The U.S. government's climate scientists issued a blunt warning on Friday, writing that global warming is a growing threat to human life, property and ecosystems across the country, and that the economic damage—from worsening heat waves, extreme weather, sea level rise, droughts and wildfires—will spiral in the coming decades.

The country can reduce those costs if the U.S. and the rest of the world cut their greenhouse gas emissions, particularly the burning of fossil fuels. Capping global greenhouse gas emissions to limit warming to 2 degrees Celsius (3.6°F) or less would avoid hundreds of billions of dollars of future damages, according to the Fourth National Climate Assessment, written by a science panel representing 13 federal agencies.

The report, like a recent comprehensive assessment issued by the United Nations, signaled the mounting urgency for governments to act quickly to reduce greenhouse gas emissions before locking in high risks. And it underscored, without saying so directly, how the Trump administration is moving in the opposite direction.

The agencies write that global warming is:

Intensifying and increasing the frequency of extreme rainstorms that cause devastating flooding and crop losses.

Putting people and economies at risk as temperatures rise : Increases in extreme heat waves could kill up to 2,000 more people per year in the Midwest alone by 2090, and Chicago's climate could be more like Phoenix, with temperatures reaching 100°F on 50 to 60 days in summer.

Increasing the drying of land and vegetation, which puts crops at risk and contributes to deadly wildfires.

Harming U.S. forests , making them more vulnerable to fire and insects, disrupting their watersheds and wildlife habitat, and also reducing their ability to store carbon.

Putting water supplies and water quality at risk, with "significant changes already evident across the country," including more pollution runoff from extreme rainfall that, along with warmer water, fuels and toxic algae blooms.

Creating multiple threats for coastal communities , including significant shifts in fish populations, ocean acidification, direct flooding damage from rising sea level and tropical storms. Along the coasts, $1 trillion in public infrastructure and private property are threatened by flooding, rising sea level and storm surges.

Threatening indigenous peoples' livelihoods and economies by affecting fishing, agriculture and forestry.

The report looks at the damage already happening and what's ahead in each region, describing damage from wildfires and the impact of ocean acidification on shellfish in the Northwest; rising temperatures thawing permafrost in Alaska; coral reef damage in Hawaii; hurricanes, coastal flooding and mosquito-borne diseases in the Southeast; extreme rainfall destroying crops and eroding farm soil in the Midwest; flash droughts in the Northern Plains; and the dwindling of the snowpack and the Colorado River that the Southwest relies on.

U.S. temperatures have already risen about 1.8°F (1°C) since the start of the Industrial era, and that warming has been accelerating in recent decades. "Recent record-setting hot years are projected to become common in the near future for the United States," the report says.

"It drives home the fact that climate change isn't a far off threat," said Pennsylvania State University Climate researcher Michael Mann.

The report also shows how global warming impacts will be multiplied by disruptions to energy, transportation and other infrastructure that cascade across economic sectors, said National Oceanic and Atmospheric Administration scientist David Easterling, a lead author for the climate science section.

For example, heat waves and droughts can cut energy production if there is not enough water to cool power plants, which can limit manufacturing and even affect health care in hospitals. Hurricane Harvey's damage to power infrastructure affected water treatment plants and refineries, shutting down 11 percent of U.S. oil refining capacities and causing a temporary spike in gas prices.

Industries that rely on natural resources are especially vulnerable.

"Without significant reductions in greenhouse gas emissions, extinctions and transformative impacts on some ecosystems cannot be avoided, with varying impacts on the economic, recreational, and subsistence activities they support," Easterling said.

Huge Economic Costs, and They're Rising

With detailed projections for geographic regions, scientists can now also project the multibillion-dollar costs of global warming impacts based on robust data, said Philip Mote, a climate researcher at Oregon State University who worked on the report.

"We're finally seeing a lot more economic data. In the past, we could talk about, well this is going to happen, there will be lower streamflow(s), there will be more invasive species, this might happen, that might happen," he said. Now, more economic studies show the rising costs. In the worst-case scenario, global warming costs could total 10 percent of U.S. GDP by the end of the century, according to research cited in the report.



How much those costs can be reduced will depend on how fast emissions of both carbon dioxide and short-lived climate pollutants like methane and HFCs are reduced and land-based carbon storage is ramped up.

"Decisions that decrease or increase emissions over the next few decades will set into motion the degree of impacts that will likely last throughout the rest of this century, with some impacts (such as sea level rise) lasting for thousands of years or even longer," the report says. "Early mitigation can reduce climate impacts in the nearer term (such as reducing the loss of perennial sea ice and effects on ice-dwelling species) and, in the longer term, prevent critical thresholds from being crossed (such as marine ice sheet instability and the resulting consequences for global sea level change)."

The release of the report suggests federal science has fared better then expected in the past two years, "due in part to some degree of bipartisan resolve that still remains when it comes to governmental support for science," Mann said.

But that doesn't offset the harm caused by the dismantling of environmental protections and green-lighting of climate-unfriendly energy policies at the Departments of Energy and Interior and elsewhere, he said.

The severe damage caused by recent record floods from Hurricanes Harvey and Florence, as well as the catastrophic California wildfires, also suggest that "models aren't completely capturing the physics relevant to understanding and projecting these unprecedented weather extremes," Mann said.

Atmospheric scientist Kevin Trenberth, with the National Center for Atmospheric Research, also said that climate impact assessments in general tend to under-emphasize the effect of global warming on climate extremes.

"A lot more is attributable than is generally accepted," Trenberth said, citing recent research he worked on showing links between deep ocean heat content and the damaging floods from Hurricane Harvey. In the Pacific, global warming is likely to intensify El Niños, with "bigger and with stronger droughts and floods around the world."

And the U.S. is still behind the curve when it comes to responding to the growing threat.

Up to now, "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 over the coming decades," the report concludes.

Farms and Food System at Higher Risk

The report stressed that American farmers and ranchers are already feeling the effects of climate change, and that those effects will worsen dramatically, with more extreme rainfall, flooding and drought.

"The farm and food system as we know it is transforming before our eyes, and the productivity we've benefited from is in jeopardy," explained Marcia DeLonge, a senior scientist with the Union of Concerned Scientists. "We're going to lose commodity crops—due to different growing seasons, droughts, floods, and the costs to farmers and ranchers—and taxpayers—will be huge. And we're likely underestimating them."

Climate change will hit the Corn Belt particularly hard. Under a high-emissions scenario, the Midwest will see greater increases in warm-season temperatures than anywhere else in the country, with the frost-free season projected to increase by an average of 10 days from 2016 to 2045.

A rise in temperatures in the Midwest is "projected to be the largest contributing factor to declines in the productivity of U.S. agriculture," the report says. Agricultural productivity could drop to 1980s levels by 2050, the report said, essentially wiping out gains made in recent decades from improved technologies.

Millions of People Become More Vulnerable

World Resources Institute scientist Andrew Light, an author of the mitigation chapter, said it's clear the report is at odds with the administration's policy and with what President Trump says about climate change.

But that doesn't change the fact that millions of people are becoming more vulnerable to global warming impacts.

"We need to be reaching a point in this country where we are arguing about the best solutions, not over whether a problem exists. This report creates very clear terrain around which one could have this discussion," Light said.

He said some of the regional findings make it clear what's at stake for people. In New England, under a high emissions scenario, the distinctive seasons of New England could disappear, altering the region's fundamental character.

"It's hard to imagine there won't be distinct seasons. That indelibly changes the place," he said.

And in his native state of Georgia, the report identifies a growing risk of wildfires.

"That's incredibly distressing. It's not part of our annual cycle, we don't have a forest fire season in the Southeast, so it's horrible to imagine those kinds of impacts if you think about what we're seeing in California right now."

The 2016 wildfire that burned through Gatlinburg, Tennessee, is a prime example of how communities can be caught unaware of the risks.

"The people were not ready at all, and the changes that create this type of risk could happen quickly," Light said.

Was Trump Trying to Bury the Warnings?

The report is based on thousands of climate studies and is written by the U.S. Global Climate Change Research Program, which includes scientists and policy experts from 13 federal agencies. A 1990 law created the program and mandates regular climate assessments.

The release of the report was originally scheduled for early December, but the date was moved up to the day after Thanksgiving, Black Friday, sometime during the past week, leading to concerns that the Trump administration meant to bury the report by publishing it during a holiday weekend. That drew scorn from some politicians.

"No matter how hard they try, the Trump administration can't bury the effects of climate change in a Black Friday news dump – effects their own federal government scientists have uncovered," said Sen. Sheldon Whitehouse, a Democrat from Rhode Island.

"This report shows how climate change will affect every single one of our communities," he said. "The president says outrageous things like climate change is a hoax engineered by the Chinese and raking forests will prevent catastrophic wildfires, but serious consequences like collapsing coastal housing prices and trillions of dollars in stranded fossil fuel assets await us if we don't act."

InsideClimate News reporter Georgina Gustin contributed to this report.