Peter Lilley and Graham Stringer voted against the Energy and Climate Change Select Committee’s report on the Inter-governmental Panel on Climate Change Fifth Report because “we believe the role of the Select Committee is to hold public institutions critically to account not to act as their cheer leaders”.
They added: “As scientists by training, we do not dispute the science of the greenhouse effect – nor did any of our witnesses. However, there remain great uncertainties about how much warming a given increase in greenhouse gases will cause, how much damage any temperature increase will cause and the best balance between adaptation to versus prevention of global warming.
The bulk of the main IPCC technical report recognises these uncertainties and is simply a useful compilation of the research in the field.
However, the Summary for Policy Makers is far less balanced than the report it purports to summarise.
Its headline conclusion was that “evidence for human influence has grown since AR4. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century”. It is hard to justify that increase in confidence that CO2 emissions are dominant given that: about one third of all the CO2 omitted by mankind since the industrial revolution has been put into the atmosphere since 1997; yet there has been no statistically significant increase in the mean global temperature since then. By definition, a period with record emissions but no warming cannot provide evidence that emissions are the dominant cause of warming!
The pause in surface warming does not invalidate the greenhouse effect. But it does mean that other factors – natural variations – can be of the same magnitude as the greenhouse effect over at least a decade and a half. Since such variations are presumed to cancel out over the long term variations in the opposite direction may have contributed a significant portion of the surface warming over the previous two and a half decades.
The IPCC’s conclusion flies in the face of the Inter Academy Council Review on the previous IPCC report which criticised its “authors [who] reported high confidence in some statements for which there is little evidence” and recommended that “Quantitative probabilities (as in the likelihood scale) should be used to describe the probability of well-defined outcomes only when there is sufficient evidence. Authors should indicate the basis for assigning a probability to an outcome or event (e.g., based on measurement, expert judgment, and/or model runs)”. No such basis for assigning this enhanced probability was given even though it is the headline conclusion of this report.
Moreover, the Summary for Policy Makers systematically omits mentioning or plays down key information in the main report which might suggest that the problem of global warming may be less acute or less certain than previously suggested. Notably it omits to alert Policy Makers to the following facts:
1. The IPCC’s medium term forecast for temperature to 2035 is below that given by the climate models since the experts believe these to be “overheating”. However, the forecast to the end of the century assumes the temperature will revert to following the projections of the models with no allowance for their tendency to exaggerate warming.
2. New estimates of the impact of aerosols based on satellite observations are both more certain and suggest a smaller cooling effect than previously assumed. However, there was not time to rerun the models using these latest aerosol figures. They will, however, inevitably mean that the models are even more out of line with temperature data than previously thought. This was described by one of our witnesses as “”the most significant thing in AR5 because if aerosol cooling is lower and … we know how much warming there has been, then it must follow … a much lower figure [is] attributable to carbon dioxide”.
3. For the first time the IPCC authors cannot agree on a best estimate for climate sensitivity even though they did in previous reports. There is only a cryptic reference to this in a footnote in the SPM. It is hard to square this unprecedented disagreement between the experts with the stated increase in their confidence in the scale of global warming.
4. Most recent empirically based studies suggest that the sensitivity of the climate to increases in CO2 is probably lower than assumed in the climate models.
5. The pause in global warming since 1997 may well be the result of natural variations offsetting the warming effect of more CO2 in the atmosphere. But if that is the case it follows that natural variations may have contributed a sizeable proportion of the warming in the 25 years prior to 1997.
6. Over the last 35 years (not just during the hiatus) the composite of models followed by the IPCC have collectively run 15% too high.
7. Forecasts of global warming generated by climate models have progressively converged on each other but diverged from actual observations of mean global surface temperature.
These issues were raised during the Committee’s inquiry. It is unfortunate that they were not dealt with in the Committee’s report. The Committee’s report would have been more balanced if it had drawn a distinction between the largely technical main Report and the much more politicised Summary for Policy Makers.
Graham Stringer MP and Rt Hon Peter Lilley MP
Members of Select Committee on Energy and Climate Change
Peter Lilley firstname.lastname@example.org
Graham Stringer email@example.com