WASHINGTON — Directly contradicting much of the Trump administration's position on climate change, 13 federal agencies unveiled an exhaustive scientific report Friday that says humans are the dominant cause of the global temperature rise that has occurred since the start of the 20th century, creating the warmest period in the history of civilization.
Over the past 115 years, global average temperatures have increased 1.8 degrees Fahrenheit, leading to record-breaking weather events and temperature extremes, the report says. The global, long-term warming trend is "unambiguous," it says, and there is "no convincing alternative explanation" that anything other than humans — the cars we drive, the power plants we operate, the forests we destroy — are to blame.
The report was approved for release by the White House, but the findings come as the Trump administration is defending its climate change policies on several fronts. The United Nations convenes its annual climate change conference next week in Bonn, Germany, and the U.S. delegation is expected to face harsh criticism over President Donald Trump's decision to walk away from the 195-nation Paris climate accord and top administration officials' stated doubts about the causes and impacts of a warming planet.
"This report has some very powerful, hard-hitting statements that are totally at odds with senior administration folks and at odds with their policies," said Philip B. Duffy, president of the Woods Hole Research Center. "It begs the question, where are members of the administration getting their information from? They're obviously not getting it from their own scientists."
While there were pockets of resistance to the report in the Trump administration, there was little appetite for a knockdown fight over climate change among Trump's top advisers, who are intensely focused on passing a tax reform bill — an effort they think could determine the fate of his presidency.
The climate science report is part of a congressionally mandated review conducted every four years known as the National Climate Assessment. The product of hundreds of experts within the government and academia and peer-reviewed by the National Academy of Sciences, it is considered the United States' most definitive statement on climate change science.
That has not stopped the Environmental Protection Agency from wiping references to climate change from its website and barring its scientists from presenting scientific reports on the subject.
EPA administrator Scott Pruitt has said carbon dioxide is not a primary contributor to warming. Rick Perry, the energy secretary, asserted Wednesday that "the science is out" on whether humans cause climate change.
Their agencies referred questions to the National Oceanic and Atmospheric Administration, which oversaw the research.
The White House put out a statement Friday that seemed to undercut the high level of confidence of the report's findings.
"The climate has changed and is always changing," Raj Shah, a White House spokesman, said in the statement. "As the Climate Science Special Report states, the magnitude of future climate change depends significantly on 'remaining uncertainty in the sensitivity of Earth's climate'?" to greenhouse gas emissions, he added.
But scientists said the report's findings were clear.
"This new report simply confirms what we already knew. Human-caused climate change isn't just a theory, it's reality," said Michael E. Mann, a professor of atmospheric science at Pennsylvania State University. "Whether we're talking about unprecedented heat waves, increasingly destructive hurricanes, epic drought and inundation of our coastal cities, the impacts of climate change are no longer subtle. They are upon us. That's the consensus of our best scientists, as laid bare by this latest report."