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.

So this seemed like a pretty good opportunity. A bet was made.

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?

It is now widely acknowledged that there is a pause or hiatus in global warming, starting around 2000 or maybe a few years before, which continues as of this writing (Feb. 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 large El Nino in 2015 and 2016 has put Brian ahead, which is unfortunate because El Ninos and La Ninas seem to have little to do with the underlying trend we are betting about. Still, three years left to run.

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

Joanne has commented in 2013 and 2014.
GISTEMP from 2005