The United States and China want to water down a proposed plan for fighting climate change, arguing that action to reduce greenhouse gases will be more costly and time-consuming than scientists claim, documents show.

The U.S. and China, in papers reviewed by The Associated Press, claim that a proposed European cap on greenhouse gas levels is too low and reaching the target would be too expensive.

The Intergovernmental Panel on Climate Change, a United Nations network of 2,000 scientists, has issued two reports on the impacts of global warming. The plan that the U.S. and China want to weaken lays out ways of dealing with those impacts.

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Governments have spent the last few weeks reviewing the proposals and are meeting with scientists this week to work out their differences before a formal document is issued Friday.

Delegates expect a fight to preserve the key conclusions of the draft, which says emissions can be cut below current levels if the world takes such steps as reducing use of carbon-heavy fuels like coal, investing in energy efficiency and changing farm methods.

The report must be unanimously approved by the 120-plus governments that participate, and all changes must be approved by the scientists.

Harlan Watson, the head of the American delegation, said in an e-mail that the U.S. goal is to produce a report that is "useful to the policy community" and is "supported by scientific and economic data."

The 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 draft of 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. and China challenge the economic benefits of reducing emissions, disputing recommendations by European governments that greenhouse gases be kept from going above 445 parts per million in the air. The current level of greenhouse gases is about 430 ppm.

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 which are aimed at extending the use of coal.

The United States and China dispute the reports conclusion that reining in greenhouse gas emissions might cost under 3 percent of global gross domestic product over two decades. In its comment, China said the number of studies supporting that forecast is "relatively small."

The United States also questions predictions of economic gains from efforts to reduce emissions, such as creating jobs from new technologies.

"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."

While joining the U.S. in questioning the affordability of taking action, China also wants more to be required of countries with high per-capita greenhouse gas emissions, such as the United States.

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."

"The science certainly provides a lot of compelling reasons for action," Pachauri said. "But what action and when is what the government will have to decide."