Texas had a rough winter in 2021.

In mid-February, with temperatures dropping to the single digits, demand for electricity hit a record high throughout Texas. Supply ran short, causing the state’s electric grid operator to implement rolling power outages. At the height of the crisis, more than 4.5 million customers lost power. The freak winter storm caused neighboring states such as Louisiana, Oklahoma, Arkansas and Kansas to also impose rolling blackouts.

Texas residents shivered in the cold, as outages lasted for days at a time. They lost access to water. Some resorted to turning on their cars in their garages to keep warm then died due to carbon monoxide poisoning.

The historic breakdown was a wake-up call — if the power grid in Texas was so fragile, what about the rest of the United States? The U.S. has faced a 67% increase in weather-related power outages since 2000, according to data from Climate Central. Part of the problem is an aging infrastructure. Most of today’s power grid was built in the 1950s and ’60s, with the hopes that it would last for 50 years.

Watch the video above to find out what happened in Texas’ power outage and how it’s a warning sign for the U.S. power grid.