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The AR4 attribution statement

Filed under: — gavin @ 29 January 2012

Back in 2007, the IPCC AR4 SPM stated that:

“Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”

This is a clear statement that I think is very well supported and correctly reflects the opinion of most climate scientists on the subject (and was re-affirmed in two recent papers (Jones and Stott, 2011;, Huber and Knutti, 2011)). It isn’t an isolated conclusion from a single study, but comes from an assessment of the changing patterns of surface and tropospheric warming, stratospheric cooling, ocean heat content changes, land-ocean contrasts, etc. that collectively demonstrate that there are detectable changes occurring which we can attempt to attribute to one or more physical causes.

Yet, in a paper just out in BAMS (Curry and Webster, 2011) this statement is apparently evidence that IPCC is unable to deal with uncertainty. Furthermore, Judith Curry has reiterated on her blog that the term ‘most’ is imprecise and undefined. For instance:

Apart from the undefined meaning of “most” in AR4 (which was subsequently clarified by the IPCC), the range 50.1-95% is rather imprecise in the context of attribution.

However, Curry’s argument is far from convincing, nor is it well formed (why is there a cap at 95%?). Nor was it convincing when I discussed the issue with her in the comments at Collide-a-Scape last year where she made similar points. Since the C&W paper basically repeats that argument (as has also been noticed by Gabi Hegerl et al who have a comment on the paper (Hegerl et al.)), it is perhaps worth addressing these specific issues again.
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References

  1. G.S. Jones, and P.A. Stott, "Sensitivity of the attribution of near surface temperature warming to the choice of observational dataset", Geophysical Research Letters, vol. 38, pp. n/a-n/a, 2011. http://dx.doi.org/10.1029/2011GL049324
  2. M. Huber, and R. Knutti, "Anthropogenic and natural warming inferred from changes in Earth’s energy balance", Nature Geosci, vol. 5, pp. 31-36, 2011. http://dx.doi.org/10.1038/ngeo1327
  3. J.A. Curry, and P.J. Webster, "Climate Science and the Uncertainty Monster", Bulletin of the American Meteorological Society, vol. 92, pp. 1667-1682, 2011. http://dx.doi.org/10.1175/2011BAMS3139.1
  4. G. Hegerl, P. Stott, S. Solomon, and F. Zwiers, "Comment on “Climate Science and the Uncertainty Monster” J. A. Curry and P. J. Webster", Bulletin of the American Meteorological Society, vol. 92, pp. 1683-1685, 2011. http://dx.doi.org/10.1175/BAMS-D-11-00191.1

The IPCC report on extreme climate and weather events

Filed under: — rasmus @ 19 November 2011

The IPCC recently released the policy-maker’s summary (SREX-SPM) on extreme weather and climate events. The background for this report is a larger report that is due to be published in the near future, and one gets a taste of this in the ‘wordle‘ figure below. By the way, the phrase ‘ET’ in this context does not refer ‘extra-terrestrial’, and ‘AL’ is not a person, but these refer to the way of citing many scholars: ‘et al.

Fig. 1. The text analysis according to http://www.wordle.net/

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CMIP5 simulations

Filed under: — gavin @ 11 August 2011

Climate modeling groups all across the world are racing to add their contributions to the CMIP5 archive of coupled model simulations. This coordinated project, proposed, conceived and specified by the climate modeling community itself, will be an important resource for analysts and for the IPCC AR5 report (due in 2013), and beyond.

There have been previous incarnations of the CMIP projects going back to the 1990s, but I think it’s safe to say that it was only with CMIP3 (in 2004/2005) that the project gained a real maturity. The CMIP3 archive was heavily used in the IPCC AR4 report – so much so that people often describe those models and simulations as the ‘IPCC models’. That is a reasonable shorthand, but is not really an accurate description (the models were not chosen by IPCC, designed by IPCC, or run by IPCC) even though I’ve used it on occasion. Part of the success of CMIP3 was the relatively open data access policy which allowed many scientists and hobbyists alike to access the data – many of whom were dealing with GCM output for the first time. Some 600 papers have been written using data from this archive. We discussed some of this success (and some of the problems) back in 2008.

Now that CMIP5 is gearing up for a similar exercise, it is worth looking into what has changed – it terms of both the model specifications, the requested simulations and the data serving to the wider community. Many of these issues are being discussed in a the current CLIVAR newsletter (Exchanges no. 56). (The references below are all to articles in this pdf).

There are three main novelties this time around that I think are noteworthy: the use of more interactive Earth System models, a focus on initiallised decadal predictions, and the inclusion of key paleo-climate simulations as part of the suite of runs.

The term Earth System Model is a little ambiguous with some people reserving that for models that include a carbon cycle, and others (including me) using it more generally to denote models with more interactive components than used in more standard (AR4-style) GCMs (i.e. atmospheric chemistry, aerosols, ice sheets, dynamic vegetation etc.). Regardless of terminology, the 20th Century historical simulations in CMIP5 will use a much more diverse set of model types than did the similar simulations in CMIP3 (where all models were standard coupled GCMs). That both expands the range of possible evaluations of the models, but also increases the complexity of that evaluation.

The ‘decadal prediction’ simulations are mostly being run with standard GCMs (see the article by Doblas-Reyes et al, p8). The different groups are trying multiple methods to initialise their ocean circulations and heat content at specific points in the past and are then seeing if they are able to better predict the actual course of events. This is very different from standard climate modelling where no attempt is made to synchronise modes of internal variability with the real world. The hope is that one can reduce the initial condition uncertainty for predictions in some useful way, though this has yet to be demonstrated. Early attempts to do this have had mixed results, and from what I’ve seen of the preliminary results in the CMIP5 runs, significant problems remain. This is one area to watch carefully though.

Personally, I am far more interested in the inclusion of the paleo component in CMIP5 (see Braconnot et al, p15). Paleo-climate simulations with the same models that are being used for the future projections allow for the possibility that we can have true ‘out-of-sample’ testing of the models over periods with significant climate changes. Much of the previous work in evaluating the IPCC models has been based on modern period skill metrics (the climatology, seasonality, interannual variability, the response to Pinatubo etc.), but while useful, this doesn’t encompass changes of the same magnitude as the changes predicted for the 21st Century. Including tests with simulations of the last glacial maximum, the Mid-Holocene or the Last Millennium greatly expands the range of model evaluation (see Schmidt (2010) for more discussion).

The CLIVAR newsletter has a number of other interesting articles, on CFMIP (p20), the scenarios begin used (RCPs) (p12), the ESG data delivery system (p40), satellite comparisons (p46, and p47) and the carbon-cycle simulations (p27). Indeed, the range of issues covered I think presages the depth and interest that the CMIP5 archive will eventually generate.

There will be a WCRP meeting in October in Denver that will be very focused on the CMIP5 results, and it is likely that much of context for the AR5 report will be reflected there.

The warm beer chart

Filed under: — gavin @ 13 April 2011

Perhaps a way to connect with Joe Sixpack?

Tagline: If we can pay as much attention to the Earth as we do to our beer, we probably wouldn’t need to worry about global warming.

Design by S. Han, loosely based on IPCC (2007), courtesy of the “Artist as Citizen” initiative. (Full size pdf version)

Wahl-to-Wahl coverage

Filed under: — gavin @ 9 March 2011

Eugene Wahl asked us to post a statement related to some incorrect claims circulating in the blogosphere:

The Daily Caller blog yesterday contained an inaccurate story regarding a correspondence that was part of the emails hacked from East Anglia University Climate Research Unit (CRU) in November 2009.

For the record, while I received the email from CRU as forwarded by Dr. Mann, the forwarded message came without any additional comment from Dr. Mann; there was no request from him to delete emails. At the time of the email in May 2008, I was employed by Alfred University, New York. I became a NOAA employee in August 2008.

The emails I deleted while a university employee are the correspondence I had with Dr. Briffa of CRU regarding the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, all of which have been in the public domain since the CRU hack in November 2009. This correspondence has been extensively examined and no misconduct found. As a NOAA employee, I follow agency record retention policies and associated guidance from information technology staff.

Dr. Eugene R. Wahl

March 9, 2011

Further questions can be addressed to Katy.G.Human -at- noaa.gov

Our comments

These claims are simply the latest attempt to try and manufacture scandals and smear scientists, particularly Mike Mann, based on the UEA emails. The story appears likely to have come from Senator Inhofe’s office who presumably had access to the transcripts taken by the NOAA Office of the Inspector General (whose investigation found no evidence of any wrongdoing by NOAA employees). The story was planted with Steve McIntyre, Anthony Watts, and Chris Horner, and then linked to by Inhofe’s office to provide a little plausible denialability – a rather blatant media spin operation.

But the facts of the case do not support the narrative they are pushing at all. While Jones’ original email was certainly ill-advised (as we stated immediately it came to light in Nov. 2009). Eugene Wahl was not subject to FOIA at the time (since he was not a federal employee) and was not subject to UK FOI anyway since he was working for a US-based university. Nor was he aware of any ongoing FOI actions in any case. In the original emails released, Mann stated that he would notify Wahl of Jones’ email, and his only involvement was to forward the Jones email to Wahl which Wahl’s account confirms.

So what is the actual issue at the heart of this? A single line in the IPCC AR4 report (p466) which correctly stated that “Wahl and Ammann (2006) also show that the impact [of the McIntyre and McKitirck critique] on the amplitude of the final reconstruction [by MBH98] was small (~0.05C)”. This was (and remains) true. During the drafting Keith Briffa corresponded with Eugene Wahl and others to ensure that the final text was accurate (which it was). Claims from McIntyre that this was not allowed under IPCC rules are just bogus – IPCC authors can consult with anyone they like at any time. However, this single line, whose inclusion made no effective difference to the IPCC presentation, nonetheless has driven continuing harassment of everyone involved for no good purpose whatsoever. Wahl and Ammann did show that MM05 made no substantial difference to the MBH reconstruction, whether it got said in the IPCC report or not.

That this inconvenient fact has driven hundreds of blog posts, dozens of fevered accusations, a basket load of FOI requests, and stoked multiple fires of manufactured outrage is far more a testimony to personal obsession, rather than to its intrinsic importance. The science of paleo-reconstructions has moved well beyond this issue, as has the interest of the general public in such minutiae. We can however expect the usual suspects to continue banging this drum, long after everyone else has gone home.


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