My reviews to IPCC AR5 WGII

Yesterday the final draft of the IPCC report:

Climate Change 2014: Impacts, Adaptation, and Vulnerability, Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change

has been made public. I have been a reviewer of it. I provided two reviews on its Chapter 2. I feel I can now make public my reviews. Till now I respected the confidentiality terms of IPCC, as I explained in my first review, but I also explained there that I would make my reviews public in due time.

My review on the first draft was made in August 2012 and that on the second draft in May 2013. However, while I publicize my own reviews today, the entire list of the review comments, from all reviewers, to the second draft have been leaked several months ago.

The second draft had substantial changes in comparison to the first one, and several of my review comments were addressed. Thus, in my second review I expressed my general satisfaction and my understanding that addressing my comments was not perfect, given that their views are different from mine. I appreciated the fact that IPCC WGII quoted, albeit too briefly, the criticism to their climate models by some researchers, including some works by my colleagues and me as shown in the following excerpt from the final report (section 3.6.2, Dealing with Uncertainty in Future Climate Change, p. 24):

Some go further, arguing that climate models are not sufficiently robust or reliable to provide the basis for adaptation (Anagnostopoulos et al., 2010; Blöschl and Montanari, 2010; Koutsoyiannis et al., 2008; Wilby, 2010), because they are frequently biased and do not reproduce the temporal characteristics (specifically the persistence or “memory”) often found in hydrological records. It has been argued (Lins and Cohn, 2011; Stakhiv, 2011) that existing water-resources planning methods are sufficiently robust to address the effects of climate change. This view of climate model performance has been challenged and is the subject of some debate (Huard, 2011; Koutsoyiannis et al., 2009; 2011); the critique also assumes that adaptation assessment procedures would only use climate scenarios derived directly from climate model simulations.

Indeed, we go much further than IPCC (and, in particular, than what IPCC says about our works in the above paragraph).

I did not check carefully the final draft against the second one, but I can see that my comments in the second review were not addressed except that there was an additional citation to one of the works I coauthored.

In particular, I was disappointed that my following comment was not addressed:

I reiterate my earlier comment on Hurst. I strongly insist that mentioning the Hurst-Kolmogorov phenomenon (long-term persistence) in the Freshwater Chapter is absolutely necessary and relevant. If hydrologists fail to refer to it, how can we expect from climatologists and scientists from other disciplines to mention it in other chapters? I suggest to refer to it by adding the following paragraph:

“It should be mentioned that many of the trend analyses in the literature are based on classical statistical tests that are based on the assumption of time independence for the tested process. However, the pioneering work by Hurst (1951) [Long term storage capacities of reservoirs, Trans. Am. Soc. Civil Engrs., 116, 776-808, 1951] has shown that hydrological and other geophysical processes are not independent in time but, on the contrary, are characterized by long-range dependence, also known as long-term persistence. The Hurst behaviour is a prominent characteristic of climate (Markonis and Koutsoyiannis, 2013; Koutsoyiannis, 2013). If this behaviour is accounted for, many of the trends rendered as significant by classical statistical tests become insignificant (Cohn and Lins, 2005 [Nature’s style: Naturally trendy, Geophysical Research Letters, 32 (23), doi:10.1029/2005GL024476]).”

However, I took some consolation as, in fact, the climate scientists of Workgroup I, contrary to my guess above, made an implicit mention in Chapter 2 (released several months ago), where they say:

No attempt has been undertaken to further describe and interpret the observed changes in terms of multi-decadal oscillatory (or low-frequency) variations, (long-term) persistence and/or secular trends (e.g., as in Cohn and Lins, 2005; Koutsoyiannis and Montanari, 2007; Zorita et al., 2008; Lennartz and Bunde, 2009; Mills, 2010; Mann, 2011; Wu et al., 2011; Zhou and Tung, 2012; Tung and Zhou, 2013).

This looks an indirect recognition of the superiority of the Hurst-Kolmogorov stochastic dynamics for climate. To admit that “No attempt has been undertaken…” is certainly a first step to the right direction.