|IPCC delivers stark warning.
A UN-backed 'Intergovernmental Panel on Climate Change' has warned that fossil fuels must be phased out by 2100, if the world is to avoid dangerous climate change.
In an alarming report released earlier this week, it stated that most of the world's electricity can - and must - be produced from low-carbon sources by 2050.
If this target is not met then the planet is certain to face "drastic, inescapable and irreversible" damage.
The UN also warned that the potential consequences of inaction could be far costlier than taking the necessary action.
The IPCC's Synthesis Report was published on Sunday, following a week of intense debate between scientists and government officials in Copenhagen.
The research was undertaken to help inform politicians, currently engaged in attempts to deliver a new, cohesive, global treaty on climate by the end of 2015.
The report says that reducing emissions is crucial if global warming is to be limited to 2C - a target acknowledged in 2009 as the threshold of dangerous climate change.
The report also confirms that to achieve this target, renewable energy production needs to grow from 30% share to 80% of the power sector by 2050.
The report also states that in the longer term, fossil fuel power generation, without carbon capture and storage (CCS) technology, would need to be "phased out almost entirely by 2100".
Science has spoken
The Synthesis Report is effectively a summary of three previous IPCC reports, all of which outlined the causes, impacts and the potential solutions to climate change.
It re-states many familiar positions:
- Warming is "unequivocal" and the human influence on climate is clear
- The period from 1983 to 2012 was likely the warmest 30 year period of the last 1,400 years
- Warming impacts are already being seen around the globe, in the acidification of the oceans, the melting of arctic ice and poorer crop yields in many parts
- Without concerted action on carbon, temperatures will increase over the coming decades and could be almost 5C above pre-industrial levels by the end of this century
"Science has spoken," UN Secretary-General Ban Ki-moon said. "There is no ambiguity in their message. Leaders must act. Time is not on our side."
Ban Ki-moon: Inaction on climate change "will cost heavily"
"There is a myth that climate action will cost heavily," said Mr Ban, "but inaction will cost much more."
The US Secretary of State, John Kerry, described the report as "another canary in the coal mine".
"Those who choose to ignore or dispute the science so clearly laid out in this report do so at great risk for all of us and for our kids and grandkids," Mr Kerry said in a statement.
The Secretary of State for Energy and Climate Change Ed Davey described the report as the "most comprehensive, thorough and robust assessment of climate change ever produced".
"It sends a clear message that should be heard across the world - we must act on climate change now. It's now up to the politicians - we must safeguard the world for future generations by striking a new climate deal in Paris next year," he said.
"The UK has been leading the world and bringing the world with us. The historic agreement to cut carbon emissions in Europe by at least 40 per cent by 2030 effectively means our Climate Change Act is being replicated across Europe, just as it's being copied in countries across the world as they seek to cap and cut their own emissions."
Oxford University's Prof Myles Allen, a member of the IPCC research team, remarked: "We can't afford to burn all the fossil fuels we have without dealing with the waste product which is CO2 and without dumping it in the atmosphere."
"If we can't develop carbon capture we will have to stop using fossil fuels if we want to stop dangerous climate change."
David Shukman, BBC science editor commented;"The language in the UN's climate reports has been steadily ratcheted up over the years, but this publication lays out the options more bluntly than before.
The conclusion that fossil fuels cannot continue to be burned in the usual way - and must be phased out by the end of the century - presents governments with an unusually stark choice.
The IPCC has tried to make it more palatable by saying that fossil fuel use can continue if the carbon emissions are captured and stored.
But so far the world only has one commercially-operating plant of that type, in Canada, and progress developing the technology is far slower than many had hoped.
So this raises the difficult question of how key governments are likely to respond.
The report's clarity of language over the future of coal, oil, and gas was welcomed by campaigners.
"What they have said is that we must get to zero emissions, and that's new," said Samantha Smith from World Wildlife Fund.
"The second thing is they said that it is affordable, it is not going to cripple economies."