“For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.”
Reports suggested there was concern among scientists that the report by the National Oceanic and Atmospheric Administration might suffer from political interference from the White House. Instead, the scientists said there was none.
The Associated Press said the 447-page report, one of two scientific assessments required every four years, is the most comprehensive summary of climate science since 2013.
During the election campaign and since assuming office, Mr Trump has rejected much climate change science as “a hoax”. Earlier this year, he withdrew the US from the Paris Accord, placing the country alone with Syria as the two nations that have refused to be part of it.
“A lot of what we've been learning over the last four year suggests the possibility that things may have been more serious than we think,” said Robert Kopp of Rutgers University, one of the dozens of scientists inside and outside the government who wrote the studies.
Since 1900, the earth has warmed by 1C degree and seas have risen by 8 inches. Heat waves, downpours and wildfires have become frequent, the report noted.
Energy Secretary Rick Perry and Environmental Protection Agency chief Scott Pruitt, have repeatedly said carbon dioxide is not the primary contributor to global warming.
Yet, the scientists who wrote the report said it was extremely likely - that is, to a level of certainty between 95 to 100 per cent - that global warming was man-made, mostly from the spewing of carbon dioxide into the atmosphere from the burning of coal, oil and natural gas.
For the first time, scientists highlighted a dozen “tipping points” of potential dangers that could happen from warming, things that co-author Katharine Hayhoe of Texas Tech University, said “keep me up at night”.
They include the slowing down of the giant Atlantic Ocean circulation system that could dramatically warp weather worldwide, much stronger El Ninos, major decreases in ice sheets in Greenland and Antarctica, which would spike sea level rise, and massive release of methane and carbon dioxide from thawing permafrost that could turbo-charge warming.
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