Global temperature rises could breach the critical 1.5-degree threshold in the early 2030s, the world's top climate scientists have warned in a landmark new report.
The UN Intergovernmental Panel on Climate Change's (IPCC) latest report says that without "immediate, rapid and large-scale" cuts to record high levels of greenhouse gas emissions then hopes of containing global warming to even 2 degrees would be "beyond reach".
Longer heatwaves, more frequent droughts and other extreme weather events, as well as rising sea levels, would be among the consequences of failing to suppress average temperature rises to below the Paris targets.
The panel's vice chair and Australian National University professor Mark Howden told The Canberra Times that while it was still possible to keep global warming below 1.5 degrees, it would require quick, strong and sustained action to cut emissions.
"The ball's in our court," he said.
The IPCC's report, published on Monday, will put further pressure on the Morrison government to set more ambitious short and long-term climate action targets.
The study - which draws on the expertise of more than 200 experts, including from Australia - is the first major update since the panel's 2018 report examining the prospects of 1.5 degrees of global warming.
The 2018 report predicted global warming would reach 1.5 degrees between 2030 and 2052 if temperature rises continued at its current pace.
The new study provides updated projections on when the threshold might be crossed, along with a warning to policy makers about the consequences of inaction.
The scientists examined five scenarios, which modelled potential global temperature rises under varying rates greenhouse gas emissions.
Significantly, the 1.5-degree Celsius mark was expected to be reached or exceeded before 2040 under all five scenarios.
The planet's so-called "carbon budget" - the amount that can be emitted before the 1.5 mark is reached - could be expended within 12 years if current rates of emissions continue.
Under the highest polluting scenario, it was "very likely" that temperature rise would approach 2 degrees in the next two decades and reach as high as 5.7 degrees by 2100.
The low emissions scenario, which assumes net zero is achieved around 2050 and carbon dioxide is removed from the atmosphere, could see average temperatures drop below 1.5 degrees of pre-industrial levels towards the back end of this century.
The Paris targets aim to limit global warming to "well below" 2 degrees, and preferably to 1.5 degrees, compared to pre-industrial levels.
Prof Howden, who is director of the ANU Institute for Climate, Energy and Disaster Solutions, said the "most likely" scenario was that the 1.5-degree mark would be breached.
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But he said average global temperatures could be brought back down over time if policy makers elected to pursue the low emissions pathway.
"If we don't start to reduce our emissions significantly before 2050, the world is extremely likely to exceed 2 degrees celsius of warming during the 21st century," he said.
"Reducing emissions from the 2020s onwards and reaching net-zero before the 2050s is really our best chance at keeping temperature increases below 1.5 degrees."
While experts predict that a 1.5-degree temperature rise could be recorded in a 12-month period this decade, the threshold will only officially be crossed once that is the average across a 20-year period.
Another IPCC report author, Pep Canadell, warned that there was "no bottom end to how much damage we can create", as he stressed that each fraction of temperature rise which could be avoided was a "win for us and a win for the planet."
"We need to make clear that we are still in control of the planet and the climate system in determining the long-term future of climate," he said.
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