The National Climate Assessment, quietly unveiled on Friday, warned that natural disasters are worsening in the US because of global warming.
It said warming-charged extremes “have already become more frequent, intense, widespread or of long duration”.
The report noted the last few years have smashed US records for damaging weather, costing nearly 400 billion dollars (£312 billion) since 2015.
“I’ve seen it, I’ve read some of it, and it’s fine,” the Republican president told reporters at the White House. Asked about severe economic impacts, he said, “I don’t believe it.”
The president, administration officials and elected Republicans frequently say they cannot tell how much of climate change is caused by humans and how much is natural.
The report was issued on Black Friday, the day after Thanksgiving, when many Americans traditionally go shopping, a timing that Trump’s critics said was chosen to bury the report.
Last year, Trump announced his intent to withdraw the United States from the 2015 Paris deal to combat climate change, becoming the first country of 200 to do so. Due to UN rules, he cannot quit the deal until after the 2020 presidential election.
“Right now, we’re at the cleanest we’ve ever been and it’s very important to me,” Trump said. “But if we’re clean but every other place on Earth is dirty, that’s not so good.”
US carbon emissions from industry slipped 2.7 percent last year as coal plants shut and use of natural gas and renewable energy rose. But Trump’s critics said leaving the Paris agreement means the United States is allowing others to lead the global fight to curb climate change.
Trump has also rolled back Obama-era environmental and climate rules such as the Clean Power Plan, while seeking to boost output of oil, gas and coal for domestic use and for shipping to allies and partners. U.S. output of crude oil is already the highest in the world, above Saudi Arabia and Russia.
The report, written with the help of more than a dozen US government agencies and departments, said the effects of climate change would harm human health, damage infrastructure, limit water availability, and alter coastlines. Agriculture, tourism and fishing, industries that depend on natural resources and favourable climate conditions, would all be hit, it said.
The report also said projections of damage could change if greenhouse gas emissions were curbed, although many of the impacts of climate change, like powerful storms, droughts and flooding, have already begun.
The report supplements a study issued last year that concluded humans are the main driver of global warming and warned of catastrophic effects to the planet.