Prediction markets have become a police matter in France, as the country's weather service called in the authorities after spotting what looks suspiciously like tampering by a Polymarket punter.
Météo France had filed a complaint after unusual temperature spikes were recorded over several days at Charles de Gaulle, including a jump of 5C in the space of a few minutes on April 15, according to reports from broadcaster French BFMTV, picked up by Bloomberg.
Officials said the data looked manipulated and technicians were sent to inspect the site, as meteorologists stressed that the temperature readings are important for pilots and air traffic controllers to manage take-offs, landings and flight paths.
Data from the thermometers also happens to be used to settle bets.
On Polymarket, traders bet on the day’s highest temperature using Météo France data.
On April 6, a newly opened account reportedly turned less than $30 into nearly $14,000 betting on a 21C reading, a move priced at just 0.2% probability, the Financial Times reported.
Days later, another trader made over $21,000 from a $119 stake on a similar long shot.
Soon after, Polymarket switched its temperature data reference to Le Bourget railway station.