Opposes mandatory controls on such gases as carbon dioxide and methane, saying any caps would hurt economy and instead favours voluntary means. In 2001, he rejected the UN's Kyoto Protocol, saying it would hurt the economy and wrongly exempted developing nations.

Bush calls for a reduction in greenhouse gas intensity -- the tonnage of emissions for every dollar of economic output -- by 18 percent in the decade to 2012. The United States spends more than other countries on developing new technologies such as hydrogen fuel and "clean coal". The administration is expected to push at Montreal talks for a multinational voluntary plan to sequester greenhouse gases underground.

MARKETS

Chicago Climate Exchange (CCX). Only major US exchange to trade greenhouse gases. Does not advocate mandatory caps. CCX has traded a total of 3.3 million tonnes of greenhouse gas since 2003, far less than the amount traded on the European Union's emissions trading scheme that opened this year.

US SENATE

In 1997, the US Senate voted 95-0 to reject Kyoto if it did not apply to developing nations and would damage the economy. Since then, interest has grown in capping emissions.

GOVERNORS

The Regional Greenhouse Gas Initiative (RGGI). Led by New York Gov. George Pataki, a Republican, nine states in the US Northeast have joined together with the goal of limiting greenhouse gas emissions. Would cut power plant emissions of global warming gases by 10 percent by 2020.

Three states in the West -- California, Washington and Oregon -- are hoping to forge a similar agreement.

Calif. Gov. Arnold Schwarzenegger, a Republican, has backed a proposal to limit carbon dioxide from cars. In November, New York state's Environmental Board adopted similar rules.

MAYORS

US Mayors Climate Protection Agreement. Signed by 180 mayors, including those in New York, Los Angeles and Chicago who represent 40 million US citizens. Signatories strive to meet or beat Kyoto targets in their cities and to urge their state and federal government to enact similar policies.

INVESTORS

Investors have filed shareholder proposals on global warming and renewable energy at publicly traded US companies for 16 years. Investor groups argue that excessive greenhouse gas emissions could leave companies liable to lawsuits.

COMPANIES

US companies including Dupont Co., American Electric Power Co. and Cinergy acknowledge that mandatory limits on carbon are inevitable and have set voluntary caps on greenhouse gases.