Even if you’ve been living under a rock for the last year, you’ve probably heard of Polymarket, the popular online betting platform that allows people to gamble on virtually any aspect of modern life, from Donald Trump’s next military action to the price of oil or the results of elections. You can even bet on the temperature in a certain place at a given time. But, as is often the case, certain bets can be manipulated.
Météo-France, the French weather forecasting service, believes that a weather station at Charles de Gaulle airport in France was used to manipulate bets placed on Polymarket on what the temperature would be in the French capital on certain days of March and April.
Data shows that on some days, more than $500,000 was placed on bets on the temperature in Paris, with some wallets pocketing around $280,000 by betting that the temperature in Paris would reach 19 °C on April 15. Surprisingly, at approximately 9:30 p.m., the temperature reached 22°C, whereas it had been just 18°C in the middle of the afternoon.
Sébastien Brana, vice president of Infoclimat, a group that focuses on climate observation, told French newspaper Le Monde that his organisation first noticed a sudden and inexplicable rise in temperature at the Charles de Gaulle airport on April 6, when temperatures briefly rose to 22°C at 9:30 pm, before dropping back down to cooler spring temperatures.
“When the information came out, we all thought it was a sensor drift. Then, we suspected a maintenance problem,” Brana said, adding that the second occurrence on April 15 prompted some investigating.
It was soon revealed that the temperature anomalies coincided with unusually high winnings on Polymaket linked to bets on Paris temperature readings at the exact time of the abnormal readings. For example, an anonymous trader with the username “xX25Xx” bet $119 that the weather in Paris on April 15 would jump past the equivalent of 64 degrees Fahrenheit and won $21,398.
Météo-France said it filed a complaint with airport police about possible tampering with its equipment, and people have already started speculating that someone must have used a lighter or a battery-operated hair dryer to heat the station’s temperature sensor.
The weather forecasting service stated that “physical findings on one of our instruments and the analysis of sensor data” prompted its complaint.
French analytics firm Bubblemaps reported that no other weather station in the Paris area recorded the unusual temperature spike, and that xX25Xx’s bet that day was 20 times larger than their typical wager. Interestingly, the weather station at Charles de Gaulles Airport was the one used to track the temperature on Polymarket.
Polymarket has yet to comment on this situation, but its website shows that it is no longer using the Charles de Gaulle weather sensor data and is instead using data from a station at the Paris–Le Bourget Airport to settle bets.
