Harmful effects from global warming are already here and worsening, warns the first climate report from Barack Obama's presidency in the strongest language on climate change ever to come out of the White House.
Global warming has already caused more heavy downpours, the rise of temperatures and sea levels, rapidly retreating glaciers and altered river flows, according to the document released Tuesday by the White House science adviser and other top officials.
"There are in some cases already serious consequences," report co-author Anthony Janetos of the University of Maryland told The Associated Press. "This is not a theoretical thing that will happen 50 years from now. Things are happening now."
The White House document -- a climate status report required periodically by Congress -- contains no new research. But it paints a fuller, more cohesive and darker picture of global warming in the United States than previous studies and brief updates during the George W. Bush years. Bush was ultimately forced to issue a draft report last year by a lawsuit, and that document was the basis for this new one.
One adminstration official, Jane Lubchenco, called the new report a game changer that would inform policy but not dictate a particular solution.
"This report provides the concrete scientific information that says unequivocally that climate change is happening now and it's happening in our own backyards and it affects the kind of things people care about," Lubchenco said at a White House briefing. Her agency, the National Oceanic and Atmospheric Administration, was among the key contributors to the document.
The "major disruptions" already taking place will only increase as warming continues, the authors wrote. They project the average U.S. temperature could rise by as much as 11 degrees by the end of the century.
"Thresholds will be crossed, leading to large changes in climate and ecosystems," the study said in one of its key findings, adding that it could affect the survival of some species.
For example in the past few decades, winters in parts of the Midwest have warmed by several degrees and the time without frost has grown by a week, according to the report.
Shorter winters have some benefits, such as longer growing seasons, but those are changes that require adjustments just the same, the authors note.
"We're already seeing impacts across the nation," said co-author Virginia Burkett, coordinator of global change science at the U.S. Geological Survey. "The evidence is much stronger than it has been."
White House science adviser John Holdren said in a statement that the findings make the case for taking action to slow global warming -- both by reducing emissions and adapting to the changes that "are no longer avoidable."
"It tells us why remedial action is needed sooner rather than later," Holdren said.
Jerry Melillo, one of the report's authors, said at a White House briefing Tuesday afternoon that if action is taken soon to reduce heat-trapping gases, chances improve for avoiding some of the effects detailed in the report.
"There are a lot of things that are potentially possible if we don't bring climate change under control, and we would like to see them avoided," said Melillo, a biologist at the Marine Biological Laboratory in Woods Hole, Mass.
The report compiles years of scientific research and updates it with new data. It was produced by the interagency U.S. Global Change Research Program, relying on government, academic and research experts.
Water -- too much or too little -- is a dominant theme through much of the report, which says that resource will continue to be a major problem in every region of the country.
"Water permeates this document," Burkett said. She said the U.S. Southwest will get drier and hotter and that will be a crucial issue.
The nearly 200-page report has chapters examining the effects of global warming in each region -- from coastal zoning officials who must consider sea rise to Midwestern farmers recalculating their planting seasons.
Federal law requires comprehensive reports on global warming's effects every four years. An environmental group sued to force the Bush administration to issue an early draft of this report last summer because one had not been written since 2000. Since that time, the language has become stronger, but mostly because of fresher research, scientists said.
"The emphasis has shifted from just looking at the physical climate science to adapting to change," Burkett said in an interview.