Asked outside the White House about the findings that unchecked global warming would wreak havoc on the US economy, he said: “I don’t believe it.”
The report found that climate change will cost the US hundreds of billions of dollars annually and damage health.
The Trump administration has pursued a pro-fossil fuels agenda.
The world’s leading scientists agree that climate change is human-induced and warn that natural fluctuations in temperature are being exacerbated by human activity.
What did President Trump say?
He told reporters on Monday that he had “read some of” Friday’s report, which was compiled with help from US government agencies and departments.
Mr Trump said other countries must take measures to cut their emissions.
“You’re going to have to have China and Japan and all of Asia and all these other countries, you know, it [the report] addresses our country,” he said.
“Right now we’re at the cleanest we’ve ever been and that’s very important to me.
“But if we’re clean, but every other place on Earth is dirty, that’s not so good.
“So I want clean air, I want clean water, very important.”
Former Democratic presidential candidate Hillary Clinton accused the Trump administration of trying to hide the report.
What did the reportsay?
The Fourth National Climate Assessment outlines the potential impacts of climate change across every sector of American society.
“With continued growth in emissions at historic rates, annual losses in some economic sectors are projected to reach hundreds of billions of dollars by the end of the century – more than the current gross domestic product (GDP) of many US states,” the report says.
“Without substantial and sustained global mitigation and regional adaptation efforts, climate change is expected to cause growing losses to American infrastructure and property and impede the rate of economic growth over this century.”
The report notes that the effects of climate change are already being felt in communities across the country, including more frequent and intense extreme weather and climate-related events.
But it says that projections of future catastrophe could change if society works to reduce greenhouse gas emissions and “to adapt to the changes that will occur”.
What has President Trump previously said on climate change?
In October, President Trump accused climate change scientists of having a “political agenda”, telling Fox News he was unconvinced that humans were responsible for the earth’s rising temperatures.
After taking office he announced the US would withdraw from the Paris climate change agreement, which commits another 187 other countries to keeping rising global temperatures “well below” 2C above pre-industrial levels.
At the time, Mr Trump said he wanted to negotiate a new “fair” deal that would not disadvantage US businesses and workers.
During his election campaign in 2016 Mr Trump said climate change was “a hoax”. However he has since rowed back on that statement saying in a recent interview: “I don’t think it’s a hoax, I think there’s probably a difference.”
How great is the climate threat?
A report released in October by the Intergovernmental Panel on Climate Change (IPCC) – the leading international body evaluating climate change – said it could be stopped only if the world made major, and costly, changes.
That means reducing global emissions of CO2 by 45% from 2010 levels by 2030, and reducing coal use to almost zero and using up to seven million sq km (2.7 million square miles) for land energy crops.
If the world fails to act, the researchers warned, there would be some significant and dangerous changes to our world, including rising sea levels, significant impacts on ocean temperatures and acidity, and the ability to grow crops such as rice, maize and wheat.