In a boost for hopes to curb climate change, China's greenhouse gas emissions will probably peak in 2025, five years earlier than its stated target, a study said Monday.

On current trends, the world's biggest carbon emitter will discharge 12.5-14 billion tonnes of carbon dioxide equivalent (GtCO2e) in 2025, after which emissions will decline, it said.

The work was carried out by two research institutes at the London School of Economics (LSE).

"This finding suggests it is increasingly likely that the world will avoid global warming of more than two degrees Celsius above pre-industrial levels," they said in a statement.

The average temperature goal, which translates into 3.6 degrees Fahrenheit, is the upper limit targeted by the UN, which is seeking to enshrine it in a global accord in December.

"Analysing trends in the key emitting sectors, we conclude that 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," said the paper, co-authored by climate economist Nicholas Stern and analyst Fergus Green.

"They could peak even earlier than that."

The report pointed out that Chinese coal consumption fell in 2014 and in the first quarter of 2015, after years of growth that led to severe air pollution in its cities and massive emissions of greenhouse gases.

The researchers calculated that China's coal use has reached a "structural maximum" and should plateau over the next five years, while natural gas use grows rapidly.

This was caused by structural changes in the economy as well as government policies targeting more sustainable growth with a reduced environmental impact.

United Nations member states are gathered in Bonn until Friday to sculpt a world climate pact they have agreed to ink at the global conference in Paris.

- Chinese 'caution' -

The agreement, with the 2 C goal in mind, would enter into force in 2020, supported by a register of national greenhouse gas emissions curbs.

According to the UN's Intergovernmental Panel on Climate Change (IPCC), a 2 C pathway requires annual greenhouse gas cuts of 40-70 percent by 2050, compared to levels in 2010 -- and to zero or below by 2100.

"Whether the world can get onto that pathway (to 2 C) in the decade or more after 2020 depends in significant part on China's ability to reduce its emissions at a rapid rate post-peak..." said the new paper.

Current global emissions are about 50 GtCO2e, about a quarter by China alone, according to Green.

The paper said China's political culture may explain why its government "erred on the side of caution" in stating its objective of peaking emissions around 2030.