Using their strongest language to date, a group of the world's leading climate scientists say that global warming has already started, is "very likely" caused by man and will be unstoppable for centuries.

According to a copy of the report obtained by The Associated Press, the Intergovernmental Panel on Climate Change — a group of hundreds of scientists and representatives of 113 governments — warned that the world has already begun to warm and that hotter temperatures and rising sea levels will continue for "centuries" regardless of how much humans control pollution.

"The observed widespread warming of the atmosphere and ocean, together with ice-mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that is not due to known natural causes alone," said the report, which also linked recent increases in stronger hurricanes to global warming.

The associate director of the Office of Science and Technology Policy at the White House, Sharon Hays, praised the strong language of the report — considered the most authoritative science on global warming to date — telling the AP, "It's a significant report. It will be valuable to policy makers." She stopped short of saying how or whether it could bring about change in President Bush's continued rejection of calls for mandatory limits on greenhouse gas emissions. The report comes one week after Bush made his first reference to "global climate change" during his recent State of the Union address (see "President Bush Pleads For War Support In State Of The Union Address").

The use of the phrase "very likely" in the report translates into a more than 90 percent certainty that global warming is caused by human's burning of fossil fuels, the AP reported, which presents the strongest conclusion to date on the issue and practically eliminates the ability to say that natural forces are to blame.

Though it was a step up from the conclusion in the panel's previous report in 2001 — which said warming was "likely" caused by human activity — the group did not go a step further as some had speculated and use the phrase "virtually certain," which would translate to 99 percent certainty.

Among the panel's predictions were that temperatures would rise somewhere in the range of 2 to 11.5 degrees Fahrenheit by the year 2100, though its best estimate was for temperature rises of 3.2 to 7.1 degrees Fahrenheit. It also projected that sea levels would rise 7 to 23 inches by the end of the century, with an additional 3.9 to 7.8-inch increase if recent, unexpected melting of polar ice sheets continues.

If there was a silver lining, it was that some, but not all, of the projected temperature and sea-level rises are slightly lower than projected in the 2001 report, mostly due to the use of more likely, though still potentially devastating, scenarios. The report was based on years of heavily reviewed research and it was edited by governments with an eye toward the required unanimous approval by world governments.

The panel will release the second of the four phases of its report in April, when it will discuss the effects of global warming.

For more on climate change, check out the MTV Think feature "Break the Addiction: An Inconvenient Truth."