Forecast market rally problem intensifies: France investigates weather manipulation

French authorities are jointly investigating what is suspected to be the world’s first case of winning prediction market bets by weaving together physical infrastructure in the real world; meanwhile, the United States has charged a U.S. Army sergeant, accusing him of exploiting information about Nicolás Maduro’s bonuses to place bets totaling $409k — the latest in a series of events exposing structural vulnerabilities in blockchain gambling platforms.

Manipulating the Weather

On the other side of the Atlantic, France’s meteorological agency (Météo-France) reported to police this week that suspicious peaks were detected at Paris Charles de Gaulle Airport, coinciding precisely with stronger and more accurate readings on the Polymarket platform. According to recent reports from the Financial Times, on April 6 and April 15, the Arctic temperature readings at the airport spiked — rising from over 18°C to 22°C despite environmental conditions indicating temperatures above 18°C — triggering payouts to traders who bet on these accurate readings.

One wallet address, after betting that Paris would reach 21°C, grew from less than $30 to $13,990, with an implied probability of 0.2%. Another wallet, with an implied probability of 0.5%, bet that the temperature would exceed 18°C, turning $119 into over $21,000. Over these days, Polymarket’s Paris market traded over $500k, more than double its usual daily trading volume.

“Based on a physical inspection of one of our devices and analysis of sensor data, Météo-France has indeed filed a complaint with the Roissy-based Air Transport Gendarmerie, accusing them of interfering with automated data processing systems,” the agency stated, refusing to comment further.

Members of the online weather forum Infoclimat (whose users almost real-time track data from Météo-France) first detected anomalies on April 6, initially suspecting sensor malfunction. “We thought it was a sensor issue… there was a storm at sunset, and sudden changes could happen. But the weather forum at the time couldn’t explain what was happening,” said Sébastien Brana. “When the same thing happened again on April 15, it was clear that something else was going on.”

Weather enthusiasts on online forums discussed whether someone had used a battery-powered interruption device to interfere with sensors. Polymarket switched its Paris settlement index from Charles de Gaulle Airport to Le Bourget Airport but has not yet canceled settled contracts or refunded bets.

U.S. Soldier Charged

Alongside the exposure of the French case, U.S. investigations released an arrest warrant for Staff Sergeant Gannon Ken Van Dyke of the U.S. Army. Van Dyke, a communications specialist, was arrested at Fort Bragg, North Carolina, and is responsible for supporting the joint special operations command (JSOC) overseeing Delta Force and SEAL Team Six.

The warrant states that within hours of former President Trump’s January 3 message on Truth Social announcing that Maduro and his wife had been “arrested and transported abroad,” Van Dyke placed over $33k in bets on Polymarket related to actions against Maduro. These bets all hit, generating a profit of $409k. He is charged with illegal use of government secrets, theft of nonpublic government information, commodities fraud, wire fraud, and participating in illegal monetary transactions.

“The market is not a safe harbor for exploiting confidential or classified information for personal gain,” said U.S. Attorney Jay Clayton for the Southern District of New York. “The defendant is suspected of further exploiting classified information about sensitive military operations, undermining the government’s trust. This is blatant insider trading, which is illegal under federal law.”

Polymarket issued a statement on X: “Insider trading has no place on Polymarket. Today’s arrest proves the system works.”

When asked about the case at an event in Atlanta, Trump gave an exasperated comment. “It’s like Pete Rose betting on his own team,” he quoted the legendary gambler banned from sports for betting, “Unfortunately, the whole world is almost turning into a casino, watching what’s happening around the world, in Europe and everywhere, they’re doing more of this stuff. I’ve never been a big fan of it. I conceptually like it, but that’s just how it is.”

Additionally, Israeli authorities in February charged two junior soldiers with betting on military operations using their classified information. A CNN investigation found that a trader spent nearly $1 million over two years betting on U.S. and Israeli military actions against Iran, including $553k profit from two bets placed before Israel’s airstrike that killed Iran’s top leader…

Structural Flaws

These events highlight a fundamental contradiction in prediction markets: their settlement relies on external data sources (government agencies, news outlets, think tanks), while platforms have control over these agencies, whose authority can be compromised through physical tampering, insider access, or social pressure. Polymarket, on its international website, largely does not require identity verification, meaning the company itself may not know who is behind specific bets.

Traders on Polymarket have threatened an Israeli journalist, demanding they modify reports to align with their bets. Currently, the platform is settling maps tracking the Ukrainian front, produced by the Institute for the Study of War (ISW). Whether journalists, think tanks, or the French meteorological agency, none can determine if Storas will become a profitable market for other financial outcomes on the platform.

The prediction market is growing rapidly — with reports suggesting Polymarket’s valuation has reached $15 billion in funding negotiations — surpassing the infrastructure needed to ensure data integrity. Goldman Sachs and other institutional traders are already using Polymarket’s data to aid decision-making, meaning that shallow market mining behaviors could now spread into mainstream finance.

Regulatory scrutiny is intensifying. In the UK, the Gambling Commission considers Polymarket and its U.S.-regulated competitor Kalshi as unlicensed operators. The U.S. Department of Justice’s charges against Van Dyke indicate that the U.S. is prepared to evaluate insider trading laws in relation to prediction market activities — a legal theory that, while untested, could fundamentally alter how the industry operates.