One of the reactions to Crok and Lewis was, e.g. by J.P. van Soest, (1) that we are already on the “business-as-usual”-scenario RCP8.5. But to my knowledge RCP8.5 (based on a low end SRES A2 scenario) was the worst case scenario of IPCC TAR. The A1B scenario was considered the business-as-usual scenario, also for KNMI’s Climate Challenge. (2) Also the current emission trajectory is more in line wirth A1B emissions than RCP8.5 emissions. (3) But the IPCC scenario’s are not only dependent on emission scenario’s, they are also dependent on sink modeling. Currently there is no sign of sink saturation which e.g. the Bern model assumes will happen this century. (4) We also see that Crok and Lewis are far more cautious than Lewis alone earlier. (5)
Combining all this knowledge we can arrive at a significant low temperature rise for the end of the century using the “business-as-usual” emission scenario A1B: 1.1 degree rise relative to 1990. (6)
(2) Climate Challenge:
(3) Emission comparison current, A1B, RCP8.5
(4) Comparison of Bern sink saturation, versus classic Fick diffusion
(5) Lewis’ low end equlibrium climate sensitivity estimate
(6) Modeling SRES A1B and A1T using Fick CO2 diffusion and 1.3 K/2xCO2.