“Most people would be surprised to know that even a very small regional nuclear war on the other side of the planet could disrupt global climate for at least a decade and wipe out the ozone layer for a decade,” study lead author Michael Mills, an atmospheric scientist at the National Center for Atmospheric Research in Colorado, told Live Science.

The researchers predicted the resulting firestorms would kick up about 5.5 million tons (5 million metric tons) of black carbon high into the atmosphere. This ash would absorb incoming solar heat, cooling the surface below.

The simulations hint that after such a war, global average surface temperatures would drop suddenly by about 2.7 degrees Fahrenheit (1.5 degrees Celsius), their lowest levels in more than 1,000 years. In some places, temperatures would get significantly colder — most of North America, Asia, Europe and the Middle East would experience winters that are 4.5 to 10.8 degrees F (2.5 to 6 degrees C) colder, and summers 1.8 to 7.2 degrees F (1 to 4 degrees C) cooler. The colder temperatures would lead to lethal frosts worldwide that would reduce growing seasons by 10 to 40 days annually for several years.