French authorities have launched an investigation into suspicious temperature spikes at Paris Charles de Gaulle International Airport that coincided with unusually large bets on the online prediction market Polymarket. The inquiry follows complaints from météo-France, the country’s national meteorological service, which suspects that a weather sensor at the airport was tampered with to influence weather-related wagers.
In early April, Ruben Hallali, CEO of the weather risk firm Sereno, received alerts about abrupt temperature increases recorded at the Charles de Gaulle station. On April 6, the temperature reportedly rose from 64 to 70 degrees Fahrenheit in minutes around 7 p.m., and on April 15, it climbed again sharply from 61 to 72 degrees between 9 and 9:30 p.m., before returning to previous levels. Both spikes set the daily high temperature—a key metric for bets placed on Polymarket.
These unusual measurements prompted météo-France to notify local police and prosecutors last week. Laurent Becler, a spokesperson for météo-France, confirmed the service’s complaint but declined further comment, citing the ongoing investigation. Officials at Charles de Gaulle airport and the airport police also refrained from commenting, while the Bobigny Public Prosecutor’s Office acknowledged the investigation but noted that no complaint had been filed against Polymarket itself.
Polymarket, a platform where users wager on diverse outcomes including weather events, reported nearly $1.4 million in bets on the Paris daily high temperature on the days in question. Some bettors received payouts totaling thousands of dollars, significantly above typical activity. Following the complaint, Polymarket shifted to using temperature data from a different site near Paris, the Paris-Le Bourget Airport.
Experts caution that such tampering not only undermines the integrity of prediction markets but could also pose risks to airport safety. Temperature readings are integral to calculating aircraft takeoff distances, climb rates, and frost treatments. Hallali described the incident as a reflection of vulnerabilities in data systems exposed to financial incentives.
Online speculation has included theories about how the temperature sensors might have been manipulated, such as by exposure to a hair dryer or lighter. Hallali suggested the precision of the April 15 spike indicated the possible use of a calibrated portable heating device but stopped short of confirming any specific method.
The case raises broader concerns about insider trading in prediction markets. Previous incidents on Polymarket have involved traders using classified or nonpublic information to bet on political events, including a U.S. Army Special Forces member charged for leveraging classified intelligence to place bets related to Venezuela.
As the probe continues, meteorologists and legal investigators are reviewing data and betting records to determine the full scope and intent behind the anomalous temperature spikes at one of Europe’s busiest airports.