Roshanka Ranasinghe was one of just two Australians who worked as co-ordinating lead authors on the report, helped identify 33 so-called climate impact drivers (CID) and personally handled the Australasian assessment. He said that 26 of the highlighted impacts were broadly relevant for Australia.
“Of these 26, we have high confidence that 11 CIDs will change in all four Australian regions by mid-century under all [emissions] scenarios but the lowest ones,” Professor Ranasinghe, chair in climate change impacts and coastal risk at IHE Delft/University of Twente, told the Sydney Morning Herald and The Age. “This is consistent with the global warming level of about 2 degrees, relative to 1850-1900.”
These top 11 impacts included rising temperatures, extreme heat, ocean acidification and sea-level rise, which would get worse, while cold spells and frosts would decrease. “We also have high confidence that snow will decrease by mid-century,” he said.
“We are not just tracking whether temperatures are increasing, for example, but projecting when changes might reach critical tolerance thresholds for people, agriculture or wildlife,” Professor Ranasinghe added.
Worsening bushfire weather, worsening marine heatwaves that spell danger for our coral reefs, and lower winter rainfall for southern Australia are among the challenges to come.
The broader report presents a picture of the current state of the world’s climate and lays out five potential scenarios for future emissions pathways, ranging from low to high pollution trajectories. More detail will be coming in the next two IPCC instalments, particularly the third one on mitigation, due out next year.
However, regardless of what action the world takes now, warming over coming decades is locked in due to the amount of greenhouse gas emissions already in the atmosphere and the lagging effect they have on the climate, said one of the report’s lead authors, CSIRO’s Pep Canadell.
If the world immediately makes drastic cuts to emissions, and reaches net zero or carbon neutrality before 2050, the world can still stabilise the climate and see it slowly start to cool by the end of the century.
That achievement would require curbing emissions to about 500 billion tonnes in total, or about 12 years of current pollution levels, and even then there would be only a 50-50 chance of limiting warming to 1.5 degrees compared with pre-industrial times.
“It is not too late,” said Dr Canadell. “We are still in the control cabin of the planet and the climate system in determining the long-term future of climate.”
He said climate change was already part of the personal experience of humans enduring a wave of floods, heatwaves and fires as seen recently in China, Canada, Greece and in Australia in the past two months.
“Every decimal of a degree [of warming] that we are avoiding is a win for us and a win for the climate,” he said.
However, the report says many of the impacts of climate change, particularly changes in ocean warming and acidification, sea levels and ice sheets, are locked in for hundreds if not thousands of years unless massive extractions of atmospheric CO2 take place.
As well as likely scenarios, the report details climate changes that have a relatively low likelihood of occurring but could have potentially devastating impacts, such as the sudden disintegration of ice sheets or mass forest die-back, which it says cannot be ruled out from happening this century.
Formally titled Climate Change 2021: the Physical Science Basis, the report is the work of 234 scientists, is overseen by195 governments and involves reviews of 14,000 scientific papers. The final wording of the 40-page summary for policymakers was agreed in lengthy meetings in recent weeks that worked through the document word by word.
Since the first IPCC assessment report was completed in 1990, humans have emitted 1 trillion tonnes of carbon dioxide through burning fossil fuels or land clearing. That total is about 41 per cent of all that emitted since the industrial revolution in just three decades.
The report has a greater focus than previous assessments on non-carbon dioxide greenhouse gasses, such as methane, which it identifies as a significant contributor to warming.
This could lead to increased pressure on Australia due to the government’s support of a gas-led recovery and significant agricultural methane emissions.
For its part, the Australian federal government said climate change demanded a co-ordinated global response and its policies were designed to reach net zero emissions as soon as possible by driving down the cost of low-emissions technology, such as hydrogen to replace fossil fuels.
“The government is seeking to achieve net zero emissions as soon as possible,” Prime Minister Scott Morrison said in Parliament on Monday. “We’re seeking to do that by using technologies, not taxes.”
Energy and Emissions Reduction Minister Angus Taylor said the IPCC report highlighted the physical impacts of global warming and “overcoming these challenges is a shared responsibility”.
“Our technology-led approach to reducing emissions will see Australia continue to play its part in the global effort to combat climate change without compromising our economy or jobs,” Mr Taylor said.
Labor climate change and energy spokesman Chris Bowen argued the IPCC projections provided “yet more evidence of the costs of inaction” and said the “bare minimum” response from the federal government must be to set a deadline to reach net zero emissions.
Greens leader Adam Bandt said in light of the report a failure to lift Australia’s current goal of cutting greenhouse gas emissions to between 26 per cent and 28 per cent of 2005 levels would be “criminal negligence.”
The Greens are calling for net zero emissions to be reached in 2035, or ahead of the government’s “preference” to reach that point in 2050, and for a 75 per cent reduction by 2030.
With Mike Foley
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