Another prof says “it’s difficult to see how we could accommodate 8 billion people or maybe even half that . . . it will be a turbulent, conflict-ridden world”.
Among other impacts, the authors say, 4 degrees would in the long run melt both polar ice caps, with a sea-level rise of about 70 metres. Even 3 degrees would be catastrophic and make some nations, and regions, unliveable.
The authors say most people don’t understand what “global mean [average] warming” implies. As a general rule, global average warming of 4 degrees – covering land and ocean – is consistent with 6 degrees over land (that is, warming over the ocean would be a lot lower, bringing the average down) and with average warming of 8 degrees over land in the mid-latitudes.
That, in turn, risks an average warming of 10 degrees in summer. Or perhaps 12 degrees during heatwaves. All this is packed inside a tolerable-sounding global annual average warming of 4 degrees.
The authors say that Western Sydney has already reached heatwaves of 48 degrees. Add 12 degrees to that and you get summer heatwaves of 60 degrees. Phew.
Now, remember that psychologists and communications experts have been warning climate change campaigners that, if they make their message too frightening, the reaction of many people won’t be to rush out and join Extinction Rebellion, but to close their ears and do nothing.
Remember, too, that the modelling and projections of the climate scientists are far from certain sure and, as with the virus modelling of the epidemiologists, are based on assumptions that keep changing as our understanding of the phenomenon improves.
For these reasons, the UN’s Intergovernmental Panel on Climate Change has long erred on the side of understatement. But the risk with all this is that sensible people with the best intentions – such as regulators of the financial system – don’t realise how bad things could get.
The authors of Degrees of Risk say the science of climate change is inherently complex because it describes the dynamics of a multi-dimensional, “non-linear” system, involving many sub-systems and networks of adverse “cascade effects”.
‘In a period of rapid warming, most major tipping points, once crossed, are irreversible on human time frames.’
Degrees of Risk report
“Some responses to increasing levels of greenhouse gases are relatively linear and able to be projected well by climate models” but other responses are “non-linear, characterised by sudden changes, rather than smooth progress, which take the system from one discrete state to another, possibly with system cascades” where one change touches off a chain of changes.
“Factors contributing to this non-linearity include the existence of tipping points – polar ice sheets [melting], for example – where a threshold exists beyond which large, system-level change will be initiated, and positive feedbacks [that is, self-reinforcing loops] drive further change.
“In a period of rapid warming, most major tipping points, once crossed, are irreversible on human time frames”.
The authors’ message to regulators of the financial system is that the risk to banks and businesses at degrees of warming of anything like 3 or 4 degrees are huge, but so uncertain as to be unmeasurable. We need to act on the precautionary principle of significantly reducing emissions now, so we never get to find out how bad it could be.
The more prosaic message I draw is that we mustn’t kid ourselves that climate change is just another problem with unpopular solutions that we’ll muddle through as we always do.
Ross Gittins is the economics editor.
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