Climate change is already hurting the global economy and will cost the US hundreds of billions of dollars annually by 2050 unless drastic action is taken to cut carbon emissions, a major US government report has warned.

"By the middle of this century, annual losses in the United States due to climate change could reach hundreds of billions of dollars," said the latest edition of the National Climate Assessment.

"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," it said.

"The impacts of climate change beyond our borders are expected to increasingly affect our trade and economy, including import and export prices and US businesses with overseas operations and supply chains."

Compiled by more than 300 scientists, the Fourth National Climate Assessment Volume II is a congressionally mandated report that spans over 1,000 pages.

US President Donald Trump dismissed last year's report, and just this week appeared to confuse weather with climate change when he tweeted: "Brutal and Extended Cold Blast could shatter ALL RECORDS - Whatever happened to Global Warming?"