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Don’t climate bet against the house « RealClimate

Decades ago (it seems) when perhaps it was still possible to have good faith disagreements about the attribution of current climate trends, James Annan wrote a post here summarizing the thinking and practice of Climate Betting. That led to spate of wagers on continued global warming (a summary of his bets through 2005 and attempts to set up others is here).

There were earlier bets, the most well known perhaps was the one for $100 between Hugh Ellsaesser and Jim Hansen in 1989 on whether there would be a new temperature record within three years. There was (1990), and Ellsaesser paid up in January 1991 (Kerr, 1991). But these more recent bets were more extensive.

William Connolley (an early contributor to this site) was also a prolific bettor, and often took on the wilder predictions of sea ice collapse successfully. His tally of wins (mostly through anticipation of linear trends in summer sea ice) was in contrast to some rather fanciful extrapolations. One winning bet (against Joe Romm no less, and joint with James and Brian Schmidt) was related to when we would see essentially “ice free” conditions in the Arctic, with William taking the side of ‘not yet’ (note this has yet to be paid out).

But not all bets were made in good faith. James’ 2005 $10,000 bet with Galina Mashnich and Vladimir Bashkirtsev on whether 2012-2017 would be warmer than 1998-2003 resulted in a clear win for James, but the Russian scientists have not paid up, or even responded to email in the subsequent two years.

Decade-by-decade warming is very robust.

With the close of 2020, a number of other climate bets have been resolved – all in favor of the people who bet on more warming. Dana Nuccitelli and Rob Honeycutt had a bet with blogger Pierre Gosselin and his readers that 2011 – 2020 would be warmer than the decade of 2001 – 2010 (and indeed it was). This was a charity bet with multiple people, some of whom (including Gosselin) have paid up, though many have not. Somewhat surprisingly, Gosselin has bet again on the next decade being cooler than the last. There’s a saying somewhere about fools and their money…

Even bets for much lower “steaks” have had trouble getting resolved. Zeke Hausfather has a running bet with Joe Bastardi (ex-Accuweather) on year-to-year warming in the UAH satellite record. By Zeke’s reckoning, Joe owes him the equivalent of five (or maybe four) steak dinners:

There have of course been many bets offered that were not taken up.

For instance, it was quite revealing that Richard Lindzen was agreeable to betting on global cooling, but only with such extreme odds that actually placed him well inside the mainstream.

In another example, Bastardi was offered a much bigger bet by Bill Nye ($10,000) on whether 2016 would be a top ten year, and whether this last decade would be the warmest on record [Narrator: they were]. But perhaps that was a little rich for his taste.

The contributors at RealClimate offered a bet to Noel Keenlyside and colleagues against their prediction of global cooling. This was not taken up either (and yes, they would have won easily).

Another (rather oddly structured) bet was proposed in 2007 by forecasting ‘guru’ Scott Armstrong to Al Gore (who rightly ignored it). Armstrong used to keep up a commentary on how his imaginary bet was going (though it hasn’t been updated since July 2020). This bet was odd not only because Armstrong made up a forecast trend from IPCC of 0.3ºC/dec (the forecasts in AR4 (2007) were much closer to 0.2ºC)/dec, but because the scoring was cumulative on whether each individual monthly anomaly in the UAH TLT record was closer to no-change or to the “IPCC” trend. This is a noisy metric on short time scales resembling a random walk. Nonetheless, to the surprise (I’m sure) of Prof. Armstrong, the trend in UAH TLT is more than 0.3ºC/dec from 2007-2020, though his preferred metric has yet to flip (it’s close to doing so, and the equivalent skill metric for annual values already has).

So what have we learned?

Originally, the idea of betting was to get a sense of how confident predictive claims were. The more confident one was, the smaller odds one would accept. The hope would be to distinguish rhetorical claims from claims that were sincerely held. However, if people are prepared to make casual (no escrow) bets that they have no intention of paying up on if they lose, the ability to distinguish good and bad faith claims vanishes. It turns out some people’s desire to not be publicly shamed by being a known deadbeat is not as strong as one might have anticipated.

But the bigger lesson is actually how predictable aspects of the climate are. Decade by decade increases in temperature are a very robust prediction from the current rise in GHGs. New records will continue to be set in annual global temperatures. While weather can easily shape a season, the longer term trends (so far at least) appear quasi-linear.

The winners in these bets for the most part relied on relatively straightforward projections of forcings and response, without dramatic non-linearities. Past performance is no guarantee of future gains, but at the global level, this seems like a successful formula for winning any new climate bets.

It’ll be probably be harder to find takers in future.


  1. R.A. KERR, “Global Temperature Hits Record Again”, Science, vol. 251, pp. 274-274, 1991.

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