Chuck Shulach, who is managing the greenhouse gas reduction program for the air board, said it is not likely that each individual industry will be expected to reduce its emissions to 1990s levels. Instead, the state as a whole will have to meet that standard, and the air board will divvy up the responsibility according to the law's edict to force each industry to achieve the ``maximum feasible and cost-effective'' level of reduction.

These are revolutionary changes, breathtaking in their scope. The technical, legal and regulatory grind to come will represent one of the greatest social engineering projects ever undertaken by state government. It will deserve close scrutiny.