At Jim Benham's soybean farm in Versailles, Indiana, he says 20 acres of crops have been ruined this year by excessive rain – a casualty of climate change.

"It's like chewing gum; they're just too wet," he said of the soybeans too soggy to harvest — they'd turn to paste if he tried.

And what's worse, the 67-year-old farmer says he doesn't need a Ph.D. to know that things have changed. "When we have a rain event, we're not getting an inch; we're getting two and three and four inches," Benham said. "It doesn't take a scientist to know you have a problem. It's what I'm experiencing."

Indiana soybean farmer Jim Benham says 20 acres of crops have been ruined this year by excessive rain. CBS News

Scientists agree. A new government report says man-made climate change is already wreaking havoc on the U.S., and it will only get worse in the coming decades. In the Fourth National Climate Assessment, issued Friday, 13 federal agencies warn that climate change "will reduce Midwest agricultural productivity to levels of the 1980s."

The report also warns of more destructive Western wildfires, longer heat waves in the Southeast, and more powerful Atlantic hurricanes. It says climate change could shrink the U.S. economy by hundreds of billions of dollars by the end of the century.

Andrew Light, one of the report's editors, says the evidence humans are causing climate change is undeniable.

"The part of the country that's going to get worse fastest is actually the Midwest, which is the breadbasket of America," he said.

The rest of the country doesn't fare much better. The report says sea levels around the U.S. have risen about nine inches. By 2090, rising seas would cause $118 billion in property damage each year.

Heat waves now last more than 40 days longer than they did in the 1960s.

By 2090, outdoor workers could lose $160 billion in wages from extreme heat.

In 2015, wildfires burned more than 10.1 million acres – that's larger than the state of Maryland. This year, massive, deadly wildfires, like the Camp Fire, left California devastated, and the report warns of hotter, drier conditions to come in the West.

"Towards the end of the century, you could see the United States economy losing hundreds of billions of dollars every single year, and tens of thousands of Americans dying every single year because of climate change," said Light.

"This is all avoidable at this point."

Yet last year, President Trump, who has called man-made climate change a "hoax," announced he was pulling the U.S. out of the Paris climate accord, saying it would be unfair to American businesses.

Editor's Note: An earlier version of the story text stated the farm was in Illinois, but it has been corrected to Indiana.

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