WASHINGTON – A massive U.S. report concludes that the evidence of global warming is stronger than ever — contradicting top Trump administration officials who downplay humans’ role in climate change.
The report, released Friday, is one of two scientific assessments required every four years. A draft showing how warming affects the U.S. was also published.
David Fahey of the National Oceanic and Atmospheric Administration and several authors said there was no political interference or censoring of the 477-page report.
“A lot of what we’ve been learning over the last four years suggests the possibility that things may have been more serious than we think,” said Robert Kopp of Rutgers University, one of dozens of scientists inside and outside the government who wrote the reports.
Since 1900, Earth has warmed by 1 degree Celsius (1.8 degrees Fahrenheit) and seas have risen by 20 cm (8 inches). Heat waves, downpours and wildfires have become frequent.
Energy Secretary Rick Perry and Environmental Protection Agency chief Scott Pruitt have repeatedly said carbon dioxide isn’t the primary contributor to global warming.
But the scientists concluded that it is “extremely likely” — meaning with 95 to 100 percent certainty — that global warming is man-made, mostly from the spewing of carbon dioxide into the atmosphere from the burning of coal, oil and natural gas.
“Over the last century, there are no convincing alternative explanations,” the report said.
The scientists calculated that the human contribution to warming since 1950 is between 92 percent and 123 percent. The figure can top 100 percent because natural forces that cool the Earth, such as volcanoes and the orbital cycle, are overwhelmed by the effects of greenhouse gases, said study co-author Katharine Hayhoe of Texas Tech.
“This period is now the warmest in the history of modern civilization,” she said.
For the first time, scientists highlighted a dozen “tipping points” of potential dangers that could happen from warming.
They include the slowing down of the Atlantic Ocean circulation system, dramatically warping weather worldwide; much stronger El Ninos; major melting of ice sheets in Greenland and Antarctica, raising sea levels; and massive releases of methane and carbon dioxide from thawing permafrost, turbocharging warming.
Researchers did not provide an estimate of how likely tipping points would occur.
The report also documented how events caused by climate change can interact in complex ways to make life worse, such as the California wildfires and Superstorm Sandy five years ago.
The world’s oceans are under a “triple threat” — the water is getting warmer, more acidic and seeing a drop in oxygen levels, Hayhoe said.
In a 1,504-page draft report on the impacts of climate change, scientists detailed dozens of ways global warming is already affecting parts of the U.S.
Scientists said global warming is already sickening, injuring and killing Americans with changes to weather, food, air, water and diseases. And it’s expected to get worse, hurting the economy, wildlife and energy supply.
“Risks range from the inconvenient, such as increasing high tide flooding along the East Coast related to sea level rise, to …the forced relocation of coastal communities in Alaska and along the Gulf Coast,” the draft report said.
Outside experts said the reports are the most up-to-date summary of climate science.
“It shows that if anything the findings of scientists have become more dire” since 2013, said University of California, Berkeley climate scientist Zeke Hausfather, who wasn’t part of the work.
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