The report, more optimistic about curbing the use of fossil fuels than a Chinese industry forecast on Monday, noted that China's "coal consumption fell in 2014, and fell further in the first quarter of 2015".

"China's greenhouse gas emissions are unlikely to peak as late as 2030 - the upper limit set by President Xi Jinping in November 2014 - and are much more likely to peak by 2025," the report said.

"They could peak even earlier than that," write the authors Fergus Green and Nicholas Stern, both from the LSE's Grantham Research Institute on Climate Change and the Environment and the Centre for Climate Change Economics and Policy.

China, the top emitter of greenhouse gases - that are linked to rising ocean levels, heat waves and downpours - said last year its emissions would peak "around 2030, with the intention to try to peak early".

Wang Zhixuan, secretary general of the China Electricity Council, predicted in a research report on Monday that China's emissions from the power sector would keep rising to 2030, spurred by lower prices of coal than natural gas.

The industrial association projected that coal-fired power capacity would rise next decade, to 1,450 gigawatts in 2030 from 1,100 in 2020.

The LSE authors estimated that China's overall emissions could peak at the equivalent of between 12.5 and 14 billion tonnes of carbon dioxide a year by 2025, up from about 10 billion around 2012.

That earlier-than-expected high point would help the world get on track for limiting warming to a maximum of two degrees Celsius (3.6 Fahrenheit) above pre-industrial times, they wrote, as long as China introduced sweeping reforms from cities to public transport.

Group of Seven leaders were meeting in Germany on Monday to discuss issues including climate change and how to achieve the 2C target, which many experts say is fast slipping out of reach.

And senior negotiators from almost 200 governments are meeting from June 1-11 in the German city of Bonn to work on a U.N. deal due in Paris in December to limit temperatures.