Purveyors of climate doubt have seized on a news release from the Research Council of Norway with this provocative title: "Global warming less extreme than feared?" The release describes new research finding that global warming from the buildup of greenhouse gases will be on the low end of the persistently wide spread of projections by other research groups. (There's a presentation describing the work below.)
This may well end up being the case (I'd give it higher than even odds; even so, that doen't justify an "all clear" alert). But this particular analysis has, as yet, not been published in a peer-reviewed journal. This means that although the release comes from a prestigious government science agency, the work needs a publicity before publication caution label. I created one just for this purpose (above) and will use it when needed.
This is hardly the first instance of a promotion-before-review approach to climate discourse. For instance, Richard Muller's Berkeley Earth Surface Temperature project took this path (one of that group's five papers has finally made it into a journal). (This phenomenon is not limited to climate science, of course; here's an example related to the fight over gas drilling.)
Earlier today I sent the following query to the Research Council of Norway and I'll update this post when I hear more:
With some urgency I'm trying to get some clarity on the status of the climate sensitivity analysis that the Research Council promoted yesterday. Is it published in a peer-reviewed journal? The only relevant study I could find was published last year (see below).
Perhaps it's more like a U.S. National Academy report? If so, please describe the level of peer review. The work is being aggressively disseminated by bloggers and news outlets that focus on any research casting doubt on the importance of greenhouse-driven warming.
Thanks for any input clarifying the status of the research and explaining why it was released now if it's not yet accepted for publication?
I included a link to a presentation on the paper (which you can read below) and to this relevant paper from last year:
Bayesian estimation of climate sensitivity based on a simple climate model fitted to observations of hemispheric temperatures and global ocean heat content
Magne Aldrin, Marit Holden, Peter Guttorp, Ragnhild Bieltvedt Skeie, Gunnar Myhre, Terje Koren Berntsen
Here's a presentation about the new analysis of global warming (the closest thing I've seen to the paper itself):
Norwegian Study Finds Limited Warming from Doubled Greenhouse Gases by Andrew Revkin
Finally, for those who want to dig in a bit, here's a comment I received from Reto Knutti, a Swiss climate scientist, after I sent the Norwegian release and presentation around:
As you said, Aldrin et al. (DOI: 10.1002/env.2140) is published, whereas Skeie et al. is not yet as far as I know. But here are some thoughts that are largely independent of this paper to put these types of studies in context.
If you look at the Fig. 3a in our review (red lines at the top) you see that many previous estimates based on the observed warming/ocean heat uptake had a tendency to peak at values below 3°C (that review is from 2008). The Norwegian study is just another one of these studies looking at the global energy budget. The first ones go back more than a decade, so the idea is hardly new. The idea is always the same: if you assume a distribution for the observed warming, the ocean heat uptake, and the radiative forcing, then you can derive a distribution for climate sensitivity.
What is obvious is that including the data of the past few years pushes the estimates of climate sensitivity downward, because there was little warming over the past decade despite a larger greenhouse gas forcing. Also in some datasets the ocean warming in the top 700 meters is rather small, with very small uncertainties (Levitus GRL 2012), pushing the sensitivity down further. However, in my view one should be careful in over interpreting these results for several reasons:
a) the uncertainties in the assumed radiative forcings are still very large. Recently, Solomon et al. Science (2010, 2011) raised questions about the stratospheric water vapor and aerosol, and just days ago there was another paper arguing for a larger effect of black carbon (http://www.agu.org/news/press/pr_archives/2013/2013-01.shtml, a massive 280 pages…).
b) Results are sensitive to the data used, as shown by Libardoni and Forest DOI: 10.1029/2011GL049431 and others, and particularly sensitive to how the last decade of data is treated. Very different methods (detection attribution optimal fingerprint) have also shown that the last decade makes a difference (Gillett et al. 2011, doi:10.1029/2011GL050226).
c) The uncertainties in the ocean heat uptake may be underestimated by Levitus, and there are additional uncertainties regarding the role of deep ocean heat uptake (Meehl et al. 2011 Nature Climate Change).
Even though we have many of these studies (and I am responsible for a couple of them) I'm getting more and more nervous about them, because they are so sensitive to the climate model, the prior distributions, the forcing, the ocean data, the error model, etc. The reason for this, to a large extent, is that the data constraint is weak, so the outcome (posterior) is dominated by what you put in (prior).
It is important to note that the IPCC assessment of climate sensitivity is based on many lines of evidence (see Fig. 3 in our 2008 review for an overview). The observed energy budget is just one of them. The latest paleoclimate synthesis (Rohling et al. Nature 2012) supports the "likely 2-4.5°C", and all GCMs have sensitivities in the range 2-5°C, the mean in CMIP5 is above 3°C, and once you start evaluating models with observations that tends to get pushed upward (Fasullo and Trenberth, Science 2012).
Finally, note that the effect of the last few years of data is smaller on the transient climate response than on climate sensitivity. It's the transient climate response (TCR) that determines the 21st century warming and peak warming.
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