President George W. Bush pulled the United States out of the Kyoto Protocol on global warming in 2001, citing economic risks, but cities and states have since launched independent efforts to curb emissions and bypass the federal stand.

The most populous US state, California passed last year the first significant law in the United States to curb emissions of greenhouse gases, a move Europeans hope will pre-empt national US action.

"We're looking to be a model for the United States, which is also what the Europeans are hoping," said Linda Adams, secretary of the California Environmental Protection Agency, after meeting EU and European state officials on a fact-finding trip.

"There's a sense of urgency in Europe."

The world's twelth biggest carbon emitter, California has approved a state-level emissions cap in a possible model for a regional initiative including four other western states.

The US Supreme Court ruled on Monday that existing law allows regulators to slow emissions of greenhouse gases, potentially giving such regional moves fresh impetus.

"The supreme court ruling allows states to flex their muscles, so you'll see more initiatives," Adams said.

The court ruling could also unblock California's legal battle with automakers to introduce from 2009 a standard to cut auto emissions by 30 percent, and secure the state the necessary federal rubber stamp, Adams said.

Global warming is seen threatening California's people, forests and water supplies. More than a hundred people and thousands of dairy cattle died of heat stress in the state last summmer, Adams said.

CARBON MARKET

Carbon markets are much favoured by business as a way to tackle climate change because they can be used to make money. At present the global hub is an EU scheme.

Such markets give businesses a certain quota of emissions permits. If companies clean up and undercut their cap they can sell the surplus permits.

Advocates see a globally linked-up market as the ideal, cutting the cost of combating climate change by allowing industry to shop around for the world's cheapest permits.

California has agreed to limit its greenhouse gas emissions to 1990 levels by 2020, partly through a carbon market which it launches in 2012.

The fine print is still to be decided but the market would likely cover high-polluting industry including power generators, oil and gas, cement makers and landfill sites, Adams said.

The California scheme could link to a mooted market in eastern US states, called the Regional Greenhouse Gas Initiative, although RGGI covers fewer sectors and starts sooner.

It could also link to the European market, and to carbon trade between rich and poor nations under the Kyoto Protocol, through a currency of emissions offsets called Certified Emissions Reductions (CERs).

"We could set out rules to make an offset acceptable if it follows these (CER) standards," Adams said.