Greenhouse gas emissions should be cut to zero by the end of this century, with time running out to prevent the worst impacts of climate change.
That is the stark message of a new UN report which urges immediate action to keep global warming in check.
“If we continue business as usual, our opportunity to keep the temperature rise below two degrees centigrade will slip away within the next decade,” said UN Secretary-General Ban Ki-moon in Copenhagen, presenting the study by the Intergovernmental Panel on Climate Change.
“Even if emissions stopped tomorrow, we would be living with climate change for some time to come. The good news is that if we act now, immediately and decisively, we have the means to build a better and more sustainable world.”
The 40-page synthesis, summing up 5,000 pages of work by 800 scientists already published since September 2013, said global warming was now causing more heat extremes, downpours, acidifying the oceans and pushing up sea levels.
It points to options including energy efficiency, a shift from fossil fuels to wind or solar power, nuclear energy or coal-fired power plants where carbon dioxide is stripped from the exhaust fumes and buried underground. But carbon capture and storage (CCS) is expensive and little tested.
The study also says experts are at least 95 percent sure that man-made emissions of greenhouse gases, rather than natural variations in the climate, are the main cause of warming since 1950.
Approved by more than 120 governments, it will be the main handbook for negotiators of a UN deal to combat global warming due at a summit in Paris in December 2015.