Exactly 40 years ago, America’s most dramatic blackout ever hit New York City, and the city went nuts. On July 13, 1977, as Brooklyn’s poorest residents took to the streets to direct traffic, store owners set their own shopfronts on fire to optimize their insurance payouts after looting. That blackout, caused by damage to a couple of transmission lines at a nearby nuclear plant, lasted two days and caused unprecedented chaos.

It’s possible that the same could happen now — but on a global scale.

A blackout this intense could happen if our planet careens into the path of a massive solar storm. These happen all the time on a geologic scale, but one hasn’t yet occurred in the electrical era. As a species, we’re woefully unprepared for the moment when it does.

The last massive solar storm was on September 1, 1859, missing the era of global electrification by just a couple of decades. During the storm, the sun spit out a stream of plasma, white light, and electrons — a mere sliver of its total mass and energy — but that alone was strong enough to completely overwhelm Earth’s magnetic fields when it crashed into them just hours later. Even just eight minutes after the storm, an English 33-year-old amateur astronomer named Richard Carrington was trying to project sunspots onto a plate of glass when, as he later wrote, he thought “a ray of light had penetrated a hole in the screen attached to the object-glass … for the brilliancy was fully equal to that of direct sunlight.”

Carrington's drawing shows the bright, bean-shaped flares amid the sunspots, labeled A, B, C, and D. Harvard

The morning after what’s now known as the Carrington event, the sun’s electrons arrived and promptly found telegraph wires, causing power surges that shocked operators, set fire to papers in telegraph offices, and rendered man-made electricity useless in the machines they ran through. At the same time, red, green, and purple auroras lit up the skies as far south as the Bahamas. Even in cities where it was still night time, NASA states that “newspapers could be read as easily as in daylight.”

In 1859, there wasn’t any electrical infrastructure important or complicated enough to cause real problems, so the solar storm, though intense, came and went. But in today’s completely electricity-dependent society, we’re much more vulnerable.

Here’s NASA’s roundup of how smaller storms have disrupted life on Earth in the last few decades:

A huge solar flare on August 4, 1972, knocked out long-distance telephone communication across Illinois. That event, in fact, caused AT&T to redesign its power system for transatlantic cables. A similar flare on March 13, 1989, provoked geomagnetic storms that disrupted electric power transmission from the Hydro Québec generating station in Canada, blacking out most of the province and plunging 6 million people into darkness for 9 hours; aurora-induced power surges even melted power transformers in New Jersey. In December 2005, X-rays from another solar storm disrupted satellite-to-ground communications and Global Positioning System (GPS) navigation signals for about 10 minutes. That may not sound like much, but as [Bell Laboratories engineer Louis] Lanzerotti noted, “I would not have wanted to be on a commercial airplane being guided in for a landing by GPS or on a ship being docked by GPS during that 10 minutes.”

It’s difficult to calculate the extent of the damage a Carrington-scale storm could do to Earth today, but we can be sure that most of the human population would experience blackouts for far longer than New Yorkers did in 1977. On the Earth’s surface, the damages to the electrical grid — and the effects that would have on transportation, sanitation, medical, and even water infrastructure — would cost around $1 or $2 trillion in the first year, with four to 10 years necessary for a full recovery.

The storm would destroy the entire fleet of satellites in orbit, causing up to $70 billion in damage. Global telecommunications infrastructure would be destroyed so rapidly that humans wouldn’t even know — or be able to find out — that a solar storm had hit.

A modern solar flare recorded Dec. 5, 2006, by the X-ray Imager onboard NOAA's GOES-13 satellite. The flare was so intense, it actually damaged the instrument that took the picture. Researchers believe Carrington's flare was much more energetic than this one. NASA

The bad news is that we have no idea when the next Carrington event will happen. Our best guess is that a similar solar storm strikes the Earth about once every 500 years, but that’s based on very limited data. The fact is, like those New Yorkers in 1977, we’ll have no way to tell when the next big one is coming until it’s too late. Whenever it does hit, however, the world won’t be the same afterward.