A special scientist panel, meanwhile, started closed-door talks to complete a report set to be released later this week that warns global warming will have dramatic repercussions for humankind.
EU Environment Commissioner Stavros Dimas lashed out at Washington and Australia for their reluctance so far to join the 27-nation EU and other rich countries in fighting climate change. The United States has refused to endorse the 1997 Kyoto Protocol.
Dimas said the U.S. should end its "negative attitude" toward international negotiations on a new climate change pact to reduce emissions, which could start in December.
"We expect from the United States to cooperate closer," Dimas said. "It is absolutely necessary that they move because, otherwise other countries, especially the less developing countries, do not have any reason to move."
Dimas also criticized Australia for not applying Kyoto, which requires 35 industrial nations to cut greenhouses gases.
"I cannot comprehend why Australia has not ratified the Kyoto Protocol," he said, adding that 80 percent of public opinion in Australia supported Kyoto.
Australia is ranked as the world's worst greenhouse gas emitter per capita, largely due to its heavy reliance on coal-fired power stations.
But Prime Minister John Howard refused to ratify Kyoto, arguing that to do so could cost Australian jobs because neither China nor India were held to carbon pollution reduction targets.
Belgian Prime Minister Guy Verhofstadt said all nations had to do their bit to save the planet.
"I call on the politicians of the other industrial states, especially the United States, India and China, not only to sign the current Kyoto Protocol, but also to start with new, necessary negotiations," he said.
The five-day meeting of the Intergovernmental Panel on Climate Change, or IPCC _ a network of more than 2,000 scientists _ will finalize a report on how warming will affect the globe and whether humans can do anything about it.
"From a human point of view this is absolutely critical," the U.N. panel's chairman, climatologist Rajendra Pachauri of India, said. "We need to understand what climate change means for us in our own lives and how its going to affect both natural and social systems."
The meeting is expected to endorse a draft U.N. study that paints a bleak picture of increasing poverty, paucity of drinking water, melting glaciers and polar ice caps, and a host of vanishing species by mid-century unless emissions of carbon dioxide and other heat-trapping gases are curbed.
The report, drafted by the world's top climate change experts, will be presented at a Group of Eight leaders summit in June in Germany, which the EU will use to put more pressure on U.S. President George W. Bush to sign up to international talks to cut emissions.
Dimas said the EU's recent pledge to cut carbon emissions by at least 20 percent from 1990 levels by 2020 was partly due to the IPCC's earlier report last month. The EU said it could go to 30 percent if other countries join.
The Bush administration has argued the Kyoto Protocol would hurt the U.S. economy and also objects that the protocol exempts China and India from emission reductions.
The meeting could also focus on predictions of how many people will be at high risk from changing ecosystems, and whether specific weather events like Hurricane Katrina should be attributed to global warming.
Martin Hiller, climate change expert at environmental group WWF, said the conference was "crucial" to influence political leaders and to change government policy.
"We want to see what needs to be done to protect vulnerable communities. People who live in areas which are already affected by climate change, through drought, through flooding, through problems with their drinking water supply," Hiller said. "We need to see what can be done to protect them now."
About 285 delegates from 124 countries are attending, along with more than 50 of the scientists who compiled the report and dozens of observers from nongovernment, mostly environmental, organizations.
A draft of the IPCC's summary has been obtained by The Associated Press, but policy makers will go over the document this week before unveiling the final text Friday.
It is the second of four reports by the IPCC. The first, issued in February, updated the science of climate change, concluding with near certainty that global warming is caused by human behavior.
This week's draft was six years in the making. Since the IPCC's 2001 assessment, knowledge about climate change has become more precise.
"Many natural systems on all continents and in some oceans are being affected by regional climate changes, particularly temperature increases," reads the draft.
Scientists and environmental groups have warned that storms, floods and droughts have increased over past years due to climate change.
The report will offer stark warnings for the future.
A follow-up report in May is to outline possible ways to slow the affects of global warming.