Preface: This update now covers two bets: my 2014 bet with fellow economists Bryan Caplan and Alex Tabarrok (I bet that global temperatures would continue to rise through 2029, they bet for flatlining temperatures) and 2024 bet with Zeke Hausfather and Nick van Osdol about fossil fuel consumption (I bet that consumption of coal, oil, natural gas, and total fossil fuels would continue to rise past 2029, they bet for peaks).

Bet #1 with Bryan Caplan and Alex Tabarrok

Back in 2014 I made a global warming bet with fellow economists Bryan Caplan and Alex Tabarrok about global temperatures over the following 15 years (2015-2029) compared with the previous 15 years (2000-2014). The bet can be illustrated with this graphic, so I’m calling it our “traffic light” bet:

The short version is that the red line at 1.01°C shows how warm global average temperatures have been, relative to the 20th century average, during 2015-2025, the first 11 years of our 15-year betting period. The yellow line at 0.68°C shows the finish line for the bet: if the red line is above the yellow line after another 4 years then I win the bet, and otherwise they win the bet. And the green line at -0.25°C shows how warm global  average temperatures can be over the next 4 years for Bryan and Alex to win the bet. The good news for Bryan and Alex is that they can still win our global warming bet if average temperatures for the next 4 years are about 1.24°C (=1.01-[-0.25]) lower than the average for the past 11 years! The bad news is that, compared to last year, the red line moved up, from 1.00 to 1.01, because last year was quite warm. The really  bad news: the green line moved way down, from 0.05 to -0.25, partly because of last year’s warmth but mostly because another year has gone by.

The long version (mostly copied from 2025, see also 2024, 2023, 2022, 2021, 2020, 2019, 2018) starts with a 2014 tweet from Bryan to me:

Bryan and I ended up making a bet about whether the NOAA global land-ocean average for 2015-2029 (for which the years-to-date are represented by the red line) would be more or less than the average for 2000-2014 plus 0.05°C (the yellow line). Bryan asked me for 2 to 1 odds, but I was so confident I gave him 3 to 1 odds. (Keep in mind that IPCC 2007 projected warming of 0.2C per decade for the next two decades, and IPCC 2013 said something similar.) I was also confident enough to suggest an “exploding bet”—where the amount doubles every year unless someone gives in—but he declined. So Bryan and I bet his $333.33 against my $1000, and then for good measure I gave his colleague Alex Tabarrok 5 to 1 odds, his $200 against my $1000, on the same topic:

So far it’s not looking so good for the Bryan and Alex side of the bet. I’ll post another update in a year or three; for now let me confess that I’m not so good at econometrics—I’ll leave that to folks like Steve Levitt, who noted in his 2009 book Superfreakonomics that “a little-discussed fact [is that] over the past several years, the average global temperature… has in fact decreased“—but I will humbly suggest that you take a good look at the following image, which shows the raw data from the “traffic light” graph, before you write me to ask if you can throw your money on the table as well:

This graphic also suggests that Bryan may not have been quite right in 2018 when he said, “But we’re only a few years into a 15-year bet, so I won’t start fretting until 2025 or so.” In any case, I’m happy to bet more about this with Bryan, Alex, or anybody else with good references and great credit!

Bet #2 with Zeke Hausfather and Nick van Osdol

Bet #2 is with Zeke Hausfather and Nick van Osdol, per the Twitter/X links below. I’m betting that globalcarbonbudget.org will show new peaks for coal, oil, natural gas, and total fossil fuel consumption in 2030 or 2031, they’re betting for peaks in the 2020s. (I’m betting $100 on each of those four items with Zeke and Nick, so I’m betting $800 total.)

Here’s the key graph from the 2025 GCB report. It shows that CO2 from each of coal, oil, and natural gas (and therefore their sum) rose by about 1% from 2024 to 2025. Any or all of them could still peak in the 2020s, but I fear that’s wishful thinking: