Did someone interfere with the weather instrumentation at Charles de Gaulle airport to win large bets through Polymarket? On the evenings of the 6th and 15th of April, temperatures recorded by a sensor located at Paris-CDG airport rose abnormally. Suspicions were aroused when an online account won tens of thousands of Euros on high temperature betting for Paris on both days.
Infoclimat temperature data from Paris CDG 2026
There has been an unsubstantiated mention of a hairdryer being used, which has since be widely repeated in newspaper headlines. Surely that would need to be plugged in and would arouse attention? Questions about access and placement of the weather enclosure will be popping into the minds of amateur sleuths. And there is the case of the 2018 ice cream van at Strathclyde Country Park, Scotland.
Paris-CDG is a huge airport, which extends over 12.5 square miles. London Heathrow, by comparison, covers 4.7 square miles as the UK’s largest airport. There will be vast open areas and long runways but you can’t wander around an airport field without proper access. Nowadays, most temperature reporting is done remotely, the sensors send the data in real time. Gone are the days of an observer taking the readings each hour, although there are many sites that are still checked at least once a day.
Trained weather observers know not to keep the Stevenson screen louvred door open for long, to avoid altering the shaded air inside. The white door also opens to the north, to avoid direct sunlight falling on the thermometers or sensors. The distilled water for the wet-bulb thermometer in the screen needs to be checked every few days for humidity readings, and there will often be a rain gauge and sunshine recorder at the same site. People will need access, but at an airport, it shouldn’t be just anyone and even in local parks, the enclosures often have fencing. Infoclimat thought that there had been ‘sensor drift’ and assumed that it was a maintenance issue.
Infoclimat photo of Roissy CDG
What has been reported ‘near a public road with almost no fencing or cameras’ from a physical inspection Météo-France conducted after the incident.
Which reminds us of a UK incident in late June 2018. A well-established Glasgow observation site recorded 31.9C. On the same day, a temperature observation appeared from Strathclyde Country Park near Motherwell of 33.2C, which would have passed the temperature record for Scotland in June (32.2C), and all-time record of 32.9C. It had to be checked out.
It appeared that a "vehicle" parking nearby could have been responsible for a spike in the temperature reading. An often-present ice cream van seems to have been the culprit but overall clutter, tarmac and general chaos called the whole site into question as a reliable observation site.
In Paris, could a vehicle draw up near to the sensor and direct its exhaust for five minutes before driving away? It might not attract as much attention as pointing a hair dryer towards the airfield.
Meteo France, the national meteorological service, has raised a complaint with the air transport gendarmerie in Roissy. Questions are being asked, not only about the likely brazen manipulation related to online betting but also about the interference with scientific equipment.
There is a valuable network of observation points across Europe and around the globe. This is vital data to monitor our weather and climate, it feeds into the computer forecast models, and it helps with logistical airport processes, when the weather gets very hot or very cold. The suggestion that someone managed to artificially heat the air near the sensor, not once but twice, to manipulate the outcome of a bet has to be worrying for the whole observation network.
A Polymarket customer placed successful bets on unusually high temperature spikes in Paris on two separate occasions in April. On 6th April, before 7pm (so this is late in the day), temperature readings at CDG rose suddenly to 22°C before dropping back down. The temperature rose 4C in 12 minutes but only at that site. Conditions in other Paris regions did not change and there was no accompanying shift in wind direction or humidity to accompany the CDG rise in temperature.
It is usual practice for weather forecasters to compare readings across an area and discount known erroneous readings or investigate oddities. This happens for record-breaking temperatures with the UK Met Office investigating or the WMO (World Meteorological Office) in a thorough verification process, which can take months or a year. Like after a horse race when there is a stewards' enquiry but more scientific.
The forecast for Paris had been 18C but there was an aggressive Polymarket bet on readings above 21°C on the 6th. After a reported win of 12,000 euros, another anomalous spike occurred a week later, again at CDG with another big win for the same online user, around 17,000 euros. On 15th April, the sensor reached 22C but this was even later in the evening and so more suspicious, with a sudden spike up to 22C before falling away quickly.
“Polymarket is the world’s largest prediction market, allowing you to stay informed and profit from your knowledge by betting on future events across various topics.” Their own quick overview- on Polymarket, you can buy and sell shares representing future event outcomes.
A 'prediction market' is a relatively new term attached to emerging business models in the United States. A prediction market is a platform which enables participants to trade event-based contracts on markets, including financial, sports, and political events.” Gambling Commission UK
Polymarket is considered to be unlicensed gambling in France and there is a geo-block in place, as there is in the UK. It does not possess a gambling license from the UK's Gambling Commission. Essentially, people are creating their own bets and as it seems in this case, altering the natural outcome. Some might say this has been going on for centuries with animal racing and sports match fixing. More recently, blatant bets about invasion and missile timings in the Middle East and oil prices, never mind insider trading on the stock market.
Polymarket has now changed away from the CDG sensor to Paris Le Bourget Airport to resolve their Paris temperature markets.
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