A major climate change report released Friday afternoon by the Trump administration says that it is “extremely likely” that human activities are the “dominant cause” of global warming.
“For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence,” the report says.
In addition, the report says that the past 115 years are “the warmest in the history of modern civilization."
The comprehensive study of climate science by U.S. government researchers across 13 federal agencies, known as the Climate Science Special Report, is part of a larger scientific review called the fourth National Climate Assessment. It is mandated by Congress to be released every four years.
The findings contradict the Trump administration’s doubts about climate science and most scientists' belief that humans are the largest contributor of greenhouse gases that cause global warming.
"This new report reaffirms the overwhelming consensus of the world’s scientists, namely that climate change is real, human-caused, and already having dramatic impacts on us and our planet," said Michael Mann, a professor of atmospheric science at Penn State University, in an email to the Washington Examiner. "Whether it's unprecedented superstorms, more intense heat waves, epic drought or the inundation of our coastlines from the sea level rise, the impacts of climate change are no longer subtle. We are seeing them play out in real time, as this report makes clear."
The scale of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases emitted globally, the report said.
Without major reductions in emissions, the increase in annual average global temperature relative to pre-industrial levels could reach 9° Fahrenheit, or 5° Celsius, or more by the end of the century.
But with significant reductions in emissions, the increase in annual average global temperature could be limited to 3.6°F, or 2°C, or less, the report said.
The Trump administration has repealed or moved to review a number of Obama-era regulations intended to reduce emissions, including the Clean Power Plan restrictions on power plants.
EPA Administrator Scott Pruitt last month announced his intent to repeal the Clean Power Plan and said the Obama administration had exceeded its legal authority in creating it. The plan, which was stayed by the Supreme Court in February 2016 and never implemented, required states to reduce carbon emissions by 32 percent below 2005 levels by 2030, with a focus on preventing pollution from coal-fired power plants.
Pruitt also has removed an EPA web page focused on climate change and is encouraging the concept of a "Red Team/Blue Team" exercise, in which two groups of experts debate the science behind climate change.
The White House on Friday downplayed the report's findings.
In a statement, White House Principal Deputy Press Secretary Raj Shah said that “the climate has changed and is always changing.”
“The administration supports rigorous scientific analysis and debate and encourages public comment on the draft documents being released today,” Shah said. “To address climate change as well as other risks, the U.S. will continue to promote access to the affordable and reliable energy needed to grow economically, and to support technology, innovation and the development of modern and efficient infrastructure that will reduce emissions and enable us to address future risks, including climate related risks."
The new government report says the effects of a warming climate are already clear.
It says thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric and oceanic temperatures, melting glaciers, diminishing snow cover, shrinking sea ice; rising sea levels, ocean acidification, and increasing atmospheric water vapor.
For example, global average sea level has risen by about seven to eight inches since 1900, with almost half of that rise occurring since 1993.
Global average sea levels are expected to continue to rise, by at least several inches in the next 15 years and by one to four feet by 2100.
Heatwaves have also become more frequent in the United States since the 1960s, while extreme cold temperatures are less common.
In addition, wildfires have occurred more often in the western United States and Alaska since the early 1980s and are projected to further increase in those regions as the climate changes, the report says.
This year has been the most expensive firefighting season ever recorded for the federal government.
Joseph Majkut, director of climate policy at the Niskanen Center, a free market think tank, said he doesn't expect the Trump administration to change its approach despite the report's conclusions.
“I don't sense the release of this report is a big watershed moment, and I and don't think it will put anyone in a political jam," Majkut told the Washington Examiner in an interview. “This is stuff we know already. I would like to see it inspire some more consideration of climate risk. But I am not holding my breath. My guess is it's a relative non-event."
The report has been submitted to the Office of Science and Technology Policy at the White House. Trump has yet to nominate anyone to run that office.
A group of Democratic senators this week called on the Trump administration to refrain from "political interference" and not suppress the report. The New York Times had previously reported that many scientists who worked on the climate report feared that the Trump administration would try to suppress it.