The threat posed by climate change may be greater than previously thought, and global warming is advancing at an unsustainable rate, Prime Minister Tony Blair said in a report published Monday.

The government-commissioned report, titled "Avoiding Dangerous Climate Change," collates evidence presented at a conference on climate change hosted by Britain's Meteorological Office last year. It says scientists now have "greater clarity and reduced uncertainty" about the impacts of climate change.

In a foreword, Blair said it was clear that "the risks of climate change may well be greater than we thought."

[Chapters 2, 4 and 5 of the report, as well as Blair's foreword, were posted online in PDF form.]

"It is now plain that the emission of greenhouse gases, associated with industrialization and economic growth from a world population that has increased six-fold in 200 years, is causing global warming at a rate that is unsustainable," he wrote.

Over the next century, global warming is expected to raise ocean levels, intensify storms, spread disease to new areas and shift climate zones, possibly making farmlands drier and deserts wetter.

The U.N.-backed Intergovernmental Panel on Climate Change says temperatures rose by about 1 degree during the 20th century. Computer modeling predicts increases of between 2.5 degrees and 10.4 degrees by the year 2100, depending on how much is done to limit greenhouse gas emissions.

Scientists have warned of climatic "tipping points" such as the Greenland and West Antarctic ice sheets melting and the Gulf Stream shutting down.

In the British report, the head of the British Antarctic Survey, Chris Rapley, warned that the huge West Antarctic ice sheet may be starting to disintegrate, an event that could raise sea levels by 16 feet.

Rapley said a previous Intergovernmental Panel on Climate Change report playing down worries about the ice sheet's stability should be revised.

"The last IPCC report characterized Antarctica as a slumbering giant in terms of climate change," he wrote. "I would say it is now an awakened giant. There is real concern."

Blair's vow to put climate change at the center of the international agenda during Britain's leadership of the G-8 and the European Union last year met with limited success.

He was unable to overcome the Bush administration's antipathy to the Kyoto climate-change accord — rejected by the U.S. government on the grounds it would damage the economy.

British ministers also have acknowledged that Britain is unlikely to meet its own target of cutting carbon dioxide emissions by 20 percent by 2010.