BUENOS AIRES, Argentina — International experts, searching for ways to break a deadlock with the United States over climate change, consulted on an array of ideas Monday to lure that No. 1 polluter into a joint effort to control "greenhouse gases," along with such second-rank emitters as China and India.

A Chinese negotiator said he believed Washington might accept a concept he favored -- "the bottom-up approach," whereby individual nations decide what steps they can take to rein in carbon dioxide and other emissions.

That would reverse the "top-down" approach of the 1997 Kyoto Protocol, which the Bush administration rejects and which sets mandatory targets for dozens of nations to cut back by 2012 on the gases blamed for global warming. Environmentalists said, however, that the "bottom-up" approach may accomplish little.

An annual U.N. conference on climate change was midway through its two weeks here as representatives of almost 200 nations refined details of Kyoto in formal sessions, while informally debating how to control emissions beyond 2012.

Official talks on that future framework are expected next year. But since July the Pew Center on Global Climate Change, a private Washington research group, has brought together policy-makers and experts from the United States and 14 other nations for closed discussions on the next steps to slow global warming.

At a briefing Monday, the Pew Center's Eliot Diringer said the participants thus far have agreed that "a future climate approach should aim, No. 1, to engage major emitters."

The United States is the biggest, emitting 21 percent of the world's greenhouse gases in 2000, according to a report issued Monday by the Pew Center and the World Resources Institute of Washington. The No. 2 emitter is China, accounting for 15 percent of the gases, more than the entire 25-nation European Union's 14 percent.

The Kyoto pact seeks to control six gases that trap heat that otherwise would escape the atmosphere. Carbon dioxide, the most common, is a product of coal- and oil-burning power plants, automobile exhaust and other fossil fuel-burning sources.

A scientific consensus, endorsed by a U.N.-sponsored network of climate experts, blames much of the Earth's temperature rise of recent decades on these emissions, and warns it will lead to damaging climate disruptions.

Under the Kyoto pact, which takes effect Feb. 16, governments of 30 richer nations are to set quotas for their industries' emissions to meet specified national targets. But China, India and other poorer nations were exempted from Kyoto's short-term targets. President Bush renounced Kyoto in 2001, saying it would damage the U.S. economy and complaining of the exemptions.

"The rejection by the United States really set off the search for better ways of doing things," Michael Zambia Cutajar, one of the Pew conferees, said Monday.

"What seems to be taking shape is a series of feasible options that respond to different economic and political circumstances," said Cutajar, a Maltese diplomat who helped oversee the Kyoto negotiations.

The Pew experts, whose formal recommendations are expected next year, have focused on 15 ideas that might produce a "variable geometry" of methods for controlling emissions past 2012. The University of Georgia's Dan Bodansky said methods might vary country to country.

The methods could include reduction targets indexed to national GDPs, allowing emissions growth commensurate with economic growth, he said, along with targets designed solely for power plants or other individual economic sectors.

He said some have even proposed purely financial commitments -- pledges by rich countries not to targets, but to financial commitments to pay for reductions elsewhere.

Chinese climate negotiator Gao Feng, a Pew participant, endorsed this idea of a "menu" of options and said he favored the "bottom-up approach," defined by a Pew paper as each country determining for itself "what might be technically, economically, socially and politically acceptable."

Some might make emission reductions mandatory, some voluntary, Gao said, but "we'd allow countries to take the most appropriate choice for themselves."

The Bush administration says it's "premature" to discuss post-2012 arrangements. But Gao said he has met informally with U.S. officials, and "I think that (`bottom-up') might be the only possible way to engage the United States."

Bill Hare, a climate expert for the environmental group Greenpeace, was dismissive of such a voluntary approach. "Bottom-up is a euphemism for not doing much at all beyond what would normally happen," he said.

Source: Associated Press