James Titcomb
French police are investigating suspicions that a hairdryer may have been used to tamper with official weather readings to make thousands of dollars in Polymarket bets.
Temperature readings at Paris’ Charles de Gaulle airport have unexpectedly spiked twice in the past month, reaching levels much higher than expected.
On both days, gamblers on Polymarket, the world’s biggest prediction market, appear to have made huge sums by betting on unlikely weather patterns. The site relied on readings from the Charles de Gaulle temperature sensor.
Météo-France, the country’s official weather agency, said it had complained to police after noticing a change to one of its temperature sensors.
“In view of physical findings on one of our instruments and the analysis of sensor data, Météo-France was indeed led to file a complaint for alteration of the operation of an automated data processing system with the Air Transport Gendarmerie Brigade of Roissy,” a spokesman said.
“As the investigation is ongoing, we do not wish to make any further comments in order to ensure the proper conduct of the procedure.”
On April 6 and April 15, temperatures at the airport’s weather sensor unexpectedly spiked late in the day, with the peak temperature reading significantly higher than forecast.
On April 6, the sensor recorded a peak temperature of 21 degrees at 7pm and on April 15, the peak temperature of 22 degrees was reached at 9:30pm.
On both days, the peak temperature had hovered around 18 degrees during the day.
Polymarket, where people can use cryptocurrency to bet on thousands of different markets from politics to war, ran a daily market on the peak temperature in Paris using the airport weather station.
On both days, the markets put the chance of a 21 degree or 22 degree day at less than 1 per cent, meaning people who bet on the outcome earlier in the day would have made a substantial return on their initial stakes.
On April 15, one trader made $US21,000 ($29,400) betting that the maximum temperature would not be 18 degrees, data from Polymarket show. A temperature of 18 degrees was seen as a 99.6 per cent probability before the temperature spiked later in the day.
Successful bets on the temperature reportedly netted around $US34,000 ($47,600).
While it is unclear how the temperature might have been manipulated, one possibility shared on weather forums was that a battery-powered hairdryer could have been used, according to Le Monde newspaper.
The station is on a public road, making it easy to access.
The French Air Transport Gendarmerie and Polymarket were contacted for comment.
There are no indications so far that the successful punters have had to return their winnings. However, the data source for Paris’s hottest temperature has since moved to a sensor at the smaller Paris-Le Bourget airport.
