You Switched the Lights On. Traders Made Billions of Dollars.

Before dawn on a recent autumn day, fog set in over large swaths of eastern Europe. In any other financial market, the weather wouldn’t have mattered much. Perhaps a few delayed flights, maybe some traffic jams, most of little consequence. But in Europe’s electricity bazaar, bad weather equals money.

More than 1,000 kilometers away from the fog, a small group of largely anonymous trading firms based in Denmark was ready to pounce. As soon as the infrared picture from a Meteosat weather satellite arrived at their headquarters, computers automatically dissected it, feeding the data into complex trading algorithms.