The Obama administration's top climate change scientists will unveil a report on Tuesday that details the impact of global warming on the United States and argues for fast action against it.

The report by the U.S. Global Climate Research Program is billed as a comprehensive scientific report on current and pending impacts of global climate change in the United States, and why it is important to act now, rather than later, to minimize those impacts.

Rather than a simple release on paper or online, the report is being released at a news conference by John Holdren, who heads President Barack Obama's Office of Science and Technology Policy, and Jane Lubchenco, who heads the National Oceanic and Atmospheric Administration, among others.

The report's conclusions are expected to be in line with the administration's support for a market-based cap and trade system to limit emissions of the climate-warming gas carbon dioxide, which is emitted by coal-fired power plants, fossil-fueled vehicles and other industrial and natural sources.

A bill to set up this kind of system is moving through the U.S. House of Representatives now, with approval by a key committee on May 22 and a possible vote by the full House by August. Democratic supporters say they want the bill to become law this year, but the outlook in the Senate is unclear.

While the report was not available Monday, it is expected to be similar to a draft version posted online in January.

Among the January draft's key findings:

-- climate change is already affecting water, energy, transportation, agriculture, ecosystems and health, differing from region to region and expected to grow if the climate changes as projected;

-- agriculture is one sector most able to adapt to climate change, but increased temperature, pests, diseases and weather extremes will challenge crops and livestock production;

-- threats to human health will increase, especially those related to heat stress, water-borne diseases, reduced air quality, extreme weather events and diseases transmitted by insects and rodents;

-- sea-level rise and storm surge place many U.S. coastal regions at increasing risk of erosion and flooding, especially along the Atlantic and Gulf coasts, Pacific islands and parts of Alaska; energy and transportation infrastructure in coastal cities is very likely to be adversely affected.

The White House hopes progress on U.S. cap and trade legislation will help efforts to craft a new international pact to curb climate change, culminating in a global meeting in Copenhagen in December.

(Editing by Eric Beech)

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