But the report said that if greenhouse gas emissions are sharply curbed, projections of further damage could change, even though many of the impacts of climate change - including more frequent and more powerful storms, droughts and flooding - are already under way. "Future risks from climate change depend primarily on decisions made today," it said.
The report supplements a study issued last year that concluded humans are the main driver of global warming and warned of potentially catastrophic effects to the planet.
The studies clash with policy under President Donald Trump, who has been rolling back Obama-era environmental and climate protections to maximize production of domestic fossil fuels, including crude oil, already the highest in the world, above Saudi Arabia and Russia.
White House spokeswoman Lindsay Walters said the new report was "largely based on the most extreme scenario, which contradicts long-established trends by assuming that...there would be limited technology and innovation, and a rapidly expanding population."
The government's next update of the National Climate Assessment, she said, "gives us the opportunity to provide for a more transparent and data-driven process that includes fuller information on the range of potential scenarios and outcomes."
Trump last year announced his intention to withdraw the United States from the 2015 Paris Deal agreed by nearly 200 nations to combat climate change, arguing the accord would hurt the U.S. economy and provide little tangible environmental benefit. Trump and several members of his cabinet have also repeatedly cast doubt on the science of climate change, arguing that the causes and impacts are not yet settled.
Environmental groups said the report reinforced their calls for the United States to take action on climate change.
"While President Trump continues to ignore the threat of climate change, his own administration is sounding the alarm," said Abigail Dillen, president of environmental group Earthjustice. "This report underscores what we are already seeing firsthand: climate change is real, it's happening here, and it's happening now."
Previous research, including from U.S. government scientists, has also concluded that climate change could have severe economic consequences, including damage to infrastructure, water supplies and agriculture.
Severe weather and other impacts also increase the risk of disease transmission, decrease air quality, and can increase mental health problems, among other effects.
Thirteen government departments and agencies, from the Agriculture Department to NASA, were part of the committee that compiled the new report.