Global warming is approaching the point of no return, after which widespread drought, crop failure and rising sea levels will be irreversible, an international climate change task force warned Monday.

It called on the Group of 8 (search) leading industrial nations to cut carbon emissions, double their research spending on technology and work with India and China to build on the Kyoto Protocol (search) for cuttings emissions of carbon dioxide and other "greenhouse gases" blamed for global warming.

The independent report was made by the Institute for Public Policy Research (search) in Britain, the Center for American Progress (search) in the United States and the Australia Institute (search).

"An ecological time bomb is ticking away," said Stephen Byers (search), who was co-chairman of the task force with U.S. Sen. Olympia Snowe (search), R-Maine. "World leaders need to recognize that climate change is the single most important long-term issue that the planet faces."

Byers is a close confidant of British Prime Minister Tony Blair (search), and the report was timed to coincide with Blair's commitment to advance international climate change policy during Britain's presidency of the G-8 this year.

Byers said it is vital that Blair secure U.S. cooperation in tackling climate change. President Bush has rejected the Kyoto accord, arguing that the carbon emission cuts it demands would damage the U.S. economy and that it leaves out emerging polluters like China and India.

"What we have got to do then is get the Americans as part of the G-8 to engage in international concerted effort to tackle global warming," said Byers. "If they refuse to do that then other countries will be reluctant to take any steps."

According to the report, urgent action is needed to stop the global average temperature rising by 2 degrees Celsius (3.6 degrees Fahrenheit) above the level of 1750 — the approximate start of the Industrial Revolution when mankind first started significantly adding carbon dioxide to the atmosphere.

Beyond such a rise, "the risks to human societies and ecosystems grow significantly," the report said, adding that there would be a danger of "abrupt, accelerated, or runaway climate change." It warned of "climatic tipping points" such as the Greenland and West Antarctic ice sheets melting and the Gulf Stream shutting down.

No accurate temperature readings were available for 1750, the report said, but since 1860 the global average temperature has risen by 0.8 percent to 15 degrees Celsius (59 degrees Fahrenheit).

The report said a 2-degree Celsius rise in the average temperature could be avoided by keeping the concentration of carbon dioxide in the atmosphere below 400 parts per million. Current concentrations of 379 parts per million "are likely to rise above 400 parts per million in coming decades and could rise far higher under a business-as-usual scenario," it said.

The task force urged G-8 countries to agree to generate a quarter of their electricity from renewable sources by 2025 and shift agricultural subsidies from food crops to biofuels.

The task force of senior politicians, scientists and business figures was formed last March. Its chief scientific adviser was Dr. Rajendra K. Pachauri, chairman of the United Nations' Intergovernmental Panel on Climate Change (search).

The British government welcomed the report, which mirrors many of the suggestions already floated by Blair in the leadup to Britain's G-8 presidency.

Blair has acknowledged the importance of U.S. cooperation, but concedes Washington is unlikely to sign on for the Kyoto Protocol and is instead pursuing international commitment to developing new environmentally friendly technology.