The impact of global climate change is being felt across the country and, unchecked, could cause U.S. economic losses totaling hundreds of billions of dollars a year by the end of the century, says a new U.S. government report released Friday.

Many U.S. communities and companies are trying to counteract the effects of rising temperatures ranging from water shortages or flooding to worsening wildfires and air pollution. But those measures so far fall short, according to the latest installment of the U.S. National Climate Assessment.

“Neither global efforts to mitigate the causes of climate change nor regional efforts to adapt to the impacts currently approach the scales needed to avoid substantial damages to the U.S. economy, environment, and human health and well-being,” the report said.

The federal report concludes “that the evidence of human-caused climate change is overwhelming and continues to strengthen, that the impacts of climate change are intensifying across the country, and that climate-related threats to Americans’ physical, social, and economic well-being are rising.”

Mandated by law since 1990, the official climate assessment is produced every four years by the U.S. Global Change Research Program to guide federal policy makers. The new edition, released in English and Spanish, highlights the local impact of rising temperatures across the U.S.

“This report makes it clear that climate change is not some problem in the distant future. It’s happening right now in every part of the country. When people say the wildfires, hurricanes and heat waves they’re experiencing are unlike anything they’ve seen before, there’s a reason for that, and it’s called climate change,” said Brenda Ekwurzel, climate science director at the Union of Concerned Scientists and a report author.

Its conclusions are at odds with statements by President Trump, who has been skeptical of global-warming trends, questioned the validity of climate science, and challenged federal regulations designed to control greenhouse-gas emissions.

“There has been no external interference in the development of this report,” said David Easterling, director of the technical support unit at the National Centers for Environmental Information, who helped prepare the 1,500-page assessment.

In all, more than 300 experts guided by a 60-member Federal Advisory Committee produced the report. It was then reviewed by most federal agencies, including the National Oceanic and Atmospheric Administration, the National Aeronautics and Space Administration, the Energy Department and the Environmental Protection Agency. The report’s authors also conducted regional workshops in over 40 cities.

The resulting formal federal climate assessment builds on a previous installment released last year that evaluated the underlying science on which climate change predictions are based.

All told, 17 of the 18 warmest years on record have occurred since 2000. NASA researchers ranked 2017 as the second-warmest year since 1880, while NOAA scientists ranked it as the third-warmest. So far in 2018, U.S. temperatures for the year-to-date are the 10th-warmest on record, according to the National Centers for Environmental Information.

Broadly, the warming trend has been driven in large part by land-use changes, including cutting down forests and paving over natural surfaces, and rising emissions of greenhouse gases, including carbon dioxide from the burning of fossil fuels and methane from livestock production, scientists say.

In a separate federal report released Friday, researchers concluded that fossil-fuel emissions in North America have been declining steadily for the past decade, due to a reduced reliance on coal, greater use of natural gas, and increased vehicle fuel-efficiency standards.

As a result, North America’s share of global carbon emissions dropped from 24% in 2004 to about 17% in 2013, said William Hohenstein, director of the Office of Energy and Environmental Policy at the U.S. Department of Agriculture.

But global emissions overall continued to rise.

“Observations collected around the world provide significant, clear, and compelling evidence that global average temperature is much higher, and is rising more rapidly, than anything modern civilization has experienced, with widespread and growing impacts,” the climate assessment report said.

“The warming trend observed over the past century can only be explained by the effects that human activities, especially emissions of greenhouse gases, have had on the climate,” it said.

Write to Robert Lee Hotz at sciencejournal@wsj.com