Comments on the IPCC Special Report on 1.5degC

The IPCC report is available here http://www.ipcc.ch/report/sr15/ and the comments in the list below are not meant as an exhaustive and definitive list, but simply follow from a first reading. Others may decide there are other omissions or may disagree with those that we have made, in which case I welcome your comments.

1.       There is no estimate of an equilibrium sea level rise at 1.5 degC. This is a serious omission when paleoclimate records demonstrate that the last time we had 400ppm the sea level was 23 meters higher than today.

2.       There is no evidence that a 10 billion global population can be sustained if the temperature rises to 1.5degC. The observed crisis we have seen this year when the temperatures breached 1.16degC above baseline suggests that long term temperature rises of 1.5degC above baseline is inherently incompatible with sustaining a 10 billion population.

3.       The report assumes that if the temperature overshoots the 1.5degC target, it can be reversed, but this takes no account of irreversibility and hysteresis in the climate system due to such factors as sea ice loss, methane releases and increasing ocean heat content and is counter to the warning of irreversibility in AR5.

4.       The report gives little analysis on persistent upward pressure of CO2 emissions, yet its recommendation to avoid runaway climate change is to get to zero carbon by 2040. To put this in perspective, Schlumberger are currently expecting oil production to rise from 96 million barrels/day to 120 million barrels/day by 2020 and are gearing up accordingly.

5.       The best odds the report offers to avoid 1.5 degC in the event of obtaining zero carbon is only 66%. For something of such seriousness, a probability of 95% should be used.

6.       To have the best chance of limiting temperatures to 1.5degC, the report assumes methane emissions go to zero, but these are increasing exponentially in the critical Arctic regions.

7.       A key assumption in the report is that BECCS will reduce atmospheric CO2, but the report does not consider the thermal efficiency of BECCS power plants and simple calculations show that this can be no more than 7% once the energy for gas compression is included, and it will most likely be negative once the energy for separation is included, so it more likely that BECSS will add CO2 to the environment rather than remove it.

8.       There appears to be no consideration in the report of the rapid global temperature increases that have occurred over the last 12 months. 

9.       In the text of Chapter 2 of the report it states that “SSP-based modelling studies of mitigation pathways have identified high challenges to mitigation for worlds with a focus on domestic issues and regional security,” but the need for proactive security management has not made it into the Summary for Policy Makers (SPM) and is not being considered in policy responses.

10.   There does not seem to be any acknowledgment or consideration in the report that the extreme events of this year could be indicative of the climate now entering a condition of rapid and self-reinforcing transition from the habitable Holocene to uninhabitable Hot-house conditions.  If the concerns on the danger of interacting feedbacks mechanisms and a tendency towards super exponential change are valid, then the temperature spike of the last year cannot be dismissed as a short term anomaly and instead it should be considered as potentially strong evidence that rapid change is now underway.

11.   The implications of the logarithmic relationship between radiative forcing and CO2 concentration has not been considered in determining policy needed to stablise temperatures at 1.5degC. The effect of this relationship means that a 50ppm increase from 280 to 330 ppm increases radiative forcing by 0.88, but a 50ppm reduction from 450 to 400ppm reduces radiative forcing by only 0.68, thus once the initial warming has triggered amplification mechanisms then future hypothetical reductions in CO2 will be unable to provide an adequate cooling effect to offset the thermal inertia that will have built up.

12.   Despite Chapter 4 of the report indicating Solar Radiation Management (SRM) can be a useful contribution to climate change, the SPM rejects SRM and instead suggests that policy should be focused on carbon reduction and carbon removal even though all the available evidence strongly suggests that this cannot be done anywhere near fast enough to avoid initiating interacting climate change feedback mechanisms.