The harmful effects of global warming are being felt "here and now and in your backyard," a groundbreaking US government report on climate change warned Tuesday.

"Climate change is happening now, it is not something that will happen decades or centuries in the future," Jerry Melillo of the Marine Biological Laboratory in Massachusetts, one of the lead authors of the report, told AFP.

Climate change, which the report blames largely on human-induced emissions of heat-trapping gases, "is under way in the United States and projected to grow," said the report by the US Global Change Research Program, a grouping of a dozen government agencies and the White House.

The report is the first on climate change since President Barack Obama took office and outlines in plain, non-scientific terms how global warming has resulted in an increase of extreme weather such as the powerful heatwave that swept Europe in 2003, claiming tens of thousands of lives.

Hurricanes have become fiercer as they gather greater strength over oceans warmed by climate change.

Global warming impacts everything from water supplies to energy, farming to health. And those impacts are expected to increase, according to the report titled "Global Change Impacts in the United States."

Areas of the country that already had high levels of rain or snowfall have seen increases in precipitation because of climate change, says the report, which focuses on the United States but also tackles global climate change issues.

"We focused on regions of the US because another big message we wanted to get across is that not only is climate change happening now, but it's happening in your backyard," said Melillo.

"You care a great deal more about a tornado in your own backyard than one half a world away," said David Doniger, senior policy director at the National Resources Defense Council (NRDC).

Arid areas, such as the largely desert US Southwest, are experiencing more droughts.

On the US Gulf Coast, sea level rise is particularly pressing; in the Northwest, how long snowpack sits on the mountains might be an issue, and farmers in the Midwest are concerned because winters have become milder, allowing more pests to survive the season.

But climate change also operates in a global nexus and the United States cannot be viewed in isolation, the 196-page report says.

Climate change-related food production problems in one part of the world can affect food prices and production decisions in the United States, he added.

"There is a whole host of connections when you discuss climate change; the US cannot be viewed as an island," Melillo said.

The chief aim of the report is to help US policymakers and the general public make decisions on how to act to halt climate change, Melillo said.

The report's release comes just six months before countries from around the world meet in the Danish capital Copenhagen for a UN conference that aims to produce an ambitious, new climate pact aimed at rolling back global warming.

Experts have been thrashing out a draft of a negotiating text for the new pact meant to take effect from the end of 2012, spelling out curbs on emissions by 2020 that will be deepened by 2050.

Reports issued by the previous administration of president George W. Bush -- who famously rejected the Kyoto Protocol, the previous UN framework on climate change -- were highly technical and did not cover as many issues as the sweeping first report issued by the Obama White House, said Melillo.

The report stresses the need for immediate action against global warming, saying: "Future climate change and its impacts depend on choices made today."

"We have the power to determine how bad this could be and to avoid the worst impacts of global warming," said Doniger.

"It's like Charles Dickens' 'A Christmas Carol,' where the ghosts come and show Scrooge the way the future could unfold into either a happy future or a disastrous future.

"This shows us that the future is in our hands, just as it was in Scrooge's hands," said Doniger.