That's according to The New York Times, which acquired a draft copy of the report by scientists from 13 federal agencies.
The report says extreme heat waves have become more common and extreme cold waves less common since the 1980s.
It says emissions of greenhouse gases will affect the degree to which global temperatures continue to rise - a claim President Donald Trump and some members of his cabinet have disputed.
One scientist cited anonymously by the Times says he and other researchers are worried that the Trump administration, which must approve the report's release, will suppress it.
MORE SCIENCE: How will U.S. withdrawal from Paris accord impact global climate?
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