Near Paris-Charles de Gaulle Airport, a weather sensor recorded strange temperature spikes that no other stations in the region matched. On April 6, the temperature climbed about four degrees Celsius in twelve minutes. Nine days later, it spiked again to approximately 22°C, four degrees warmer than neighboring sensors.
Someone was betting on these exact spikes. Polymarket, a cryptocurrency prediction platform, allows users to bet on real-world events using external data feeds called oracles. For Paris temperature contracts, the oracle was the Charles de Gaulle weather station. A Polymarket trader won around $14,000 on April 6 and roughly $20,000 on April 15, totaling approximately $34,000 in suspicious winnings.
Online traders and meteorologists suspect someone used a battery-powered hair dryer to heat the sensor. The Charles de Gaulle station sits near a public road with minimal security, making it accessible to anyone with a travel hair dryer.
On April 23, France's meteorological agency, Meteo France, filed a criminal complaint. The suspected tampering carries serious penalties: up to seven years in prison and a €300,000 fine, since Meteo France is a public institution.
Polymarket switched its Paris temperature data source to Paris-Le Bourget Airport on April 19. This incident highlights the "oracle problem" in cryptocurrency: blockchains cannot see the real world and depend on outside data that can be manipulated.