They also play down the benefits of reducing emissions, disputing recommendations by European governments that greenhouse gases be capped at around 445 parts per million in the air. The current level of greenhouse gases is about 430 ppm.

The Intergovernmental Panel on Climate Change, a United Nations network of 2,000 scientists, drew up the plan. Governments have spent the last few weeks reviewing the proposals and are meeting with the scientists this week to work out their differences.

The U.S. and Chinese comments, in documents reviewed by The Associated Press, are a precursor to what delegates expect will be a fight for much of the week to preserve the key conclusions of the draft IPCC report, which says emissions can be cut below current levels if the world shifts away from carbon-heavy fuels like coal, invests in energy efficiency and reforms the agriculture sector.

The plan must be unanimously approved by the 120-plus governments that participate, and all changes must be approved by the scientists. A spokesman for the U.S. delegation declined to discuss the American position until the final report Friday.

Two previous IPCC reports this year said unabated greenhouse gas emissions could drive global temperatures up as much as 11 degrees by 2100. Even a rise of 3.6 degrees could subject up to 2 billion people to water shortages by 2050 and threaten extinction for 20 percent to 30 percent of the world's species, the U.N. panel of scientists said.

Scientists have said global warming could increase the number of hungry in the world in 2080 by between 140 million and 1 billion by contributing to widespread droughts and flooding. Diseases like malaria, diarrhea and dengue fever could spread as temperatures rise and weather becomes increasing erratic, affecting the poorest of the world's poor.

The third report says the world must quickly embrace a basket of technological options — already available and being developed — just to keep the temperature rise to 3.6 degrees.

But the United States wants to take a longer-term approach with mitigation measures, a position that will likely anger island nations and other developing countries already feeling the effects of climate change.

The U.S. wants language inserted into the report that says the cost of available current technologies to reduce emissions "could be unacceptably high" and calls for putting greater emphasis on "advanced technologies." Many of the latter, like carbon sequestration, are aimed at extending the use of coal.

"Mitigation efforts over the next two to three decades can reduce the rate of growth of greenhouse gas concentrations," the U.S. said. "However, development and commercialization of advanced technology and implementation of advanced practices will have a large bearing on long-term greenhouse gas concentrations."

The United States and China also dispute the economics in the report, which concludes that achieving the 445-534 ppm range might cost under 3 percent of global gross domestic product over two decades.

The report's conclusion compares favorably to global economic growth that has averaged almost 3 percent annually since 2000. The damage from unabated climate change, meanwhile, might eventually cost the global economy between 5 percent and 20 percent of GDP every year, according to a British government report last year.

The United States also raises concern that switching away from coal would be "bad for energy security," questions the benefits of fuel efficient cars and attempts to minimize the economic benefits of mitigation including job creation.

"The co-benefits of balance of trade improvement, wealth creation and employment" are not substantiated," it says. "The supposed benefits are, in most cases, merely a transfer between regions and sectors rather than a general acceleration in global growth. The mitigation policies will have costs and are unlikely to result in a win-win."

Rajendra Pachauri, chairman of the climate change panel, wouldn't address the U.S. comments directly. But he said "every country" would have a chance to express its views and "ultimately its a balanced assessment of the science that will prevail."