WGII climate risks overstated and invalid
Guest essay by Larry Hamlin
The UN IPCC AR5 WGII final climate report has been released. This UN WGII report attempts to evaluate various global risks associated with future climate change. The evaluation process utilized in the WGII report relies upon global temperature projections obtained from low and high CO2 emissions climate model scenarios that were developed and addressed in the UN IPCC AR5 WGI report which was released last year.
In the UN WGI AR5 report the climate models were shown to exaggerate and overstate projected increases in global temperatures based on CO2 levels assumed present in the atmosphere compared to actual observed global temperatures. This is extremely important given that the WGII report uses these exaggerated climate model higher global temperature projection scenarios to assess climate risks associated with increasing global CO2 levels.
Figure 11.25a from the UN AR5 WGI climate report showing how climate models exaggerate and overstate global temperature projections resulting from increasing atmospheric CO2 levels compared to observed global temperatures .
The UN AR5 WGII report utilizes these climate model exaggerated temperatures to define global risks associated with increasing CO2 levels resulting in greatly overstating future climate risks that are very likely invalid.
Thus the WGII report analysis overstates risks for given levels of atmospheric CO2 levels since as the report notes “Risks are reduced substantially under assumed scenarios with the lowest temperature projections compared to the highest temperature projections”.
The WGII report fails to mention or address that the AR5 WGI report showed that the CO2 driven temperature sensitivity of the earth based on actual global temperature observations is at the very lowest end of the low emissions climate model scenarios. This result reflects the consequence of the 15+ year long and growing global temperature pause which is never discussed in the UN WGII report.
This overriding AR5 WGI lower temperature CO2 atmospheric sensitivity result is simply concealed and ignored in the AR5 WGII final report which blithely goes on to make assessment after assessment of the impacts of increasing CO2 levels based on climate model temperature projections which have been shown to grossly exaggerate and overstate the global temperature increase impacts of atmospheric CO2 levels.
The climate model scenarios developed by the UN have other significant limitations beyond not being able to produce temperature projections that agree with measured global temperatures. These include that climate model temperature projections have no probabilities attached to their computed outcomes and that the resulting temperature projection outcomes are considered to be simply “plausible and illustrative”. Thus comparisons of climate model temperature outcomes to actually observed global temperatures is paramount to assessing whether these projections have validity.
The failure of the UN WGII report to utilize the results of the UN WGI report which showed that climate models grossly exaggerate and overstate global temperatures and then use these same flawed climate models to establish global temperature related risks associated with atmospheric CO2 levels means that the WGII claimed climate risk findings being both overstated and invalid.