At the end of this month, the UN’s Intergovernmental Panel on Climate Change (IPCC) is scheduled to release the physical science basis of it Fifth Assessment Report on climate change. Between now and then, the final wording of its highly visible and influential Summary for Policymakers (SPM) will be hashed out in a meeting in Stockholm. The current draft version of the SPM has been “leaked” in order to drum up some media attention for the upcoming meeting/report.
Among many interesting statements in the draft SPM, this one particularly caught our eye:
[Climate] Models do not generally reproduce the observed reduction in surface warming trend over the last 10–15 years. There is medium confidence that this difference between models and observations is to a substantial degree caused by unpredictable climate variability, with possible contributions from inadequacies in the solar, volcanic, and aerosol forcings used by the models and, in some models, from too strong a response to increasing greenhouse-gas forcing. [italics in original, bold added by us]
We found this interesting because back in 2010, we, along with several co-authors, wrote a paper titled “Assessing the consistency between short-term global temperature trends in observations and climate model projections.” In that paper, we demonstrated that climate models do not generally reproduce the observed reduction in surface warming trend over the last 10-15 years. We also wrote that this was the result of some combination of inadequacies in the evolution of anthropogenic forcing (including aerosols), natural variability (both that which is captured and that which is insufficiently handled by climate models), as well as the strong possibility that climate models were producing too much warming for a given amount of greenhouse gas emissions.
Specifically, we wrote:
For most observational datasets of global average temperature, the trends from length 5 to 15 years lie along the lower tails of the probability distributions from the collection of climate model projections under the SRES A1B emissions scenario. Typically the probability of occurrence of the observed trend values lies between 5% and 20%, depending on the dataset and the trend length. In the HadCRU, RSS, and UAH observed datasets, the current value of trends of length 8, 12, and 13 years is expected from the models to occur with a probability of less than 1 in 20. Taken together, our results raise concern about the consistency between the observed evolution of global temperatures in recent years and the climate model projections of that evolution.
Possible reasons for why current trends are unusual when set among model projections include unknown errors in the observational temperature record, differences in the true vs. A1B-defined anthropogenic forcing changes, insufficiencies of the climate models to accurately replicate the characteristics of natural variability, inaccuracies in climate model transient climate evolution, and the overestimation by climate models of the actual climate sensitivity. These are in addition to the possibility that current trends represent simply a rare but not impossible situation that is generally captured by the climate models.
The IPCC’s take on the situation in the draft SPM sounds pretty much like what we concluded.
Notably, at the time of our paper, we were the only ones who were suggesting that the responsibility for the mismatch between observations and projections laid with the climate models. The two extant papers in the peer-reviewed scientific literature at the time (Easterling and Wehner, 2009; Knight et al., 2009) both concluded that the climate models (and their take on natural variability) could explain the observed slowdown (or in some cases, complete stoppage) in the rise of the earth’s average surface temperature during this recent period.
Our results arguing for climate model deficiencies forwarded the existing science in a way that the IPCC ultimately accepted.
In the time since we wrote our paper, several others have reached similar conclusions, most notably, the just-published paper in the prestigious journal Nature Climate Change by John Fyfe and colleagues (2013) titled “Overestimated global warming over the past 20 years” which concluded:
Recent observed global warming is significantly less than that simulated by climate models. This difference might be explained by some combination of errors in external forcing, model response and internal climate variability.
Now for the rest of the story.
Our paper was repeatedly rejected by the scientific journals and consequently was never published in the form of a peer-reviewed article.
The reviewers were horrified that we characterized the mismatch between the observations and the model projections as being a “cause for concern” regarding climate model performance.
Now, three years later, the possibility that the models are to blame is so well accepted that it is included in the Summary for Policymakers (or at least the leaked draft) of the new IPCC report.
It is our hunch (see Section VIII) that the reason our paper was rejected was not (as we can now see) that it was wrong, but instead was because of who we are.
[Note: The details of the findings in our rejected manuscript were presented at Third Santa Fe Conference on Global and Regional Climate Change in November 2011, and the major results presented to the 2013 American Geophysical Union’s Science Policy Conference in Washington DC this June.]
References:
Easterling, D. R., and M. F. Wehner (2009), Is the climate warming or cooling? Geophysical Research Letters, 36, L08706, doi:10.1029/2009GL037810.
Fyfe, J., N.P. Gillett, and F.W. Zwiers, 2013. Overestimated global warming over the past 20 years. Nature Climate Change, 767-769.
Knappenberger, P.C., and P.J. Michaels, 2013. Policy Implications of Climate Models on the Verge of Failure. American Geophysical Union Science Policy Conference. Washington, DC, June 24-26, 2013.
Knappenberger, P.C., Michaels, P.J., Christy, J.R., Liljegren, L.M., Herman, C.S., and J.D. Annan, 2011. Assessing the consistency between short-term global temperature trends in observations and climate model projections. Third Santa Fe Conference on Global and Regional Climate Change, Santa Fe, NM, October 30-November 4, 2011.
Knight, J., Kennedy, J. J., Folland, C., Harris, G., Jones, G. S., Palmer, M., Parker, D., Scaife, A., & Stott, P. (2009), Do global temperature trends over the last decade falsify climate predictions? In: Peterson, T. C., & Baringer, M.O. (eds), “State of the Climate in 2008” Special Supplement to the Bulletin of the American Meteorological Society, 90-91.