When the scientists removed topography like mountains from the model, the Northern Hemisphere got stormier, decreasing its difference in storminess compared with the Southern Hemisphere by about half. Ocean circulation mattered, too: When it was removed from the model, it also halved the difference between hemispheres.

The study also offers an explanation for the increase in Southern storminess since the beginning of satellite observations in the 1980s.

As carbon dioxide in the atmosphere increases, so does sea ice loss and sea surface temperature in the Northern Hemisphere. This effect cancels out changes in northern oceans, the researchers write. Meanwhile, the ocean currents that drive storms don’t change in the Southern Hemisphere because its sea ice isn’t melting at the same rate as CO2 levels rise. This helps drive the resulting imbalance between storminess in the North and South.

Overall, the researchers found that the Southern Hemisphere is 24 percent stormier than the Northern Hemisphere on average.

In a news release, study author Tiffany Shaw, a climate scientist at the University of Chicago, says understanding the difference in hemispheres will help researchers as human-caused climate change speeds up.

“By laying this foundation of understanding, we increase confidence in climate change projections and thereby help society better prepare for the impacts of climate change,” she says.

Researchers predict that as climate change continues worldwide, extreme weather events will increase as well.