As leaders of the Group of Eight industrial nations prepare to meet in Scotland -- with climate change and Africa at the top of the agenda -- a statement by the national science academies of 11 countries said: "It is likely that most of the warming in recent decades can be attributed to human activities.
"The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action," said the statement from the science academies of the G8 nations as well as China, India and Brazil.
While most scientists agree the burning of fossil fuels for transport and to generate electricity is a major contributor to potentially catastrophic climate change, the United States under President George W. Bush is unconvinced.
British Prime Minister Tony Blair has made tackling global warming, with its rising sea levels, increases in droughts and floods and threats to the lives of millions of the world's poorest people, a key goal of his 2005 presidency of the G8.
"It is clear that world leaders, including the G8, can no longer use uncertainty about aspects of climate change as an excuse for not taking urgent action to cut greenhouse gas emissions," said Lord May, head of Britain's Royal Society national science academy.
He called US policy "misguided" and noted that crucial to the international acceptance of the statement was the fact that leading scientists from three of the world's biggest developing world emitters China, India and Brazil had also signed it.
SILENCE ON TARGETS
Blair has called for global action to cut emissions of so-called greenhouse gases like carbon dioxide and insisted on a programme of action to emerge from the G8 summit at Gleneagles, some 65 km (40 miles) from Edinburgh, on July 6-8.
But a leaked draft last month of the climate change declaration due from the summit was silent on the science and contained neither targets nor timetables.
The national science academies likewise avoided talk of targets, calling instead for "cost-effective steps" to cut greenhouse gas emissions and noting that any delays would increase the problems and therefore the costs.
But they also noted the potentially devastating impact of global warming on the poorest nations which lacked the money or infrastructure to cope with anticipated crop failures and water shortages, and called for international action to help.
Environment group Friends of the Earth welcomed the increased pressure the science statement would put on the G8 leaders but lamented the lack of concrete goals.
"G8 countries must accept their historic responsibility in creating the problem, and show genuine leadership through annual reductions in emissions," campaigner Catherine Pearce said.
"It is crucial that the entire world -- including the United States -- recognises that there is a window of opportunity to avert potentially catastrophic climate change. Emissions must peak and decline within the next decade. The world must act now before it is too late," she added.