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.
“Evidence for a changing climate abounds, from the top of the atmosphere to the depths of the oceans,” 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 a special science section of the National Climate Assessment, which is congressionally mandated every four years. The National Academy of Sciences has signed off on the draft report, and the authors are awaiting permission from the Trump administration to release it.
The White House and the Environmental Protection Agency did not immediately return calls or respond to emails requesting comment on Monday night.
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. The projected actual rise, scientists say, will be as much as 2 degrees Celsius.
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.
In the United States, the authors write, the heat wave that broiled Texas in 2011 was more complicated. That year was Texas’ driest on record, and one study cited in the report said local weather variability and La Niña were the primary causes, with a “relatively small” warming contribution. Another study had concluded that climate change made extreme events 20 times more likely in Texas.
Based on those and other conflicting studies, the federal draft concludes that there was a medium likelihood that climate change played a role in the Texas heat wave. But it avoids assessing other individual weather events for their link to climate change. Generally, the report described linking recent major droughts in the United States to human activity as “complicated,” saying that while many droughts have been long and severe, they have not been unprecedented in the earth’s hydrologic natural variation.
Worldwide, the draft report finds it “extremely likely” that more than half of the global mean temperature increase since 1951 can be linked to human influence.