Friday, September 22, 2017

More on Millar et al.

Millar and Allen have an article in the Guardian explaining what their paper really says. They say that existing ESMs assume too little cumulative emissions by the 2020's when atmospheric carbon dioxide will be higher than now and so temperature higher than now. But we have already reached that level of cumulative emissions and so we need to do an adjustment to the graph of cumulative emissions vs temperature. But no change to the graph of temperature vs. current concentration of CO2. The discrepancy arises because of uncertainty in cumulative emissions. Models have backfilled this estimate from other variables. Then they say that human induced warming is 0.93C and so that is the temperature baseline of their shifted frame of reference:

The argument of critics like Gavin Schmidt, Zeke Hausfather, and me that the estimate of current human-induced warming is too low still stands. And this means that the remaining carbon budget is smaller than argued by Millar et al. Any likely path to 1.5 degrees will require exceeding that temperature and then bringing radiative forcing down again.

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