End of the road for 'dirty' fuels – UN

A long awaited UN report on how to curb climate change says the world must rapidly move away from carbon intensive fuels, the BBC reports.

There must be a "massive shift" to renewable energy says the 33-page study released here in Berlin.

It has been finalized after a week of negotiations between scientists and government officials.

Natural gas is seen as a key bridge to move energy production away from oil and coal.

But there have been battles between participants over who will pay for this energy transition.

The Summary for Policymakers on mitigation paints a picture of a world with carbon emissions rising rapidly.

About half of all the carbon that humans have pumped into the atmosphere since 1750 has been emitted in the last 40 years.

Rates have been rising fast since 2000, despite the global economic crash.

The report points to an increased use of coal in the decade from the turn of the millennium , "reversing the longstanding trend of decarbonization of the world's energy supply".

Driven by a global increase in population and economic activity, global surface temperature increases will be between 3.7C and 4.8C in 2100 if no new action is taken.

This is way above the 2 degree level, regarded as the point beyond which dangerous impacts of climate change will be felt.

However, the scientists involved in the report say this situation can be turned around.

"It needs a big change in the energy sector, that is undoubtedly true," said Prof Jim Skea, one of the senior authors of the study.

"One of the biggest areas that's important is getting the carbon out of electricity, so renewable energy, nuclear, fossil fuels with carbon capture and storage, that's all part of the menu if we are going to make the transition to stay under the 2 degree target."

It is not a simple task. To be sure of staying below 2 degrees, the amount of carbon in the air needs to be around 450 parts per million by 2100. To get there, emissions in 2050 need to be 40-70% lower than they were in 2010.

The IPCC says that renewables are a critical part of that pathway.

Since the last report in 2007, the scientists say that renewable energy has come on in leaps and bounds.

In 2012, renewables accounted for just over half of the new electricity generation added around the world.

The scientists stress that renewables are becoming economically competitive with fossil fuels and also offer a range of other benefits, including clean air and energy security.

"It certainly is the end for carbon intensive fuels that's for sure," said Jennifer Morgan from the World Resources Institute, who was a review editor on one of the chapters of the IPCC report.

"There needs to be a massive shift away from fossil fuels and investment needs to shift to going 100% clean as fast as possible."

One of the surprising endorsements in the report is natural gas.

"Emissions from energy supply can be reduced significantly by replacing current world average coal-fired power plants with modern, highly efficient natural gas combined-cycle power plants," says the summary.

The report describes natural gas as a "bridge" technology with deployment increasing before peaking and falling below current levels by 2050.

However many of the scenarios examined by the panel would still involve an "overshoot" of the target range.

To cope with this the world may need to remove carbon from the atmosphere. Combining carbon capture and storage with bioenergy is seen as one potential solution, but the report is lukewarm on these ideas, saying the "methods are uncertain" and are "associated with risks".

Timing is everything, say the scientists.

"Delaying mitigation efforts beyond those in place today through 2030 is estimated to substantially increase the difficulty of the transition to low longer-term emissions," says the summary.