11 Conclusion
Resolving the discrepancies between the methodology adopted by IPCC in AR4 and AR5 is vital. Once those discrepancies are corrected for, it appears that the impact of anthropogenic global warming over the next century, and
even as far as equilibrium many millennia hence, may be no more than one-third to one-half of IPCC’s current projections.
Suppose, for instance, that the equilibrium response to a CO2 doubling is, as the simple model credibly suggests it is, \1 K. Suppose also that the long-run CO2 fraction proves to be as high as 0.9. Again, this possibility is credible.
Finally, suppose that remaining affordably recoverable reserves of fossil fuels are as much as thrice those that have been recovered and consumed so far. Then, the total warming we shall cause by consuming all remaining
recoverable reserves will be little more than 2.2 K, and not the 12 K imagined by IPCC on the RCP 8.5 scenario. If so, the case for any intervention to mitigate CO2 emissions has not necessarily been made: for the 2.2 K equilibrium warming we project would take place only over many hundreds of years. Also, the disbenefits of more extreme heat may well be at least matched by the benefits of less extreme cold. It is no accident that 90 % of the world’s living species thrive in the warm, wet tropics, while only
1 % live at the cold, dry poles.
