A new paper is out in a special issue of Climate of the Past called Progress in paleoclimate modelling

It is from the ‘hockey team’ and titled “Using palaeo-climate comparisons to constrain future projections in CMIP5”. I loved this tweet from the LDEO Tree ring lab

Models agreeing with palaeoclimate give different future results than others

Gosh, who woulda thought that model output in tune with palaeoclimate data would be different than output from others? Last I heard, tree rings, corals, and cave limestone deposits aren’t climate forcings, so from my perspective, the claim is meaningless. And of course, the word “robust” is used in the abstract, which I think is Gavin’s favorite word. On the plus side, the paper is open access, so we can examine why they claim that.

See the paper and the abstract

Using palaeo-climate comparisons to constrain future projections in CMIP5, Clim. Past, 10, 221-250, doi:10.5194/cp-10-221-2014, 2014.

Schmidt, G. A., Annan, J. D., Bartlein, P. J., Cook, B. I., Guilyardi, E., Hargreaves, J. C., Harrison, S. P., Kageyama, M., LeGrande, A. N., Konecky, B., Lovejoy, S., Mann, M. E., Masson-Delmotte, V., Risi, C., Thompson, D., Timmermann, A., Tremblay, L.-B., and Yiou, P.:

Abstract. We present a selection of methodologies for using the palaeo-climate model component of the Coupled Model Intercomparison Project (Phase 5) (CMIP5) to attempt to constrain future climate projections using the same models. The constraints arise from measures of skill in hindcasting palaeo-climate changes from the present over three periods: the Last Glacial Maximum (LGM) (21 000 yr before present, ka), the mid-Holocene (MH) (6 ka) and the Last Millennium (LM) (850–1850 CE). The skill measures may be used to validate robust patterns of climate change across scenarios or to distinguish between models that have differing outcomes in future scenarios. We find that the multi-model ensemble of palaeo-simulations is adequate for addressing at least some of these issues. For example, selected benchmarks for the LGM and MH are correlated to the rank of future projections of precipitation/temperature or sea ice extent to indicate that models that produce the best agreement with palaeo-climate information give demonstrably different future results than the rest of the models. We also explore cases where comparisons are strongly dependent on uncertain forcing time series or show important non-stationarity, making direct inferences for the future problematic. Overall, we demonstrate that there is a strong potential for the palaeo-climate simulations to help inform the future projections and urge all the modelling groups to complete this subset of the CMIP5 runs.

Schmidt, G. A., Annan, J. D., Bartlein, P. J., Cook, B. I., Guilyardi, E., Hargreaves, J. C., Harrison, S. P., Kageyama, M., LeGrande, A. N., Konecky, B., Lovejoy, S., Mann, M. E., Masson-Delmotte, V., Risi, C., Thompson, D., Timmermann, A., Tremblay, L.-B., and Yiou, P.: Using palaeo-climate comparisons to constrain future projections in CMIP5, Clim. Past, 10, 221-250, doi:10.5194/cp-10-221-2014, 2014.

Paper PDF: http://www.clim-past.net/10/221/2014/cp-10-221-2014.pdf

From what I can make of the paper, it seems they are providing a road map to help modelers tune their model output to things like Mann’s hockey stick palaeo reconstructions, which they apparently still believe in even though the palaeo tree ring data showed a dive after 1960, which is why the whole “hide the decline” issue came about.

Not only was the deletion of post-1960 values not reported by IPCC, as Gavin Schmidt implies, it is not all that easy to notice that the Briffa reconstruction ends around 1960. As the figure is drawn, the 1960 endpoint of the Briffa reconstruction is located underneath other series; even an attentive reader easily missed the fact that no values are shown after 1960. The decline is not “hidden in plain view”; it is “hidden” plain and simple. Figure 3. Blowup of IPCC Figure 2-21.

Source: How “The Trick” was pulled off

I’m sure Steve McIntyre will weigh in on this new paper soon as he is best qualified to sort out what is “robust” in team science and what isn’t.

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