One way to judge the reliability of a source, is to see what it states about a topic you are knowledgeable about. I work on homogenization of station climate data and was thus interested in the question how well the IPCC report presents the scientific state-of-the-art on the uncertainties in trend estimates due to historical changes in climate monitoring practices.
Furthermore, I have asked some colleague climate science bloggers to review the IPCC report on their areas of expertise. You find these reviews of the IPCC review report at the end of the post as they come in. I have found most of these colleagues via the beautiful list with climate science bloggers of Doug McNeall.
Large-Scale Records and their UncertaintiesThe IPCC report is nicely structured. The part that deals with the quality of the land surface temperature observations is in Chapter 2 Observations: Atmosphere and Surface, Section 2.4 Changes in Temperature, Subsection 2.4.1 Land-Surface Air Temperature, Subsubsection 188.8.131.52 Large-Scale Records and their Uncertainties.
The relevant paragraph reads (my paragraph breaks for easier reading):
Particular controversy since AR4 [the last fourth IPCC report, vv] has surrounded the LSAT [land surface air temperature, vv] record over the United States, focussed upon siting quality of stations in the US Historical Climatology Network (USHCN) and implications for long-term trends. Most sites exhibit poor current siting as assessed against official WMO [World Meteorological Organisation, vv] siting guidance, and may be expected to suffer potentially large siting-induced absolute biases (Fall et al., 2011).
However, overall biases for the network since the 1980s are likely dominated by instrument type (since replacement of Stevenson screens with maximum minimum temperature systems (MMTS) in the 1980s at the majority of sites), rather than siting biases (Menne et al., 2010; Williams et al., 2012).
A new automated homogeneity assessment approach (also used in GHCNv3, Menne and Williams, 2009) was developed that has been shown to perform as well or better than other contemporary approaches (Venema et al., 2012). This homogenization procedure likely removes much of the bias related to the network-wide changes in the 1980s (Menne et al., 2010; Fall et al., 2011; Williams et al., 2012).
Williams et al. (2012) produced an ensemble of dataset realisations using perturbed settings of this procedure and concluded through assessment against plausible test cases that there existed a propensity to under-estimate adjustments. This propensity is critically dependent upon the (unknown) nature of the inhomogeneities in the raw data records.
Their homogenization increases both minimum temperature and maximum temperature centennial-timescale United States average LSAT trends. Since 1979 these adjusted data agree with a range of reanalysis products whereas the raw records do not (Fall et al., 2010; Vose et al., 2012a).
I would argue that this is a fair summary of the state of the scientific literature. That naturally does not mean that all statements are true, just that it fits to the current scientific understanding of the quality of the temperature observations over land. People claiming that there are large trend biases in the temperature observations, will need to explain what is wrong with Venema et al. (an article of mine from 2012) and especially Williams et al. (2012). Williams et al. (2012) provides strong evidence that if there is a bias in the raw observational data, homogenization can improve the trend estimate, but it will normally not remove the bias fully.
Personally, I would be very surprised if someone would find substantial trend biases in the homogenized US American temperature observations. Due to the high station density, this dataset can be investigated and homogenized very well.
Global mean temperatureWhat the report unfortunately does not discus are the uncertainties in the global temperature record. A good reference for this is still Parker (1994). If there is a next IPCC report, it can hopefully report on the results of the global Benchmarking of homogenization algorithms performed in the International Surface Temperature Initiative.
This IPCC report could have mentioned that NOAA now uses a much better homogenization method as they did before and found biases in the global mean temperature. In the GHCNv3 dataset, the trend in the global mean temperature in the raw data is 0.6°C per century and in the adjusted data it is 0.8°C per century (Lawrimore et al., 2012). The main reason for these biases is probably that past temperatures were too high due to larger radiation errors, especially in the time before Stevenson screens were used.
ConclusionConclusion, there is still a lot we can do to improve our understanding of uncertainties due to non-climatic changes in trend estimates. It would be desirable if a next IPCC would be able to produce stronger statements about global uncertainties in the mean temperature trend (and also for changes in extreme weather). The current report is, however, a honest representation of the scientific literature. And that is what the IPCC is supposed to do.
More reviewsIf you see further reviews of the IPCC report by experts, please let me know in the comments. If you are able to write such a review, but do not have a blog, please consider to comment below or write a guests post.
- Impressions of AR5 from an aerosol forcing point of view by Karsten in the comments below.
- Karsten discuses the direct and indirect effects of aerosols on the radiative forcing. Indirect effects are the effects aerosols have by changing the clouds. "Bottomline: AR5 is a fair representation of the current literature and if at all, there is a tendency to err on the side of lesser drama this time (i.e. lower aerosol forcing)."
- Sea level in the 5th IPCC report by Stefan Rahmstorf at RealClimate.
- Stefan Rahmstorf acknowledges the improvements in the estimates of sea level rise, but still finds the IPCC estimates to be too conservative, too low. A more accessible report on the same issue can be found at IRIN News.
- The IPCC AR5 attribution statement by Gavin Schmidt at RealClimate.
- Gavin Schmidt ends his post: "Bottom line? These statements are both comprehensible and traceable back to the literature and the data. While they are conclusive, they are not a dramatic departure from basic conclusions of AR4 and subsequent literature."
- Mayflies mandibles: as seen in the IPCC report by Richard Telford at Musings on Quantitative Palaeoecology.
- As a warming up exercise to his review of the IPCC report Telford comments on a reference in the report to an article that "should never have been submitted, let alone published". He also states that: "The chapter represents the paper correctly, and its inclusion has no impact on any of the chapters conclusions."
- Aslak Grinsted has written two posts: AR5 sea level rise uncertainty communication failure and Optimistic & over-confident ice sheet projections in AR5 at glaciology.net.
- Grinsted is disappointed in how the sea level rise projection uncertainties are presented in the IPCC AR5. The best estimate and especially the worst case scenario estimate of sea level rise are much too low in his opinion. The reason seems to be that the IPCC does not taking the collapse of the Antarctic ice sheet into account because of large uncertainties.
- AR5: cursory review of chapter 4 (cryosphere) mass balance of Antarctica by William M. Connolley at Stoat.
- Connolley used to work at the British Anarctic Survey and comments on the mass balance of Antarctica. As he has left academia, he can not compare the report to the literature, but he can still comment intelligently. Parental advisory. Explicit IPCC critique.
- Near-term global surface temperature projections in IPCC AR5 by Ed Hawkins at Climate Lab Book.
- This post discusses the new chapter and assessment on "near-term" climate change, which is relevant for adaptation decision making. Hawkins gives three reasons for small differences between his and the IPCC assessment.
- What does the 2013 IPCC Summary Say About Water? by Peter Gleick at Significant Figures.
- This posts lists the important points about water in the Summary for Policy makers. Gleick wrote by mail that the IPCC points and his (more limited) reading of the literature are in agreement.
Other reactions on the IPCC report
- Professor Piers Forster and his 18 tweet summary of the IPCC SPM by Mark Brandon at Mallemaroking
- A series of tweets from IPCC drafting author Professor Piers Forster.
- What Does the New IPCC Report Say About Climate Change? by Steve Easterbrook at Serendipity
- Steve Easterbrook summarises the 8 highlights of the report, each illustrated with a figure. Not directly related, but his recent series on the climate as a system is a great tutorial on systems thinking.
- Michael Mann: Climate-Change Deniers Must Stop Distorting the Evidence (Op-Ed) by Michael Mann at live science
- A first reaction on the IPCC report by Michael Mann, but mainly a rant about the weird debate with climate change deniers
- What Leading Scientists Want You to Know About Today's Frightening Climate Report by Richard Schiffman at The Atlantic
- Forget the end of the title and you get a good report with first reactions from a range of scientists
ReferencesLawrimore, J.H., M.J. Menne, B.E. Gleason, C.N. Williams, D.B. Wuertz, R.S. Vose, and J. Rennie, 2011: An overview of the Global Historical Climatology Network monthly mean temperature data set, version 3. J. Geophys. Res., 116, no. D19121, doi: 10.1029/2011JD016187.
Parker, D.E. Effects of changing exposure of thermometers at land stations. Int. J. Climatol., 14, pp. 1–31, doi: 10.1002/joc.3370140102, 1994.
Venema, V., O. Mestre, E. Aguilar, I. Auer, J.A. Guijarro, P. Domonkos, G. Vertacnik, T. Szentimrey, P. Stepanek, P. Zahradnicek, J. Viarre, G. Müller-Westermeier, M. Lakatos, C.N. Williams, M.J. Menne, R. Lindau, D. Rasol, E. Rustemeier, K. Kolokythas, T. Marinova, L. Andresen, F. Acquaotta, S. Fratianni, S. Cheval, M. Klancar, M. Brunetti, Ch. Gruber, M. Prohom Duran, T. Likso, P. Esteban, Th. Brandsma. Benchmarking homogenization algorithms for monthly data. Climate of the Past, 8, pp. 89-115, doi: 10.5194/cp-8-89-2012, 2012.
Williams, C.N. jr., M.J. Menne, and P.W. Thorne, 2012: Benchmarking the performance of pairwise homogenization of surface temperatures in the United States. J. Geophys. Res., 117, art. no. D05116, doi: 10.1029/2011JD016761.