“It is clear that climate change is happening now. The observed climate changes we report are not opinions to be debated. They are facts to be dealt with,” he said.
The nearly 200-page document is a joint venture between the White House and 13 federal agencies.
It has been released as the US Congress considers legislation that imposes the first national cap on emissions while also seeking to reduce them.
Mr Obama’s chief science adviser, John Holdren, says action must be taken.
“Action needs to include both measures to reduce the emissions of heat-trapping pollution that are driving this problem and measures to adapt to the part of climate change we can’t avoid,” he said.
The report compiles years of scientific research and updates it with new data, painting a bleaker picture of global warming in the United States than has been done before.
It reveals that the average temperature in the US has risen 2 degrees Fahrenheit over the past 50 years, and might rise by up to 11 degrees Fahrenheit by the year 2100.
It warns the number of deaths from heat waves could double in Los Angeles and quadruple in Chicago if emissions are not reduced.
Sea levels are also expected to rise, with the area near New York City one of the worst hit.
The National Oceanic and Atmospheric Administration’s Jane Lubchenco says humans are to blame.
“We’re also reporting today with greater confidence than ever before that human activities are the main cause of the changes we see underway,” she said.
“I really believe this report is a game changer, I think that much of the foot dragging in addressing climate change is a reflection of the perception that climate change is way down the road, it’s in the future.
“And this report demonstrates, provides the concrete scientific information, that says unequivocally that climate change is happening now.”
Meanwhile the United Nations is warning of what it calls “megadisasters” in the world’s biggest cities unless more is done to heed the threat of climate change.
It says tens of millions of people are highly exposed because they live in big cities that would be threatened by rising sea levels or earthquakes.
And a new report from the Red Cross likens forecasting the impact of global warming to rolling a dice saying: “confronted with global warming, we know the dice is loaded”.