Vitalik Buterin Urges Polymarket to Use Median Data After Paris Weather Manipulation

Vitalik Buterin said on April 23 that prediction markets such as Polymarket should use the median of at least three independent data sources rather than relying on a single external feed. His comments followed reports tied to a Polymarket Paris weather market in which temperature readings at Paris Charles de Gaulle Airport briefly spiked by more than 3 degrees Celsius within minutes on April 6 and April 15 before falling back. Le Monde reported the anomalies and Météo-France filed a criminal complaint. A circulating video and reports of repeated winning bets fueled claims that a sensor may have been heated with a hair dryer to influence settlement. Reported profits differ between accounts: one says an anonymous trader made about $34,000, while another says two traders won a combined $37,000. The episode highlights how blockchain-based prediction markets remain vulnerable when settlement depends on potentially manipulable offchain reference data.