[LE BOURGET] Emissions of carbon dioxide (CO2) from fossil fuels, the main driver of man-made climate change, are set to decline this year for the first time in a period of global economic growth, said a study on Monday.
The "surprising" findings were published as 195 nations entered the final phase of UN talks in Paris for an accord to roll back heat-trapping carbon emissions, blamed for dangerous climate change.
Thanks mainly to changes in China, the worldwide growth in emissions from fossil fuels-derived energy flattened in 2014 and is set to drop slightly - by about 0.6 per cent - this year, said the study in the journal Nature Climate Change.
The decline will come even though the global economy grew this year, by an expected 3.1 per cent, following expansion of 3.4 per cent in 2014, the authors noted.
"Unlike past periods with little or no emissions growth, global gross domestic product (GDP) grew substantially in both years," they wrote.
Previous periods of decline were temporary and have occurred during economic slowdowns, notably in 2009 after the global financial crisis.
Decoupling economic growth from emissions generated by oil, coal and gas is a key goal in the bid to tackle global warming.
Carbon-curbing strategies focus on improving energy efficiency from traditional fossil fuels and on shifting to low- or zero-carbon sources such as wind, solar, hydro, geothermal or nuclear.
The study was conducted by 70 scientists, led by Corinne Le Quere of the Tyndall Centre for Climate Research at the University of East Anglia in England.
Analysts who were not involved in the research hailed its signficance.
"The trend of rapid global emissions growth has been broken," said Michael Grubb at University College London.
"This keeps 2C in play," he added.
UN member nations have vowed to cap global warming to a maximum of two deg C above pre-Industrial Revolution levels.
However, the study cautioned that 2015 was unlikely to be the emissions "peak year" followed by a period of long-term decline.
"Energy needs for growing economies still rely primarily on coal, and emissions decreases in some industrial countries are still modest at best," said Le Quere.
"Even if emissions were to peak soon, global emissions would still take years to decline substantively," said the authors.
Greenhouse gases linger in the atmosphere for decades or even centuries, depending on their type.
The research team said their projection for 2015 fell within a range of statistical uncertainty, from a decline of 1.6 per cent to a small rise of 0.5 per cent.
National carbon-curbing pledges would slow runaway warming - projected to hit 4C or more - to about 3C, according multiple reviews.
But even at this level, humanity would be on a collision course with mass migration and increased poverty caused by rising seas, drought and violent storms.
The expected drop in 2015 was attributed largely to decreased coal use in China, the world's number one greenhouse gas emitter.
After rising nearly seven percent per year in the previous decade, China's emissions growth slowed to 1.2 per cent in 2014 and could be minus 3.9 per cent in 2015.
China's energy needs continue to expand rapidly. But nearly 60 per cent of the increase in primary energy use in the last two years was met by renewable and nuclear power.
CO2 emissions from the European Union have also declined by 2.4 per year in the past decade, and the United States by 1.4 per cent, said the authors.
A key contributor to projected future emissions is India, the study showed. More than 300 million Indians still do not yet have access to electricity.
"For global CO2 emissions to peak quickly, part of India's new energy needs must come from low-carbon technologies," the researchers wrote.
India has pledged - contingent on financial aid from rich countries - to generate 40 per cent of its electricity from renewable sources by 2030.
African countries are also confronted by a difficult choice as they seek to eradicate poverty, between abundant, cheap coal and pricier green technologies.
"A real wild card in future emissions is whether today's low-income economies lock in a high-carbon development path, or develop clean energy systems from the very beginning with the help of the advanced economies," commented Jim Williams, director of the Deep Decarbonisation Pathways Project.