A report by the Climate Council claiming that the global average temperature rise will likely breach 1.5C by the 2030s has caused division in the scientific community.
The report, published on Thursday, follows controversy over similar arguments made in a review by the Australian Academy of Science, which said global aspiration of limiting global heating to 1.5C was now “virtually impossible” to achieve.
In its report, the Climate Council says the majority of emissions cuts need to occur within the next decade to keep global heating to well below 2C and avoid major, irreversible tipping points.
It says Australia, to do its fair share, needs to effectively triple its emissions reduction target to 75% on 2005 levels by 2030 and achieve net-zero emissions by 2035.
The report does not argue that the long-term Paris goal is lost but says the global average temperature rise will likely overshoot 1.5C and will require drawdown – the removal of carbon from the atmosphere – to bring temperatures back down below this level.
“The science is telling us that global average temperature rise will likely exceed 1.5C during the 2030s, and that long-term stabilisation and warming at or below 1.5C will be extremely challenging,” the report says.
It says if temperatures spike above 1.5C for a significant period of time, ecosystems already affected by existing warming of 1.1C will become even more severely damaged.
“Climate-related damages will be widespread and could, in some settings, be an existential threat,” the report says.
Will Steffen, one of the report’s authors, said despite the fact that countries were already experiencing severe effects of climate change, every fraction of a degree by which further temperature rises could be limited mattered.
“Every 10th of a degree of avoided warming is very important for us,” he said.
He said keeping global heating well beneath 2C was achievable, particularly when major economies such as the US, China, the EU, the UK and Japan were strengthening their emissions reduction commitments.
Australia, by comparison, was being “rapidly left behind” as one of few countries without a net-zero emissions target.
The report’s analysis of the feasibility of limiting warming to 1.5C argues that multiple lines of evidence – including future warming that is locked into the system from emissions that have already occurred, current climate trajectories and the available global carbon budget – suggest this will be exceeded, at least temporarily.
The Climate Council said the report was peer-reviewed by Australian and international scientists.
“It is a case of putting these different lines together,” said Simon Bradshaw, another of the report’s authors and the Climate Council’s head of research.
“The whole point of pointing this out is to drive home the message of how urgent these emissions reductions are.”
It is the conclusion about 1.5C that has caused concern in some quarters of the scientific community.
The Climate Council made its report available to journalists under a strict embargo that included the condition that reporters not share the report with any external experts prior to publication.
Environmental groups were also asked to sign non-disclosure agreements before they received an advance copy of the report.
But climate scientists Carl-Friedrich Schleussner and Bill Hare obtained a leaked copy and have written an 11-page rebuttal to the report’s conclusions about the 1.5C goal.
Hare, who also questioned the Australian Academy of Science report that drew on Steffen’s work to make a similar finding, said the council’s overall conclusion about the urgency of rapid action on climate change in the next decade was correct.
But he said the council’s claim that countries can no longer limit global heating to 1.5C contradicted recent scientific reports, including by the United Nations Environment Programme and the Intergovernmental Panel on Climate Change.
“The claim that we can no longer limit warming to 1.5C is based on some fundamental scientific errors,” Hare said.
“Essentially, it is clear that the evidence presented in the Climate Council of Australia report does not support their claim that 1.5C will be exceeded.”
He said the report’s conclusion that carbon budgets showed countries couldn’t limit warming to 1.5C was especially problematic because there were uncertainties around the numbers.
“A recent paper by leading experts concluded there was 50% margin of error around carbon budget estimates,” Hare said.
However, Andy Pitman, a scientist at the Centre of Excellence for Climate Extremes at the University of New South Wales, said it was “a statement of fact” that temperatures would overshoot 1.5C and require technology to bring them back down.
“It’s simply not possible to limit warming to 1.5C now,” he said.
“There’s too much inertia in the system and even if you stopped greenhouse gas emissions today, you would still reach 1.5C [of heating].”
Monica Richter, of WWF Australia, said the feasibility of the 1.5C from a scientific point of view could not be a discussion that was “decoupled from the political and moral consequences of breaching 1.5C”.
“At its core, the possibility of limiting warming to below 1.5C remains an issue of politics rather than of science,” she said.
Bradshaw said while there was ongoing discussion in the scientific community, there was “absolute fundamental agreement on the task at hand, which is to get emissions to plummet”.