Climate scientists will today attempt to regain public confidence in measures to control greenhouse gases with a crucial assessment of global warming.
The International Panel of Climate Change (IPCC) is expected to warn that it is now 95% certain that global temperatures are rising and that human activity is to blame.
It says carbon dioxide levels in the atmosphere will rise to double pre-industrial concentrations by the middle of this century, and that will result in a global temperature rise of between 1.5C (34.7F) and 4.5C (40.1F).
The report is a comprehensive analysis for policymakers, written and reviewed by some 900 scientists who looked at more than 9,000 studies on climate change.
Dr Richard Allan, a climate scientist at Reading University who contributed to the report, told Sky News that unless there is action to curb carbon emissions, they would cause serious changes to the planet's climate
"It would mean an increase in the frequency of hot extremes," he said.
"In 2003, there were extreme temperatures and a lot of people died in France. We can expect a lot more of these events because of warming.
"We can also expect marked changes in rainfall patterns, with impacts on agriculture."
The IPCC is under pressure from governments to explain why the rise in global surface temperatures has stalled over the last 15 years.
Sceptics argue it is evidence computer models of the climate are wrong.
But scientists counter that the planet warms in fits and starts. They point to evidence that an upwelling of cold water in the Pacific Ocean has absorbed heat from the atmosphere - but that is only temporary.
While scientists are increasingly confident in the evidence, some polls suggest the public is becoming less certain.
According to YouGov, the proportion of the public that believes human activity is making the world warmer has fallen from 55% in 2008 to 39% in 2013.
Over the same period there was a sharp rise in people who believe there has been no global warming - up from 7% to 28%.
Professor Chris Rapley, climate scientist at University College London, said the evidence is clear. Although the climate has always varied, human activity is accelerating the changes.
"This is unwelcome news so people want to shoot the messenger," he said.
"What people tend to do is look at some little piece of the jigsaw and say 'look this demonstrates that it's not real or it's not happening' and then they feel better because they don't have to worry about it.
"But the whole exercise that the IPCC is going through is to look at the whole picture and see the general patterns that emerge. It's the pattern in the reduction of snow and ice and increasing temperature that says there is something odd going on here."
