A major draft federal report concludes that climate change is already affecting U.S. residents through heat waves, droughts and other changes, and warns that temperatures could increase as much as 10 degrees Fahrenheit if global carbon emissions keep soaring.



The third National Climate Assessment, released Friday, said there’s “unambiguous evidence” that earth is warming, and that climate change over the past 50 years is driven primarily by human activity, especially from burning fossil fuels.



“Certain types of weather events have become more frequent and/or intense, including heat waves, heavy downpours, and, in some regions, floods and droughts. Sea level is rising, oceans are becoming more acidic, and glaciers and arctic sea ice are melting,” states the draft report developed by a federal advisory panel.



“These changes are part of the pattern of global climate change, which is primarily driven by human activity,” adds the draft report, released through U.S. Global Change Research Program.

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The report tallies the wide-ranging effects of climate change, such as water supplies stressed by declining runoff and increased risk of heat stress and waterborne disease, and notes that U.S. infrastructure is already being harmed by sea-level rise, storm surges and heavy downpours.



It also tallies regional effects of climate change in the U.S.



Environmentalists quickly seized on the report, which follows a separate federal announcement that 2012 was the hottest year on record in the lower 48 states, to call for more aggressive steps to drive down emissions.



“This could help restart a national conversation about climate change,” said Todd Sanford, a scientist with the Union of Concerned Scientists. “It gives us a road map for climate change. And the road is much bumpier if we continue along a higher emissions pathway.”



Carol Browner, President Obama’s former climate czar, said the U.S. has made progress in reducing emissions but more action is needed immediately.



“We can start with strict carbon pollution standards for power plants and we must significantly expand investments in community resiliency to protect people and the economy from the gathering storms — and floods, droughts, wildfires, and heat waves,” said Browner, who is now a senior fellow with the liberal Center for American Progress.



The report finds that U.S. temperatures will continue rising 2 degrees F to 4 degrees F in most areas in the coming decades, and calls for effort to increase resilience to changes that cannot be avoided.



But it’s unclear how high temperatures will climb. The report provides a range of 3 degrees F to 5 degrees F by century's end if global emissions are reduced sharply after 2050, and up to 10 degrees F if they’re not.



Average U.S. temperatures have risen roughly 1.5 degrees F since 1895, and more than 80 percent of that increase has occurred since 1980, the report concludes.



The report is just the latest broad study or statement by a scientific body to conclude there’s overwhelming evidence that global warming is under way and that human activities are a major cause.



For instance, the National Research Council, in a 2011 report, noted that climate change is “very likely caused primarily” by human-induced greenhouse gas emissions.

However, a substantial number of Republicans dispute the conclusion that human activities are the primary driver of climate change.



Rep. Lamar Smith (R-Texas), chairman of the House Science, Space and Technology Committee, said in a statement Friday that he plans to vet climate science in the new Congress.



“I believe climate change is due to a combination of factors, including natural cycles, sun spots, and human activity. But scientists still don’t know for certain how much each of these factors contributes to the overall climate change that the Earth is experiencing,” he said in a statement Friday.



“It is the role of the Science Committee to create a forum for discussion so Congress and the American people can hear from experts and draw reasoned conclusions,” he said. The panel will have a hearing on the environment in coming weeks, according to committee aides.



While climate advocates are pouncing on the report, it’s unlikely to fundamentally change the politics of climate change on Capitol Hill, where bills to cap emissions or impose carbon taxes are moribund.



However, green activists are pressing for stronger executive actions, such as Environmental Protection Agency carbon emissions standards for existing power plants.



The broad new federal assessment was released in draft form Friday by the National Climate Assessment and Development and Advisory Committee, which is comprised of experts from academia, various industries and elsewhere.



The National Research Council will review the draft, which is also open for public comment.



The report was crafted under the Global Change Research Act of 1990, which requires wide-ranging climate reports to the president and Congress.

This post was updated at 5:34 p.m. on Jan. 12

