Washington — Directly contradicting President Donald Trump, a draft report produced by 13 federal agencies concludes that the United States is already feeling the negative impacts of climate change, with a stark increase in the frequency of heat waves, heavy rains and other extreme weather over the last four decades.

The preliminary report summarizes the current state of the science for the upcoming National Climate Assessment. Trump and his Cabinet have expressed public doubts that the warming is being primarily driven by man-made carbon pollution and will have serious consequences for Americans.

An early version of the report, a copy of which the Associated Press obtained, was distributed widely in December for review by leading scientists. The New York Times published a copy Monday.

The U.S. Global Change Research Program, which will edit and produce the final report, did not respond to phone and emails seeking comment on Tuesday.

The assessment has generally been released every four years under a federal initiative mandated by Congress in 1990. The current draft, targeted for release later this year, largely builds on the conclusions of the 2014 assessment released under the Obama administration.

The assessment said global temperatures will keep rising without steep reductions in the burning of fossil fuels, with increasingly negative impacts. Worldwide, 15 of the last 16 years have been the warmest on record. Tuesday, the National Oceanic and Atmospheric Administration said 2017 is on track to be the second warmest for the U.S.

The report calls the long-term evidence that global warming is being driven by human activities “unambiguous.”

“There are no alternative explanations, and no natural cycles are found in the observational record that can explain the observed changes in climate,” the report said, citing thousands of studies. “Evidence for a changing climate abounds, from the top of the atmosphere to the depths of the oceans.”

Scientists from all over the world have documented warming in the air and water, melting glaciers, disappearing snow, shrinking sea ice and rising sea level. The report said the United States will see temperature increases of at least 2.5 degrees over the next few decades, even with significant cuts to carbon pollution.

Even if humans stop spewing heat-trapping gases today, the world will warm another half a degree over today’s temperatures, the report said, citing high confidence in those calculations. Scientists, such as Stanford University’s Chris Field, say that even a few tenths of a degree of warming can have dramatic impacts on human civilization and the natural environment.

“Every increment in warming is an increment in risk,” said Field, who wasn’t part of the report but reviewed it for The National Academy of Sciences.

Trump, who has called climate change a “total con job” and “hoax” perpetrated to harm U.S. economic competitiveness, has spearheaded a wholesale scrapping of Obama-era initiatives that sought to reduce carbon emissions from coal-fired power plants and other sources. Last week, Trump’s administration formally told the United Nations the U.S. intends to pull out of the 2015 Paris climate accord, in which nearly 200 nations pledged to reduce carbon emissions.

Four co-authors of the federal climate assessment, who spoke to AP on the condition of anonymity, said they have not heard of or witnessed any attempt by the White House to suppress or censor the scientific document.


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