The countdown to climate-change catastrophe is to be spelt out by a task force of senior politicians, business leaders and academics on Monday.
In 10 years or less, they predict, the catastrophic point of no return may be reached.
The new study, Meeting the Climate Challenge, has been timed to coincide with British Prime Minister Tony Blair's promised efforts to advance climate change policy this year as head of both the G8 group of the world's richest nations and the European Union.
The report was assembled by the Institute for Public Policy Research in Britain, the Centre for American Progress in the US and the Australia Institute.
It says the danger point will be signalled when temperatures rise by two degrees Celsius above the average world temperature in 1750, before the industrial revolution.
The report says that global average temperature has already risen by 0.8C since then, so the world has little more than a single degree of temperature latitude before the crucial point is reached.
The consequences of such a rise could include widespread agricultural failure, water shortages and major droughts, increased disease, sea-level rise and the death of forests, according to the report.
"There is an ecological time bomb ticking away"
Stephen Byers, report co-chair
The researchers calculated the concentration of carbon dioxide in the atmosphere after which the two-degree rise will become inevitable, and say it will be 400 parts per million by volume (ppm) of CO2.
The current level is 379ppm, and rising by more than 2ppm annually - so it is likely that the 400ppm threshold will be crossed in just 10 years' time, the report adds.
"There is an ecological time bomb ticking away," said Stephen Byers, former British transport minister and a close Blair ally, who co-chaired the task force that produced the report with US Republican Senator Olympia Snowe.
The report urges all G8 countries to agree to generate a quarter of their electricity from renewable sources by 2025, and to double their research spending on low-carbon energy technologies by 2010.