The blackout caused chaos for tens of millions of people. It shut down traffic lights and ATMs, halted public transport, cut phone service and forced people to eat dinner huddled around candles as night fell. Many people found themselves trapped in trains and elevators.

Spain’s prime minister, Pedro Sánchez, has said the exact cause of the blackout is yet to be determined. In early reporting, Portugal’s grid operator REN was quoted as blaming the event on a rare phenomenon known as “induced atmospheric vibration”. REN has since reportedly refuted this.

But what is this vibration? And how can energy systems be improved to mitigate the risk of widespread blackouts?

How much does weather affect electricity?

Weather is a major cause of disruptions to electricity supply. In fact, in the United States, 83% of reported blackouts between 2000 and 2021 were attributed to weather-related events.