What Bill Would Do, Who's Affected

Amid concern about global climate change, the state Legislature gave final approval Thursday to AB 32, a bill to combat global warming.

What would the bill do?

AB 32 requires California's Air Resources Board to develop a program to reduce the state's greenhouse gas emissions to 1990 levels by 2020, a cut of about 25% from today's levels. Reductions will be required starting in 2012.

What are greenhouse gases?

Greenhouse gases, which trap heat in the atmosphere, are identified in the bill as carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.

Where do they come from?

Globally, power plants and office buildings produce about two-thirds of greenhouse gas emissions, and cars and trucks produce much of the rest. In California, the percentage from mobile sources is slightly higher, both because we drive so much and because statewide energy efficiency standards exist for buildings but not vehicles.

What businesses would be affected?

Utility plants, oil and gas refineries, factories and cement kilns, among other major emitters of the gases.

How can the state reach 1990 levels?

Experts say emissions would have to be reduced by 174 million metric tons. The approaches for achieving those reductions could include mandatory limits on emissions from utilities, cement companies and other heavy industries; energy efficiency measures; and the establishment of a market-based emissions trading program.

What are the major challenges to meeting the goals?

The U.S. Environmental Protection Agency has declined to support a California tailpipe emissions-control law, which is being challenged in court by automakers. Moreover, the EPA has chosen not to classify greenhouse gas emissions as pollutants, a decision being challenged in court by the Sierra Club and several states.

If California were to meet its emission-reduction goal, what would the effect be on the state's climate?

Unless other states and nations follow suit, there would be little effect, according to Ken Caldeira, a climate scientist at the Carnegie Institution's department of global ecology at Stanford.

"While it's important for the United States and California to show leadership, the actual effect on California's climate of reducing the state's carbon dioxide emissions will be negligible," Caldeira said. "It would be an altruistic gift from California to the rest of the world."