The White House has sought to downplay a major climate change report, which was compiled by 13 US federal agencies.
The study is at odds with assertions from President Donald Trump and several members of his administration.
It says it is "extremely likely" human activity is the "dominant cause" of global warming.
A spokesman for the White House said it supported "rigorous scientific analysis and debate" but added that the climate was "always changing".
White House principal deputy press secretary Raj Shah said it was not certain how sensitive the Earth's climate was to greenhouse gas emissions.
Mr Trump, who has embarked on a tour of Asia, once said the concept of global warming was created by the Chinese in order to make American manufacturing less competitive.
Earlier this year, he announced he was pulling the US out of the Paris Agreement to cut global emissions.
The Climate Science Special Report, which was approved by the White House, was compiled by US government scientists.
It argues that it is "extremely likely" that human activity is causing rapid global warming with dire consequences for the US and the world.
The scientists' predictions include:
- A global sea level rise of up to 8ft (2.4 metres) cannot be ruled out by the end of the century
- Risks of drought and flooding will increase
- There will be more frequent wildfires and devastating storms
Running to nearly 500 pages, the report concludes that the current period is "now the warmest in the history of modern civilisation".
It is "extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause", it finds, adding that "there is no convincing alternative explanation".
President Trump has made it easier for industry to pollute and he has appointed to key government positions men who are sceptical of their own scientists, the BBC's James Cook, in Los Angeles, says.
Only on Thursday, Mr Trump's Energy Secretary, Rick Perry, told US media that while he thought climate change was real and humans had an "impact on it", he still thought "the science [was] out on" whether humans cause 100% of it.
The researchers say there was no political interference in, or censorship of, their report.
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