Climate report ominous, but what will Trump think?

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 climatechange 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 Donald Trump and members of his Cabinet who say that the human contribution to climate change is uncertain, and the ability to predict the effects are 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 are concerned about its fate.

The report concludes that if the current trajectory of emitting fossil fuels holds steady, the world will have to accept an additional 0.50 degrees Fahrenheit (0.30 degrees Celsius) of warming over this century. A small difference in global temperatures can make a big difference in the climate: The difference between a 1.5degree Celsius and a 2-degree Celsius rise in global average temperatures, for example, could mean longer-lasting heat waves, more intense rainstorms and the faster disintegration of coral reefs.

In the United States, the report finds with ‘‘very high’’ confidence 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 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.

‘‘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,” said Michael Oppenheimer, a professor of geoscience and international affairs at Princeton University who was not involved in the study.

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.