Peter Fiekowsky
With intelligent scale-up, we expect to remove at least 30 Gt, which would compensate for continuing emissions. Then we have net-zero.Continuing at that rate, we will have restored pre-industrial CO2 levels by 2050.
I thought I'd run this through WTF to see what the model says about reducing CO2 concentration to 300ppm by 2050. WTF is intervention agnostic; it doesn't care how emissions are reduced or CO2 extracted from the atmosphere. Here's what it says would need to be done to get to 300ppm by 2050. Peter, is this feasible?
I've generously assumed that emissions will be gradually reduced to zero by 2070. On that basis, and assuming we start CDR in earnest this year and scale it along a logistic curve, we'd need to get to 125GtCO2yr-1 by 2035 and then gradually ramp it down to zero by 2070 to get to 300ppm by 2050. Here's the profile of emissions, CDR and net emissions, and then the trajectory of the reducing ppm. This scenario has warming peaking at about 1.7oC by 2030 and then settling at 0.5 oC by 2050.


You'll notice that the amount of CDR is substantially higher than the 30GtCO2yr-1 suggested by Peter. Perhaps he can explain how he gets to 300ppm with so little CDR.
WTF is a version of FaIR. It uses exactly the same calculations and parameters as FaIR except in relation to non-CO2 GHGs that have little relevance here (the way WTF accounts for non-CO2 GHGs is such that it produces virtually identical 2100 GSAT projections to FaIR for a wide range of SSP scenarios).
This is what WTF says would happen if you got to 30GtCO2yr-1 by 2030, held it there until 2070 and then gradually phased it out by 2170.


In this scenario we're at 434ppm in 2050 and don't get down to 300ppm until 2125. That might not be such a bad outcome but it's quite a long way from Peter's projections. It has very modest overshoot of the 1.5oC threshold and sees GSAT warming reducing steadily from a peak of about 1.8oC mid-century to settle around 0.5oC by 2150.
It is also worth noting that the businesses that would need to be created to deliver this scale of CDR would need to understand that it would be a short-lived bonanza. Having reached 300ppm, and assuming that emissions will have stopped long before then, the CDR will have to be terminated to prevent a human induced Ice Age. This has significant economic implications for the endeavour.
Robert
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