‘How lucky do you feel?’: The awful risks buried in the IPCC report

The IPCC’s language, too, doesn’t necessarily convey the nature of the threat, much of which will be detailed in the second AR6 report on the impacts of climate change, scheduled for release next February.

“Like just stating the AMOC collapse by 2100 is ‘very unlikely’ – that was in a previous report – it sounds reassuring,” Professor Rahmstorf said. “Now the IPCC says they have ‘medium confidence’ that it won’t happen by 2100, whatever that means.”

West Antarctic melt

Another potential tipping point is the possible disintegration of the West Antarctic ice sheet. Much of the sheet lies below sea level and as the Southern Ocean warms, it will melt causing it to “flow” towards the sea in a process that is expected to be self-sustaining.

This so-called marine ice sheet instability is identified in the IPCC report as likely resulting in ice mass loss under all emissions scenarios. There is also “deep uncertainty in projections for above 3 degrees of warming”, the report states.

Containing enough water to lift sea levels by 3.3 metres, it matters what happens to the ice sheet. As Andrew Mackintosh, an ice expert at Monash University, says, the understanding is limited: “We know more about the surface of Mars than the ice sheet bed under the ice.”

Permafrost not so permanent

Much has been made about the so-called “methane bomb” sitting under the permafrost in the northern hemisphere. As the Arctic has warmed at more than twice the pace of the globe overall, with heatwaves of increasing intensity and duration, it is not surprising that the IPCC has listed the release of so-called biogenic emissions from permafrost thaw as among potential tipping points.

These emissions could total up to 240 gigatonnes of CO2-equivalent which, if released, would add an unwanted warming boost.

The IPCC lists as “high” the probability of such releases during this century, adding there is “high confidence” that the process is irreversible at century scales.

Other risks

From the Amazon rainforest to the boreal forests of Russia and Canada, there is a risk of fire and pests that could trigger dieback and transform those regions.

Australia’s bush faces an increased risk of bad fire weather days right across the continent, the IPCC notes. How droughts, heatwaves and heavy rain and other extreme events will play out at a local level is also not well understood.

Ocean acidification and marine heatwaves also mean the world’s coral reefs will be much diminished at more than 1.5 degrees of warming. “You can kiss it goodbye as we know it,” says Sarah Perkins-Kirkpatrick, a climate researcher at the University of NSW, said.

Global monsoons, which affect billions of people including those on the Indian subcontinent, are likely to increase their rainfall in most parts of the world, the IPCC said.

Andy Pitman, director of the ARC Centre of Excellence for Climate Extremes, said policymakers need to understand that much is riding on these tipping points not being triggered as even one or two of them would have long-lasting and significant effects. “How lucky do you feel?” Professor Pitman says.

Biggest uncertainty

Christian Jakob, a Monash University climate researcher, said that while there remain important uncertainties, science is honing most of those risks down.

Much harder to gauge, though, is which emissions path humans are going to take. Picking between the five scenarios ranging from low to high that we are going to choose is “much larger than the uncertainty we have in the science,” Professor Jakob said.