Traders are piling into bearish bets on US natural gas, wagering that a powerful El Niño will keep temperatures mild and curb heating demand this winter. A burst of Arctic cold risks upending the trade.

The ocean-heating phenomenon is expected to make winter warmer overall. Yet a BloombergNEF analysis found that sudden cold snaps linked to Arctic winds tend to occur more often during El Niño events. And meteorologists say the potential for disruptive outbreaks is building, particularly from January 2027.

Cold temperatures earlier this year showed how abruptly the market can tighten. A brutal freeze in January knocked out 10% of US gas production, lifted demand by 20% and sent prices for near-term physical deliveries at Henry Hub to a record high.

Money managers now hold their largest net-short position since the Covid-19 pandemic. As of Oct. 9, the latest date for which Commodity Futures Trading Commission data was available, money managers held a combined net-short position of more than 140,000 contracts across seven US gas benchmarks. That was the biggest bearish position since March 2020. It also marked a sharp break from recent history: Money managers were net long for 87% of the past five years.

The positioning reflects widespread expectations for a warm winter. January futures at Henry Hub are currently trading about 10% below their level last fall. If “the full blowtorch warmth” anticipated by many traders materializes, it could push late-winter gas futures contracts even lower, said Eli Rubin, senior energy analyst at EBW Analytics Group.

“If forecasts diverge in even a modestly colder direction, however, the massive speculator short position may be caught off guard and forced to buy back natural gas to cover positions — catalyzing a short squeeze,” Rubin said.

The danger isn’t necessarily that the entire winter turns cold. Even a brief Arctic outbreak can sharply lift heating demand, disrupt gas production and trigger a price spike.

“It does feel like there’s a little bit of complacency” in how gas traders are positioning ahead of winter, said Ben Smith, founder of energy analytics firm Enercast. “Even though it looks like it’s not a major concern, you still have these cold snaps that can easily spike the prices short-term.”A cold-driven price spike would also threaten the relief the US government expects for millions of households this winter. The Energy Information Administration forecasts that homes heated primarily with natural gas will spend an average $640 on the fuel from November through March, 9% less than last winter, largely because of lower prices. Natural gas is the main heating fuel for 46% of US homes.

The weather risk is harder to pin down. Traders use forecast models and longer-range climate predictions to shape their positions, but sudden cold shocks are notoriously difficult to predict in detail more than a few weeks ahead.

El Niño tends to favor sudden stratospheric warming events, which can break down the polar vortex and send deep, persistent cold into Europe and Asia, according to Judah Cohen, director of seasonal forecasting at the Atmospheric and Environmental Research JANUS Research Group. Less frequently, that sustained cold may grip parts of the US and Canada.

Cold can also wreak havoc on gas infrastructure. Water can freeze inside wellheads, rendering them inoperable. A combination of “freeze-offs” and preventive shut-ins squeezed US supplies during the severe storm that struck in late January 2026.

Consumers ultimately absorbed some of the cost. Dominion Energy Virginia passed more than $1 billion in deferred fuel expenses on to ratepayers, with more than $500 million of the projected balance incurred in January “as a result of the extremely cold and prolonged winter,” the utility told state regulators earlier this year. Dominion Energy Virginia did not respond to a request for comment.

The market may have fewer escape valves this winter. Power plants can switch from gas to oil when gas becomes too expensive, but tight diesel supplies have pushed futures to their highest levels ever for early October. Gas would have to climb much further before switching fuels becomes economical.

New England faces a similar constraint. The region imports liquefied natural gas during severe cold when its pipelines are full, but LNG prices are hovering near their highest levels since the Russia-Ukraine war began. That raises the threshold at which buyers can economically switch away from pipeline gas.

El Niño, in theory, should make the broad winter outlook easier to forecast, according to Bradley Harvey, lead forecaster at Vaisala Xweather. But there is no historical precedent for an event this strong colliding with human-caused climate change and a record-breaking ocean heat wave, which may alter some of its effects.

“We’re basing a forecast on whatever’s closest to where we are right now,” Harvey said, adding that clients continue to press for details on potential periods of extreme cold to gain an edge: “What does it take to get those days, so we can capture them first?”