An influential global panel of scientists declared today that global warming is "unequivocal", that its effects are likely to last for centuries, and that mankind is almost certainly to blame.

The Intergovernmental Panel on Climate Change - which draws together 2,500 scientists from more than 130 countries - issued its strongest warning on the consequences of warming as it published what is considered the most authoritative research yet on the issue.

While the IPCC’s previous assessment in 2001 rated the link between the warming planet and human behaviour as "likely", which is said to mean a probability rate of 66-90 per cent, this has now been revised to "very likely" - a greater than 90 per cent chance that mankind is to blame.

Sea levels will continue to rise for centuries along with temperatures, it found, because the process has already begun.

"Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations," the 20-page summary of the report read.

"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."

It added: "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level."

David Miliband, the Environment Secretary, described the report as a blow for "climate change deniers" and said it showed the urgent need for international political action.

"The report confirms our concerns that the window of opportunity to avoid dangerous climate change is closing more quickly than previously thought.

"It is another nail in the coffin of the climate change deniers and represents the most authoritative picture to date, showing that the debate over the science of climate change is well and truly over.

"What’s now urgently needed is the international political commitment to take action to avoid dangerous climate change. This has been absent so far."

The report predicted the average world temperature will rise by about three degrees by the end of the century.

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