Given China's emissions are roughly double the next largest polluter - the US - and triple the European Union's, its acceleration means there is a fast-diminishing chance that the rise in global average temperatures can be restricted to the range of 1.5 to 2 degrees, as agreed at the 2015 Paris climate conference.

"Most climate scientists think 2 degrees [compared with pre-industrial levels] to be aspirational," said Andy Pitman, director of the ARC Centre of Excellence for Climate Extremes.

Even if emissions ceased globally, it is probable warming would still reach at least 1.5 degrees given the longevity of carbon-dioxide and other heat-trapping gases in the atmosphere, he said.

With increasing evidence of extreme weather events even at the roughly 1 degree of warming so far - including compounding risks of bushfires, heatwaves and droughts - societies can expect impacts to worsen, Professor Pitman said: "The notion that 1.5 degrees is somehow safe is totally incompatible with the evidence."

'Not a pretty picture'

News in recent days that the Trump administration plans to bolster the ailing US coal-fired power industry by intervening in markets would worsen the global emissions picture.

The CSIRO's Dr Canadell said while US carbon emissions had fallen for a decade, last year's decline will likely be much smaller because of quickening economic growth at home and abroad.

The European Union, too, was likely to register a slower emissions drop. Australia, meanwhile, is on course to increase its carbon pollution for a fourth year in a row, a "remarkable" result for a rich nation, he said.

"If you put all the blocks together, it's not coming together as a pretty picture for 2018," Dr Canadell said.

Bill Hare, director of non-profit science think tank Climate Analytics, said the planet is currently on course for 3.4 degrees warming, although planned but as-yet unimplemented climate action could trim that to 3.1 degrees.

One cause for optimism includes the shift away from fossil fuels, which is speeding up because of tumbling prices for solar and wind.

"China is moving massively into renewables and electric vehicles, and despite some short term increase in coal use, this trend will continue," Mr Hare said.

Bruce Nilles, a former head of the Sierra Club's "Beyond Coal" campaign, who is visiting Australia, said President Trump's "brazen efforts" to help coal in US would likely be stymied by a flurry of lawsuits from other energy suppliers.

The US had seen 266 coal-fired power plants shut or set closure dates since 2010, and these "were continuing at the same rate as during the last few years of the Obama administration", he said.

Filling the gap were more than 10,000 megawatts of new wind and solar capacity each year, a process likely to continue as their technology becomes even cheaper, Mr Nilles said.