WASHINGTON — The average temperature in the United States has risen rapidly and drastically since 1980, and recent decades have been the warmest of the past 1,500 years, according to a sweeping federal climate change report awaiting approval by the Trump administration.
The draft report by scientists from 13 federal agencies, which has not yet been made public, concludes that Americans are feeling the effects of climate change right now.
It directly contradicts claims by President Trump and members of his Cabinet who say that the human contribution to climate change is uncertain and that the ability to predict the effects is limited.
“How much more the climate will change depends on future emissions and the sensitivity of the climate system to those emissions,” a draft of the report states.
A copy of it was obtained by The New York Times.
The report was completed this year and is part of the National Climate Assessment, which is congressionally mandated every four years.
The National Academy of Sciences has signed off on the draft and is awaiting permission from the Trump administration to release it.
One government scientist who worked on the report, and who spoke to The Times on the condition of anonymity, said he and others were concerned that it would be suppressed.
The report concludes that even if humans immediately stopped emitting greenhouse gases into the atmosphere, the world would still feel at least an additional 0.50 degrees Fahrenheit (0.30 degrees Celsius) of warming over this century compared with today.
A small difference in global temperatures can make a big difference in the climate: The difference between a rise in global temperatures of 1.5 degrees Celsius and one of 2 degrees Celsius, for example, could mean longer heat waves, more intense rainstorms and the faster disintegration of coral reefs.
Among the more significant of the study’s findings is that it is possible to attribute some extreme weather to climate change.
The field known as “attribution science” has advanced rapidly in response to increasing risks from climate change.
The report finds it “extremely likely” that more than half of the global mean temperature increase since 1951 can be linked to human influence.
In the United States, the report finds with “very high” confidence that the number and severity of cool nights has decreased, while the frequency and severity of warm days has increased since the 1960s.
Extreme cold waves, it says, are less common since the 1980s, while extreme heat waves are more common.
The study examines every corner of the United States and finds that all of it was touched by climate change.
It said the average annual rainfall across the country has increased by about 4 percent since the beginning of the 20th century. Parts of the West, Southwest and Southeast are drying up, while the Southern Plains and Midwest are getting wetter.
With a medium degree of confidence, the authors linked the contribution of human-caused warming to rising temperatures over the Western and Northern United States. It found no direct link in the Southeast.
The Environmental Protection Agency is one of 13 agencies that must approve the report by Aug. 13. The agency’s administrator, Scott Pruitt, has said he does not believe that carbon dioxide is a primary contributor to global warming.
“It’s a fraught situation,” said Michael Oppenheimer, a professor of geoscience and international affairs at Princeton University who was not involved in the study. “This is the first case in which an analysis of climate change of this scope has come up in the Trump administration, and scientists will be watching very carefully to see how they handle it.”
Scientists say they fear the Trump administration could change or suppress the report. But those who challenge scientific data on human-caused climate change say they are equally worried that the draft report, as well as the larger National Climate Assessment, will be publicly released.
“The National Climate Assessment seems to be on autopilot because there’s no political that has taken control of it,” said Myron Ebell, a senior fellow at the Competitive Enterprise Institute. He was referring to a lack of political direction from the Trump administration.
The government scientists wrote that surface, air, and ground temperatures in Alaska and the Arctic are warming at a frighteningly fast rate — twice as fast as the global average.
“It is very likely that the accelerated rate of Arctic warming will have a significant consequence for the United States due to accelerating land and sea ice melting that is driving changes in the ocean including sea level rise threatening our coastal communities,” the report says.
Human activity, it goes on to say, is a primary culprit.