Science Story: the Making of a Sea Level Study

With the small number of independent data points we needed to make sure we were not ‘fitting an elephant‘, so I read up on statistics during winter 2008/2009, and in particular, information theoretical methods like the Akaike Information Criterion. The model intercomparison was useful for just that. I’m not the only one studying these ideas, and I learnt a lot from tamino and James Annan’s Empty Blog. Jaynes (2003) was also on my 2009 Christmas reading list; Hypothesis testing, null and alternative hypotheses, confidence bounds and all that, is a traditional approach to statistics that is easily misunderstood and often misused. Statistical refutations of “silly null” hypotheses abound — like the silly null of no relationship between temperature and sea level rise. If this sounds all cryptic to you, I don’t blame you. Pick up Jaynes (2003), it’s an eye-opener.

As part of his contribution, Stefan tightened up the draft paper to be suitable for submission to Nature. Nature gave us some very helpful reviews which we used to further improve our manuscript. The most useful reviewer remark had to do with the extraction of water from underground aquifers, a process potentially almost as important as the artificial reservoir storage that we did take into account — only, nowhere in the literature was there an equally painstaking accounting exercise to be found as what Ben Chao and colleagues did for the reservoirs. So, we settled for a sensitivity analysis, skillfully whipped up by Stefan.

Nature turned us down, like they do over 90% of manuscripts; had they accepted, the paper would have been out already in summer. We resubmitted to PNAS who obtained three further helpful reviews, the paper was improved yet again and finally published in December. As it happens, this landed it right on top of the Copenhagen meeting.

Stefan tells me that we have exchanged over a thousand emails in the run-up to this paper. I see some poetry in that number being close to that of the East Anglia stolen email selection. Easy, informal email plays a vital role in the work of climatologists, and the loss of trust in its confidentiality could be very disruptive for the science: if the internal discussions of an authoring team would have to be expressed with the same care as the finished product, not a lot of authoring would get done.

Would I have dared, or managed successfully, to submit to a top journal all on my own? Hardly. It is an illusion to think that you can just enter a field that’s not your own and become a productive researcher, whatever you might read or what denialists-of-service may pretend. There is a lot of domain knowledge involved, and precious little of it is simple. In this case, I did learn a lot (and I continue to do so), but this takes both a willingness to learn, and great teachers. RealClimate, and the community it represents, are an indispensable resource for that.

Still waiting for Al Gore’s cheque…

P.s. Over at Nature Stefan has a commentary on sea level today.


Martin Vermeer and Stefan Rahmstorf (2009): Global sea level linked to global temperature, Proceedings Nat. Acad. Sci. 2009 vol 106 no. 51 pp. 21527-21532, DOI: 10.1073/pnas.0907765106, open access link

Jonathan Overpeck and Jeremy L. Weiss (2009): Projections of future sea level becoming more dire, Proceedings Nat. Acad. Sci. 2009 vol. 106 no. 51, pp. 21461-21462, DOI: 10.1073/pnas.0912878107 link.

Stefan Rahmstorf (2007): A Semi-Empirical Approach to Projecting Future Sea-Level Rise, Science 315, 368-370, DOI: 10.1126/science.1135456 link

B.F. Chao, Y.H. Wu and Y.S. Li (2008): Impact of Artificial Reservoir Water Impoundment on Global Sea Level, Science, 320, 212-214 link

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