A Bet on Global Warming

Made in 2007, at the height of the alarm. Payments in 2020, 2025, and 2030.


It was 2007, at the height of the alarm over global warming. We could see the theory about carbon dioxide had no empirical evidence to back it, only a sensitivity calculation and computer models based on theory. Yet the hype was huge.

Along came Brian Schmidt, a lawyer from San Francisco and fellow graduate of Stanford University, who seemed like a sensible and pleasant warmist. He was offering bets on the temperature outcomes for the next decade or two, challenging skeptics to put their money where their mouths were. A fair point. Brian wanted to bet that the global temperature would rise in line with the IPCC predictions of the time; for us to win, the warming would have to be significantly below that predicted rate.

Back in 2007 there was no talk of a pause or hiatus in the warming. Al Gore's movie was all the rage, and the only question seemed to be how much warming would occur and when. Yet we were pretty sure the IPCC were exaggerating or even seriously wrong, because there had been a steady accumulation of empirical evidence against the theory and a suspicious dearth of observations to prove that the rising carbon dioxide concentration had actually caused most of the warming to date.

This seemed like a pretty good opportunity, even though in 2007 we had no real idea of what was causing the global warming or when it would relent. A bet was made.

(We didn't discover the relationship between solar output and earthly temperatures in the frequency domain until 2013. This relationship, which led to the notch-delay solar theory, is that the Earth's surface temperature follows the Sun's total output but with a delay of one sunspot cycle. The Sun's output turned down significantly from 2004, and the sunspot cycle following that was about 13 years. So the surface temperature might be expected to turn down on average from about 2017. This would mean we placed the bet too early. But we didn't know that in 2007.)

Details of the Bet

The IPCC was predicting warming at a rate of 0.20 °C per decade, and we fixed on 0.15 °C per decade as the crucial rate for the bet. There is a margin for ties. Brian wins if the world warms at more than 0.17 °C per decade; we win it warms at less than 0.13 °C per decade; even odds. We also made bets at 2 to 1 odds, with Brian winning if warming is at least 0.11 °C per decade while we win double if it warms at less than 0.09 °C per decade.

There are bets over 10, 15, and 20 years, for six bets in total. Brian stands to win US$1,000 per bet, so we have US$6,000 at risk and Brian has US$9,000 at risk.

The global temperature is defined for the bet as the centered average of the GISS temperatures over 5 years. The starting point for all the bets is the average temperature over 2005–2009, and the end points of the bets are 2015–2019, 2020–2024, and 2025–2029. So the bets become payable at the beginning of 2020, 2025, and 2030.

Brian posted the details of the bet on his (previous) website, and kindly allowed me to post my reasons for making the bet

How are We Doing?

Many say there has been a pause or hiatus in global warming, starting around 2000 or maybe a few years before, which continues to at least 2015. This is much easier to see in retrospect, because the temperature fluctuates and it is the trends that are at issue here. The pause is of course an excellent development for our side of the bet, and for the planet (as Brian cheerfully acknowledges, “Best case though is that I lose everything.”).

However the fluctuations due to the large La Nina in 2008 and the massive El Nino in 2016 have given Brian a leg up, which is unfortunate because El Ninos and La Ninas seem to have little to do with the underlying trend we are betting on. At this point in late 2018, with a year left to run, it is almost certain that Brian will win the first pair of bets, due to be settled in 2020.

Brian has commented in 2011, 2012, 2013, 2015, 2016, and 2017.

Joanne has commented in 2013 and 2014.
GISTEMP from 2005

Taking a wider perspective to reduce the effect of temporary fluctuations, and using the more credible satellite temperature record (covers almost the whole planet, no thermometers in artificially warming locations, past readings not adjusted), the trend is a little less than our criterion of 0.15 °C per decade and much less than the oldest firm prediction from the IPCC of 0.30 °C per decade:

UAH from 1979