BACKGROUND
In 2007 Scott Armstrong, Professor of Marketing at the Wharton School of the University of Pennsylvania and author of the book Principles of Forecasting: A Handbook for Researchers and Practitioners, issued the so-called “global warming challenge” to Al Gore, involving a $10,000 bet, with the winnings to be donated to charity.[1][2] Gore declined to accept the challenge, but in 2018 Professor Armstrong is claiming that Gore would have lost, had he accepted the challenge.[1][3]
DETAILS OF THE BET
The proposed bet was that Professor Armstrong’s “naive” model of no warming would outperform the Intergovernmental Panel on Climate Change’s model of 3 °C of warming per century, over the decade from the beginning of 2008 to the end of 2017. The winning model was to be the one that produced the lesser cumulative absolute error, using the actual measured temperature record as a reference.[2] (For the mathematicians among the readers, the cumulative absolute error E is calculated using the formula E = Σ|et|where e is the error at time t.)
WHY GORE WAS WISE TO DECLINE THE CHALLENGE
Professor Armstrong styled his wager “the global warming challenge,” but in fact this is a misnomer. Global warming is driving modern climate change, the key word being climate. For as the International Meteorological Organization (predecessor of today’s World Meteorological Organization) determined about a century ago, a period of thirty years is required to talk about climate; anything less than that is just weather.[4] Thus if Gore had accepted the challenge, win or lose the result would have been meaningless (in the sense of not being statistically significant), but if he had lost, it would have provided another talking point to the organized campaign of climate-change denial.[5]
A QUICK WAY TO SEE THAT GORE WOULD HAVE WON THE CHALLENGE
Professor Armstrong is using the satellite temperature dataset kept by the University of Alabama in Huntsville as the arbiter (i.e., reference) in his claim that he would have won the challenge.[3][6] A convenient way of accessing the UAH satellite data with an accompanying trend line is provided by the Wood for Trees website.[7] The trend line has a slope of 0.4 °C per decade, compared with a slope of 0.3 °C per decade for the IPCC’s model. Thus the satellite data actually shows more warming than the IPCC’s model. It is worth noting that the goodness-of-fit of the trend line has a R2 value of only 0.3, indicating a poor fit (a perfect fit would have a value of unity), confirming that over a decade we are seeing mostly just weather and not climate.
THEN WHY IS PROFESSOR ARMSTRONG CLAIMING THAT HE WOULD HAVE WON THE CHALLENGE?
The Professor’s claim is based—in this writer’s considered opinion--on an error in the way he sets up the IPCC model. He makes the IPCC model intersect his naive model—a flat line corresponding to the average temperature anomaly (see Reference 8) from 2008 through 2017—at the beginning of the decade, as shown in the Professor’s chart in Reference 9 below and the second chart above. This is incorrect, and is equivalent to adding an offset error to the IPCC’s model. The total error is a combination of the random and offset errors. It is the contribution from the improperly introduced offset error that makes it appear as if the IPCC’s model produces a greater cumulative error than the naive model. The correct way of setting up the IPCC’s model is to make it intersect the naive model at the center of the decade (this is equivalent to taking as given the IPCC’s slope and regressing only the intercept, ensuring that the regressed model and the data have the same mean). When the offset error is eliminated by correctly setting up the IPCC’s model, it has a lower cumulative absolute error than the naive model over the entire decade. All of this is clearly seen in the chart at the top of the page.
REFERENCES
- Maxim Lott, Al Gore would have lost global warming bet, academic says, Fox News, 26 January 2018, www.foxnews.com/...
- The Global Warming Challenge, www.theclimatebet.com/…
- Tipping point 10 years on: Who won the Armstrong-Gore “bet” on the climate?, www.theclimatebet.com
- FAQ: What is Climate?, World Meteorological Organization, www.wmo.int/…
- Duncan Geere, Billion-dollar climate denial network exposed, Wired, 21 December 2013, www.wired.co.uk/…
- UAH satellite temperature dataset, Wikipedia, en.wikipedia.org/…
- Wood for Trees, www.woodfortrees.org , woodfortrees.org/…
- Global Temperature Anomalies, National Oceanic and Atmospheric Administration, www.climate.gov/…
- Temperature deviation from average in degrees C, http://www[dot]theclimatebet.com/graph-full.png (Note: This image is not whitelisted by Daily Kos.)