Climate change has moved from the corners of the earth into the American backyard, the country's leading scientists warned on Tuesday, releasing a landmark report they hoped would spur action on climate change.

The 840-page National Climate Assessment was seen as the definitive account of the effects of climate change on America, and of the country's efforts to deal with climate change.

The findings were immediately embraced by the White House as “actionable science” which would guide Barack Obama as he moves to cut carbon emissions from power plants next month and for the remaining two years of his presidency.

“I think this National Climate Assessment is the loudest and clearest alarm bell to date signalling the need to take urgent action to combat the threats to Americans from climate change,” John Holdren, the White House science advisor, told a conference call with reporters.

Scientists who worked on the report said its main messsage was that climate change was already disrupting the lives of Americans – now and in real-time – and was doing so much more strongly than scientists had expected.

Climate change was already registering in the form of extreme weather, sea-level rise, and the thawing of Arctic sea ice, a shift in growing seasons, and other indicators, the report said.

“What this report shows is that climate change is happening now in our own backyards,” Thomas Karl, the director of the climatic centre at the National Oceanic and Atmospheric Administration, told the Guardian. “There are a number of changes that have become faster and more apparent and stronger than we first anticipated.”

The report for the first time looks at what America is doing to cut the emissions that cause climate change, and to protect people from its consequences in the future. It said all Americans are experiencing and will continue to experience the effects of climate change.

"Climate change, once considered an issue for a distant future, has moved firmly into the present," the report said. "Corn producers in Iowa, oyster growers in Washington state and maple syrup producers in Vermont are all observing climate-related changes that are outside of recent experience."

The report is a compilation of published peer-reviewed science of the last several years, and details the effects of climate change on eight regions in the US. It notes that average temperature in the US has increased by about 1.5F (0.8C) since 1895, with more than 80% of that rise since 1980. The last decade was the hottest on record in the US.



Temperatures are projected to rise another 2F over the next few decades, the report says. In northern latitudes such as Alaska, temperatures are rising even faster. Some parts of the country will be harder hit than others.

Record-breaking heat – even at night – is expected to produce more drought and fuel larger and more frequent wildfires in the south-west, the report says. The north-east, midwest and Great Plains states will see an increase in heavy downpours and a greater risk of flooding. The north-east saw a 70% rise in heavy rainfall events in the last 60 years, the report said.

Sea-level rise, which could reach 4ft by the end of the century, was already causing dangerous flooding in low-lying areas like Miami, Norfolk, Virginia, and Portsmouth, New Hampshire, the report said. Florida alone could face a $130 billion bill for flooding damage by the year 2100.



Drought and high temperatures were already baking California and Arizona and prolonging the fire season in other parts of the south-west.

In California, warmer winters have made it difficult to grow cherries. In the midwest, wetter springs have delayed planting. Invasive vines such as kudzu have spread northward, from the south to the Canadian border.



Some of the effects on agriculture, such as a longer growing season, are positive. But "by mid-century and beyond the overall impacts will be increasingly negative on most crops and livestock."



The report also warned of a growing risk of contaminated water supply because of sea-level rise and flooding, and poor air quality as hotter temperatures cook the smog, and soot from wildfires drifts across the country. Those with allergies are facing longer pollen and ragweed seasons – by as much as 24 days in North Dakota and Minnesota, the report said.

“I think maybe this report will be the turning point when people finally realise that this is about them,” Susan Hassol, the chief science writer on the report, told the Guardian. “It's about them and their lives … Earlier, they had seen it as a distant threat – distant in time, distance in space, this is about poles, this is about island nations. They haven't seen it as a threat in their own backyard.”

The White House moved to capitalise on that new sense of immediacy, organising a series of events on Tuesday and this week to showcase the findings of the report, including a series of interviews with TV weather forecasters. "We want to emphasize to the public, this is not some distant problem of the future. This is a problem that is affecting Americans right now," Obama told NBC's Today show forecaster, Al Roker. "Whether it means increased flooding, greater vulnerability to drought, more severe wildfires — all these things are having an impact on Americans as we speak."

Environmental groups and Democratic members of Congress also rallied to support the report.

John Podesta, the White House counsellor, said Obama would rely on the report's findings as he moves ahead on the most ambitious phase of his climate change plan in June – a proposal to cut emissions from the current generation of power plants, responsible for nearly 40% of US carbon dioxide emissions.

The White House acknowledged Obama would continue to face strong pushback from Republicans and industry. Podesta said the most Obama could expect from Congress in the way of climate action was a modest energy efficiency bill.

Some Republican members of Congress continued to dismiss the findings of the report. Deb Fischer, a Republican Senator from Nebraska, attacked the science as "politically charged" and "far from settled" as well as Obama for bypassing Congress and using his executive authority to act on climate change.



Meanwhile, a leading coal industry lobby group, the American Coalition for Clean Coal Electricity, dismissed the report as “unsubstantiated scare tactics and hyperbole” and lashed out at Obama for moving ahead on power plant regulations.