Global warming can be kept to about 2C if all nations honour the promises they made at the Glasgow climate summit but 1.5C is looking increasingly out of reach, a new study suggests.
Australian experts including University of Melbourne climate scientist Malte Meinshausen were part of the study in the journal Nature, along with European scientists from the International Energy Agency.
Associate Professor Meinshausen says it's a sobering mix of good and bad.
The good news is that for the first time, modelling has shown the world has an articulated pathway to keep climate change under 2C - but only just.
Everything will rest on all countries achieving - in full, and on time - stronger emissions reduction targets set at last year's COP26 climate summit in Glasgow.
If that happens, it's possible to keep warming to 1.9C to 2C, the study found.
The bad news is that's well beyond the primary objective of the Paris climate agreement to limit warming to well below 2C, preferably 1.5C.
Half of one degree might not sound like much, but the UN's Intergovernmental Panel on Climate Change says the difference will be profound for almost every ecosystem on earth.
The study found that even with the stronger targets, there was only a six per cent to 10 per cent chance of limiting warming to 1.5C and substantially more action was needed this decade to achieve that.
"There is some positive news because five years ago, we would never have thought that the pledges on the table would bring us to around 2C," Associate Professor Meinshausen said.
"Is it also a bad story? Yes, because the window for 1.5C is very rapidly closing, and the world will look very different at 2C."
He said the Australian government, which, had chosen not to join the push for accelerated action, despite what was on the line.
"Even 1.5C is not enough to save coral reefs from severe degradation. So the colourful beauty that we still have today is something that we should cherish, should visit, because it won't be around.
"Unfortunately for the Great Barrier Reef it's too late. There will be some remnant corals around, but it won't be the same beauty."
He said Australia's position was a great irony, given the impacts of climate change are already so visible, and that there was so much for the nation to gain economically from its bountiful renewable power sources.
United Nations secretary-general Antonio Guterres recently called Australia a "holdout" after Prime Minister Scott Morrison refused to strengthen the nation's 2030 emissions reduction target.
He also said it was still possible to keep the 1.5C goal alive but fossil fuel reliance had to end and the pace of transition to renewables needed to triple.
Mr Morrison has promised to achieve net zero emissions by 2050 under a plan that relies on a technology-led economic evolution to cut emissions, capture and store them, or offset them, while allowing coal and gas exports to continue as long as there is demand.
