The most dire government warning yet about climate change, released today, says that people are feeling the effects of warming here and now in the United States.

The National Climate Assessment, produced every four years by the U.S. Global Change Research Program, is the third report in the current series that outlines the present and ongoing effects of climate change on the country.

Citing record temperatures in the last decade, heavy rainfall and flooding in some places and drought in others, more frequent and stronger hurricanes, as well as winter storms, the report states: "Global climate is changing and this is apparent across the United States in a wide range of observations. The global warming of the past 50 years is primarily due to human activities, predominantly the burning of fossil fuels."

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"Climate change is not a distant threat; it's already affecting every region of the country and economy," said John Holdren, assistant to the president for science and technology and director of the Office of Science and Technology Policy, today at a White House press conference.

Looking to future climate, the report states that temperatures will continue to rise over the next several decades, given the climate-changing gases that are in Earth's atmosphere. How much they will rise after that depends on how much humans curtail the release of the gases that cause climate change.

If emissions can be kept in check, temperatures could rise as much as 6 degrees Fahrenheit in parts of the United States in the last few decades of the century. If emissions rise, the nation starts to look very hot, with much of the country -- especially the interior -- roasting under 8 to 9 degree rises in average heat levels.

And those higher temperatures have wideranging effects, the report warned. "The types and magnitudes of impacts vary across the nation and through time. Children, the elderly, the sick, and the poor are especially vulnerable. There is mounting evidence that harm to the nation will increase substantially in the future unless global emissions of heat-trapping gases are greatly reduced," the report said.

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Among specific predictions in the study for the last few decades of this century:

  • Wet regions will get wetter and drier regions drier:

  • Global sea levels will rise from 1 to 4 feet, swamping low-lying regions.

  • Strong storms will become more frequent, causing infrastructures and systems to collapse, similar to what happened in New Orleans during Hurricane Katrina.

  • Human health will be threatened by extreme weather, wildfires, decreased air quality, threats to mental health, and illnesses transmitted by food, water, and disease-carriers such as mosquitoes and ticks.

Kim Knowlton, co-deputy director of the Natural Resources Defense Council's Science Center and senior scientist in NRDC’s health and environment program, said in a press release: “This report shows how climate change’s effects are now firmly in the present, posing threats to our health -- and that of our children, and their children.

"Rising temperatures increase the frequency and intensity of dangerous heat waves, worsen illnesses like asthma, contribute to the spread of insects that carry infectious diseases, and fuel more dangerous storms and flooding.

"We have important opportunities now to limit climate change’s worst effects by cutting carbon emissions. At the same time, we can prepare to deal with what’s happening now, and for what’s coming, to protect communities and people. ”

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The report is robust: Over 300 experts produced it under the guidance of a 60-member Federal Advisory Committee. The report was extensively reviewed by other experts and included public comments. A panel of the National Academy of Sciences also reviewed the report.

To read it, you can go here. You might want to brace yourself.