The Carnegie scientists, Anna Possner and Ken Caldeira, suspected that drag like this might be far lower over water than over land, particularly in mid-latitude oceans in both the Northern and Southern hemispheres. Why might that be? As Earth tilts away from the sun each autumn, jet stream-like rivers of air form high in the atmosphere. Over the open ocean, storms pull these strong winds down near the planet’s surface, replenishing the wind energy captured by turbines.

The effect might sound small, but it adds up. The scientists calculate that a wind farm in the middle of the North Atlantic would generate at least twice as much energy — and perhaps three times as much — as an identical wind farm in Kansas, itself one of the windiest states in the U.S. A wind farm roughly twice the size of Alaska could generate 18 million megawatts of electricity. That’s enough to meet the entire global demand today.

There are big practical challenges to building such a farm, including coping with extreme mid-ocean weather and transmitting the power back to shore. And by harvesting so much wind in the North Atlantic, a giant wind farm would reduce the output of onshore wind turbines in the U.K. and Western Europe — and reduce temperatures in the Arctic by more than 20 degrees. This might sound attractive at a time when polar ice is melting, but scientists worry about the unforeseen consequences of such geoengineering.