Global Warming: Experts’ Opinions versus Scientific Forecasts

Studies | Global Warming

No. 308
Friday, February 01, 2008
by Kesten C. Green and J. Scott Armstrong


Notes

  • This paper is based substantially on Kesten C. Green and J. Scott Armstrong, “Global Warming: Forecasts by Scientists versus Scientific Forecasts,” Energy and Environment, Vol. 18, Nos. 7 & 8, 2007, pages 997-1,021.
  • Intergovernmental Panel on Climate Change, “About IPCC,” undated.  Available at http://www.ipcc.ch/about/index.htm.  Access verified December 10, 2007.
  • Intergovernmental Panel on Climate Change, Climate Change 2007: The Physical Science Basis (New York: Cambridge University Press, 2007).  Available at http://ipcc-wg1.ucar.edu/wg1/wg1-report.html.  Access verified December 10, 2007.
  • Many observers have claimed the IPCC presents scenarios or projections rather than forecasts.  See K. E. Trenberth, “Predictions of Climate,” Climate Feedback: The Climate Change Blog, Nature.com, June 4, 2007.  Available at http://blogs.nature.com/climatefeedback/2007/06/predictions_of_climate.html.  Access verified December 10, 2007.  A forecast or prediction is an estimate of actual values in a future time period (for time series) or for another situation (for cross-sectional data).  The terms “scenario” and “projection” appear to be used in the IPCC’s Fourth Assessment Report to indicate that it provides “conditional forecasts.”  As it happens, in Chapter 8, “Climate models and their evaluation,” the report uses the word “forecast” and its derivatives 37 times, and “predict” and its derivatives 90 times.  Furthermore, the majority (31 of the 51) of scientists who responded to a survey for this study agreed that the IPCC report is the most credible source of forecasts (not “scenarios” or “projections”) of global average temperature.
  • W. Ascher, Forecasting: An Appraisal for Policy Makers and Planners (Baltimore, Md.: Johns Hopkins University Press, 1978).
  • P.E. Tetlock, Expert Political Judgment: How Good Is It? How Can We Know? (Princeton, N.J.: Princeton University Press, 2005).
  • J. Scott Armstrong, “Extrapolation for time-series and cross-sectional data,” in J. S. Armstrong, ed., Principles of Forecasting (Norwell, Mass.: Kluwer Academic Press, 2001).
  • Reid Bryson, the most-cited climatologist in academic studies worldwide, said a model is “nothing more than a formal statement of how the modeler believes that the part of the world of his concern actually works.” Reid A. Bryson, “Environment, Environmentalists, and Global Change: A Skeptic’s Evaluation,” New Literary History, Vol. 24, No. 4, 1993, pages 783-795.
  • Joseph Bast and James M. Taylor, Scientific Consensus on Global Warming (Chicago, Ill.: Heartland Institute, 2007).  Available at http://downloads.heartland.org/20861.pdf.  Access verified December 10, 2007.  (It includes the responses to all questions in the 1996 and 2003 surveys by Dennis Bray and Hans von Storch as an appendix.)
  • Polls show that the general public is also skeptical of the ability of climate models to accurately portray the future: 40 percent agreed that “climate change was too complex and uncertain for scientists to make useful forecasts,” while 38 percent disagreed.  Paul Eccleston, “Public ‘in denial’ about climate change,” Telegraph.co.uk, March 7, 2007.  Available at http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/07/03/eawarm103.xml.  Access verified December 10, 2007.
  • Orrin H. Pilkey and Linda Pilkey-Jarvis, Useless Arithmetic: Why Environmental Scientists Can’t Predict the Future (New York, N.Y.: Columbia University Press, 2007).
  • Bryson, “Environment, Environmentalists, and Global Change.”
  • Numerous studies have concluded that the use of climate models for forecasting has failed.  See, for example, Robert C. Balling, “Observational surface temperature records versus model predictions,” in P. J. Michaels, ed., Shattered Consensus: The True State of Global Warming (Lanham, Md.: Rowman & Littlefield, 2005), pages 50-71; John Christy, “Temperature Changes in the Bulk Atmosphere: Beyond the IPCC,” in Michaels, Shattered Consensus, pages 72-105; Oliver W. Frauenfeld, “Predictive Skill of the El Nino-Southern Oscillation and Related Atmospheric Teleconnections,” in Michaels, Shattered Consensus, pages 149-182; Eric S. Posmentier and Willie Soon, “Limitations of Computer Predictions of the Effects of Carbon Dioxide on Global Temperature,” in Michaels, Shattered Consensus, pages 241-281.
  • Freeman J. Dyson, “Heretical Thoughts About Science and Society,” Edge: The Third Culture, August 8, 2007.  Available at http://www.edge.org/3rd_culture/dysonf07/dysonf07_index.html. Access verified December 10, 2007.
  • R. M. Carter, “The myth of dangerous human-caused climate change,” The Australasian Institute of Mining and Metallurgy New Leaders Conference, Brisbane, Queensland, May 3, 2007, pages 61-74.  Available at http://members.iinet.net.au/~glrmc/new_page_1.htm. Access verified December 10, 2007.
  • C. Essex and R. McKitrick, Taken by Storm: The Troubled Science, Policy & Politics of Global Warming (Toronto, Ca.: Key Porter Books, 2002).
  • D.A. Stainforth et al., “Uncertainty in predictions of the climate response to rising levels of greenhouse gases,” Nature, Vol. 433, 2005, pages 403-406.
  • David Bellamy and Jack Barrett, “Climate stability: an inconvenient proof,” Proceedings of the Institution of Civil Engineers – Civil Engineering, Vol.160, May 2007, pages 66-72.
  • Ibid., page 72.
  • Noted by former Colorado State Climatologist Roger Pielke Sr.  See “Interview By Marcel Crok Of Roger A. Pielke Sr.,” April 30, 2007.  Available at http://tinyurl.com/2wpk29.  Access verified December 10, 2007.
  • Trenberth, “Predictions of climate.”
  • M. Taylor, “An evaluation of NIWA’s climate predictions for May 2002 to April 2007,” Climate Science Coalition, 2007.  Available at http://nzclimatescience.net/images/PDFs/climateupdateevaluationtext.pdf. Data available at http://nzclimatescience.net/images/PDFs/climateupdateevaluationcalc.xls.pdf.
  • New Zealand Climate Science Coalition, “World climate predictors right only half the time,” Scoop Independent News (New Zealand), media release, June 7, 2007.  Available at http://www.scoop.co.nz/stories/SC0706/S00026.htm.  Access verified December 10, 2007.
  • This study is the only comprehensive review of climate forecasting efforts to date, though there have been more limited reviews of some aspects of the IPCC’s forecasting principles and assessments of the actual accuracy of the forecasts made.  For example, the National Defense University (NDU) forecasting process (described above) was criticized in an audit by T. R. Stewart and M. H. Glantz for lacking awareness of proper forecasting methods.  The audit was hampered because the organizers of the NDU study said that the raw data had been destroyed.  Judging from a Google Scholar search for citations, climate forecasters have paid little attention to that paper.  T. R. Stewart and M. H. Glantz, “Expert judgment and climate forecasting: A methodological critique of ‘Climate Change to the Year 2000,’” Climate Change, Vol. 7, 1985, pages 159-183.
  • Bryson, “Environment, Environmentalists, and Global Change,” pages 783-795.
  • The best selling textbook on forecasting methods was referenced twice in a search for the term “global warming,” but neither citation related to the prediction of global mean temperatures.  S. Makridakis, S. C. Wheelwright and R. J. Hyndman, Forecasting: Methods and Applications, 3rd ed. (Hoboken, N.J.: John Wiley, 1998).
  • As discussed in the sidebar, the majority of scientists responding to our inquiries concerning what climate forecasts were most credible and how they were determined referenced Chapters 8 through 10 of the IPCC WG1 2007 report, Climate Change 2007.  Available at http://ipcc-wg1.ucar.edu/wg1/wg1-report.html. Access verified December 10, 2007.
  • Including Chapter 10 of the IPCC Report, Gerald A. Meehl et al., “Global Climate Projections,” in Climate Change 2007, pages 747-846. Available at http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch10.pdf. Access verified December 10, 2007.
  • David R. Henderson, “Governments and Climate Change Issues: The Case for Rethinking,” World Economics, Vol. 8, No.2, 2007, pages 183-228.  Available at http://forecastingprinciples.com/Public_Policy/Henderson2007paper.pdf.  Access verified December 10, 2007.
  • Freeman Dyson wrote that “The real world is muddy and messy and full of things that we do not yet understand.” Dyson, “Heretical Thoughts About Science and Society.”
  • Accurate direct measurements of tropospheric global average temperature have only been available since 1979, and they show no evidence for greenhouse warming.  Surface thermometer data, though flawed, show temperature stasis since 1998.  Carter, “The myth of dangerous human-caused climate change.”
  • H. Le Treut et al., “Historical Overview of Climate Change,” in IPCC, Climate Change 2007.  Available at http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch01.pdf.  Access verified December 10, 2007.  See also, Willie Soon, “Implications of the secondary role of carbon dioxide and methane forcing in climate change: Past, present and future,” Physical Geography, July 4, 2007.  Available at http://arxiv.org/ftp/arxiv/papers/0707/0707.1276.pdf.  Access verified December 10, 2007.
  • Carter, “The myth of dangerous human-caused climate change.”
  • Even with perfect knowledge of emissions, uncertainties in the representation of atmospheric and oceanic processes by climate models limit the accuracy of any estimate of the climate response.  Natural variability, generated both internally and from external forcings such as changes in solar output and explosive volcanic eruptions, also contributes to the uncertainty in climate forecasts. P. A. Stott and J. A. Kettleborough, “Origins and estimates of uncertainty in predictions of twenty-first century temperature rise,” Nature, Vol. 416, 2002, pages 723-726.
  • For example, the phrases “It is not yet possible to determine which estimates of the climate change cloud feedbacks are the most reliable,” and “Despite advances since the TAR (Third Assessment Report), substantial uncertainty remains in the magnitude of cryospheric feedbacks within AOGCMs.”  (Cryospheric feedbacks are responses of frozen areas of the earth — the world’s Arctic and Antarctic regions, and glaciers — to climate changes.  AOGCMs are general circulation models of the ocean/atmosphere make-up and interaction.)  The following words and phrases appear at least once in the Chapter: unknown, uncertain, unclear, not clear, disagreement, not fully understood, appears, not well observed, variability, variety, unresolved, not resolved, and poorly understood.  David A. Randall et al., “Climate Models and their Evaluation,” in IPCC, Climate Change 2007, page 593.  Available at http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch08.pdf.  Access verified December 10, 2007.
  • Ibid., pages 608-609.
  • P. G. Allen and R. Fildes, “Econometric Forecasting,” in Armstrong, Principles of Forecasting; J. Scott Armstrong, Long-Range Forecasting: From Crystal Ball to Computer (New York, N.Y.: Wiley-Interscience, 1985); G. T. Duncan, W. L. Gorr and J. Szczypula, “Forecasting Analogous Time Series,” in Armstrong, Principles of Forecasting; D. Wittink and T. Bergestuen, “Forecasting with Conjoint Analysis,” in Armstrong, Principles of Forecasting.
  • H. Halide and P. Ridd, “Complicated ENSO models do not significantly outperform very simple ENSO models,” International Journal of Climatology, 2007, in press.
  • G. C. Hegerl et al., “Understanding and Attributing Climate Change,” in IPCC, Climate Change 2007.  Available at http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch09.pdf. Access verified December 10, 2007.
  • Armstrong, Principles of Forecasting.
  • As noted, the ratings in a forecasting audit involve some judgment.  As a check on the auditors’ judgments, the detailed ratings were sent to 240 of the scientists and policymakers surveyed earlier for information on the use of forecasting principles. They were asked to review the paper and to identify any inaccuracies. They were also invited to make their own ratings for publication at publicpolicyforecasting.com.  As of this writing, none have done so.
  • The authors’ ratings of the processes used to generate the forecasts presented in the IPCC report are provided on the Public Policy Forecasting Special Interest Group Page at forecastingprinciples.com.  These ratings were posted in late June 2007, when the authors’ paper was presented at the International Symposium on Forecasting in New York.
  • David A. Randall et al., “Climate Models and their Evaluation.”
  • Because reliability is an issue with rating tasks, the authors sent out a general request for experts and several colleagues to use the Forecasting Audit Software to conduct their own audits.  At this writing, none have done so.
  • The final ratings are fully disclosed in the Special Interest Group section of the forecastingprinciples.com site that is devoted to Public Policy (publicpolicyforecasting.com) under Global Warming.

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