French police are investigating whether someone tampered with a national weather forecasting sensor after a string of unusual temperature readings in Paris lined up with suspicious winning bets on Polymarket. The bets were settled using a Météo-France station at Paris’s Charles de Gaulle airport, where traders were wagering on the city’s temperature in March and the first weeks of April.
The sums were large enough to draw attention. On a few of the days, more than $500,000 was in play, and three separate wallets made more than $280,000 by betting that the temperature in Paris would reach 19C on 15 April. That day, the reading unexpectedly jumped by 5C in the evening, and at least one wager appears to have been placed just before the spike, producing a $21,000 profit for an anonymous user.
Météo-France told the Financial Times that physical findings on one of its instruments and the analysis of sensor data led it to file a complaint. French police confirmed they had received that complaint, and the cybercrime division is now investigating. Polymarket has since stopped using the Charles de Gaulle sensor as a pricing metric and switched to one at Paris-Le Bourget airport, but it did not cancel the contracts or refund the bets.
The episode lands at a sensitive moment for a platform that has become much bigger than a niche betting site. Polymarket is drawing attention from traders and institutional investors, including Goldman Sachs, who are starting to use its data to inform their trades. It also has investors including a venture capital firm owned by Donald Trump Jr., which has helped push the company further into the political and financial mainstream.
The concerns go beyond Paris. Bettors have discussed contacting the Institute for the Study of War, whose maps determine dozens of active bets on the flux of war on Ukraine’s frontlines, and one Israeli journalist was threatened after reporting a missile hit near Jerusalem because nearly $1m was staked on whether Iran would strike Israel that day. The fear in the market is simple: if thin trading can move odds and settle contracts, a small group with the right timing may be able to bend a bigger market around it.
That is why the French inquiry matters beyond one weather sensor. Polymarket has already faced scrutiny in other high-stakes corners of the site, including a Special Forces soldier arrested in a $400,000 Polymarket Maduro bet case and the surge of interest around Oilers Vs Ducks: Game 2 odds, where a bonus draw also drew attention. What happened in Paris now tests whether a prediction market can keep its contracts honest when the thing being bet on may itself have been nudged.
