Months of mild weather lulled US and European gas traders into believing winter would bring more of the same-not the brutal freeze gripping much of America.

Their bad bet is now reverberating around the world.

Futures prices for natural gas – fuel for home furnaces and power plants alike-jumped 70% in the US over a wild week of trading, as forecasts for deep cold grew steadily worse. The previous week, prices rose 30% in Europe, where a cold snap combined with geopolitical jitters to drive up the market. Before the sudden surge, many traders on both sides of the Atlantic had been betting prices would fall instead. Nor is it certain that the worst of the run-up is over.

Temperatures in gas-producing parts of the US could drop low enough in coming days to freeze pipelines-potentially choking off supplies just as demand for the fuel soars. While the main futures market is closed over the weekend, some spot trading will continue. With that in mind, one trading team planned to spend Saturday and Sunday at a downtown Houston hotel to ensure backup power generation-and a stable internet connection to the Intercontinental Exchange trading platform -should blackouts sweep the region. “Everyone’s in panic mode right now,” said Paul Phillips, senior strategist for Uplift Energy Strategy, a Denver, Colorado-based gas trading firm. “People were writing off winter last week.”

The price spike-the most abrupt weekly increase on record in the US-illustrates just how integrated the country has become into the global gas market.

America’s emergence in recent years as the leading gas exporter means much of the world is now reliant on US supplies, making price volatility at home an international story.

Indeed, cold weather in Texas and other gas-producing states has helped drive prices so high that many smaller buyers in Asia may no longer be able to pay, with liquefied natural gas tankers likely sailing to Europe instead.