IPCC March 2023
Stephen Salter
Hi All
While reducing atmospheric CO2 concentrations to net zero is desirable it is completely inadequate without effective time travel. The oceans now contain 40 times more CO2 than the atmosphere and this will come back out if atmospheric concentrations fall.
Releasing CO2 is like turning up a thermostat with a ratchet. There is a large thermal inertia so temperature rise is not immediate. There is an exponential rise towards some distant, higher value. James Hansen calculates the time-constant of this rise to two-thirds (strictly 1/e = 0.632) of its final value as about 40 years with the other third still to come. As well as this warming in the pipeline there are several quite powerful negative feedbacks, like the loss of arctic ice and methane release, which will accelerate the warming rate even with net-zero.
The political concentration on a safe limit of 1.5 C is in conflict with opinions of people in California, Pakistan and low-altitude islands who will argue that their present temperatures, droughts and rainfall are already too high. But simple mean values are a distraction. More important are the highs and lows either side of the mean and their durations. We recently had temperature anomalies of +6 C in Siberia and -12C in Texas.
You can get a useful model of the stability of a complicated system by thinking of a ball in a tray with an uneven surface of peaks, hollows and trenches, being shaken side-to-side. A ball in a hollow will roll up and down the sloped walls. The natural frequency of rolling will depend on the slope of the hollow walls.
But if something reduces the vertical dimensions of the tray, the natural frequency of rolling will slow down. This will increase the chance that the ball can move high enough up the slope to roll over a crest into an adjacent, different hollow and not return. This means that slower changes can be an early warning of approach to a permanent change.
As well as reducing emissions we have also got to do direct cooling. Several methods are possible. I have been working on the engineering of one of them, due to John Latham, to use the Twomey effect to increase the reflectivity of clouds. A reduction of the solar input of 0.5% would be sufficient to offset present CO2 levels. Hardware design is nearly complete. Please let me know if you would like more information.
Stephen
Emeritus Professor of Engineering Design
School of Engineering
University of Edinburgh
Mayfield Road
Edinburgh EH9 3DW
Scotland
0131 650 5704 or 0131 662 1180
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