Benchmark forecasts for climate change

Green, Kesten C and Armstrong, J. Scott and Soon, Willie (2008): Benchmark forecasts for climate change.

Abstract

Climate is complex, uncertain, and, over horizons that are relevant for policy decisions, varies little. Using evidence-based (scientific) forecasting principles, we determined that for such a situation a naïve “no change” extrapolation method was the appropriate benchmark. We tested this benchmark against global mean temperatures. To be useful to policy makers, a proposed forecasting method would have to provide forecasts that were substantially more accurate than the benchmark. We calculated benchmark forecasts against the UK Met Office Hadley Centre’s annual average thermometer data from 1850 through 2007. The accuracy of forecasts from our naïve model is such that even perfect forecasts would be unlikely to help policy makers. For example, mean absolute errors for 20- and 50-year horizons were 0.18°C and 0.24°C. We nevertheless evaluated the Intergovernmental Panel on Climate Change’s 1992 projected warming rate of 0.03°C-per-year. The small sample of errors from ex ante forecasts for 1992 through 2008 was practically indistinguishable from the naïve benchmark errors. To get a larger sample and evidence on longer horizons we backcast successively from 1974 to 1850. Averaged over all horizons, IPCC errors were more than seven-times greater than errors from the benchmark. Relative errors were larger for longer backcast horizons.

• Item Type: MPRA Paper
• Language: English
• Keywords: backcasting; climate model; decision making; ex ante forecasts; out-of-sample errors; predictability; public policy; relative absolute errors; unconditional forecasts
• Subjects: C - Mathematical and Quantitative Methods > C5 - Econometric Modeling > C53 - Forecasting and Prediction Methods ; Simulation Methods; O - Economic Development, Innovation, Technological Change, and Growth > O2 - Development Planning and Policy; Q - Agricultural and Natural Resource Economics ; Environmental and Ecological Economics > Q5 - Environmental Economics > Q54 - Climate ; Natural Disasters and Their Management ; Global Warming

References

Armstrong, J. S. (1985). Long-Range Forecasting. New York: John Wiley.

Armstrong, J. S. (2001). Principles of Forecasting. Boston: Kluwer.

Armstrong, J. S., & Collopy, F. (1992). Error measures for generalizing about forecasting methods: Empirical comparisons. International Journal of Forecasting, 8, 69-80.

Armstrong, J. S., Green, K. C., & Soon, W., (2008), Polar Bear Population Forecasts: A Public-Policy Forecasting Audit, Interfaces (with commentary and reply), 38, 381-405.

Bergquist, L. (2008). Humans started causing global warming 5,000 years ago, UW study says. Journal Sentinel, posted 17 December, http://www.jsonline.com/news/education/36279759.html

Camp, C. D., & Tung, K.-K. (2007). Surface warming by the solar cycle as revealed by the composite mean difference projection. Geophysical Research Letters, 34, L14703, doi:10.1029/2007GL030207.

Carter, R. M., de Freitas, C. R., Goklany, I. M., Holland, D., & Lindzen, R. S. (2006). The Stern Review: A Dual Critique, Part I: The Science. World Economics, 7, 167-198.

Green, K.C., & Armstrong, J.S. (2007). Global warming: Forecasts by scientists versus scientific forecasts, Energy & Environment, 18, 997-1022.

Hansen, J. (2008). Tipping point: Perspective of a climatologist. In State of the Wild 2008-2009: A Global Portrait of Wildlife, Wildlands, and Oceans. W. Woods, Ed. Wildlife Conservation Society/Island Press, pp. 6-15.

IPCC (1990). Climate Change: The IPCC Scientific Assessment. Edited by J.T. Houghton, G.J. Jenkins, and J.J. Ephraums. Cambridge University Press: Cambridge, United Kingdom.

IPCC (1992). Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment. Edited by J.T. Houghton, B.A. Callander, and S.K. S.K. Varney. Cambridge University Press: Cambridge, United Kingdom.

IPCC (2007). Summary for Policymakers, in Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Koutsoyiannis, D., Efstratiadis, A., Mamassis, N., and Christofides, A. (2008). On the credibility of climate predictions. Hydrological Sciences Journal, 53, 671–684.

Lindzen, R. S. (2009). Climate Science: Is it currently designed to answer questions? Forthcoming in proceedings of Creativity and Creative Inspiration in Mathematics, Science, and Engineering: Developing a Vision for the Future: San Marino, August 2008.

McKibben, W. (2007). Warning on warming. New York Review of Books, 54, 15 March.

McKitrick, R., & Michaels, P. J. (2007). Quantifying the influence of anthropogenic surface processes and inhomogeneities on gridded global climate data. Journal of Geophysical Research, 112, doi:10.1029/2007JD008465.

Soon, W. (2007) Implications of the secondary role of carbon dioxide and methane forcing in the climate change: Past, present and future. Physical Geography, 28, 97-125.

Soon, W. (2009). The solar Arctic connection on multidecadal to centennial timescales: Empirical evidence, mechanistic explanation, and testable consequences. Physical Geography, under review.

Theil, H. (1966). Applied Economic Forecasting. Chicago: Rand McNally.

Tierney, J. (1990). Betting the planet. New York Times, December 2.