WASHINGTON, Thu Sep 27,(bdnews24.com/Reuters) - The world's biggest greenhouse gas polluters -- including the United States and China -- sent envoys to the US State Department on Thursday for discussions on climate change and what to do about it. The two-day meeting was called by President George W Bush, whose administration has been criticized for its refusal to adopt mandatory limits for climate-warming emissions. The White House favors "aspirational" targets. By most counts, the United States is the No. 1 emitter of greenhouse gases, notably carbon dioxide produced by coal-fired power plants and petroleum-fueled vehicles. But at least one study this year indicated that fast-developing China is now in the lead. Other participants are the European Union, France, Germany, Italy, the United Kingdom, Japan, Canada, India, Brazil, South Korea, Mexico, Russia, Australia, Indonesia and South Africa. This gathering of major economies follows a high-level United Nations meeting on Monday that drew more than 80 heads of state and government to focus on the problem of global warming. At its conclusion, Secretary-General Ban Ki-moon said he saw a "major political commitment" to seek a global solution to the problem at future U.N. discussions in December in Bali, Indonesia. At the United Nations and in Washington before the State Department meeting, envoys and lawmakers called on the United States to take a leading role. "US leadership in the area of climate change is essential, not only because it is a big emitter of greenhouse gases, but because the US is on the cutting edge of developing technological solutions and bringing them to the global market," said special UN climate envoys Gro Harlem Brundtland, Ricardo Lagos Escobar and Han Seung-soo at a Capitol Hill briefing. A letter to Bush from members of Congress, led by Massachusetts Democrat Ed Markey, who chairs the House of Representatives global warming committee, urged mandatory curbs on carbon dioxide emissions: "We need actual reductions in global warming pollution, not aspirational goals." "What would really galvanize the international efforts on climate would be a set of policies in the United States to put the United States on a fast track to building a low carbon economy," John Ashton, Britain's climate envoy, said in a telephone interview. "We now need to stop talking about talking and start deciding about doing." The Washington talks are not formal climate negotiations, but rather an airing of views on greenhouse gases, energy security, technology development and commercialization, financing -- and a daylong closed-door session on "process and principles for setting a long-term goal" to cut the human-caused emissions that spur climate change. Bush's proposal would come up with "aspirational goals" to limit emissions by the end of 2008, shortly before his administration leaves office. The Bali meeting in December is meant to begin figuring out a way to curb emissions after 2012, when the Kyoto Protocol expires. The Kyoto plan sets out mandatory targets for reducing greenhouse emissions, but the United States has rejected it as unfairly exempting fast-growing economies like China and India.