Emperor penguins like it cold. Now, scientists have determined that the penguins’ susceptibility to climate change accounts for a dramatic decline in their number over the past half century.

Over the past 50 years, the population of Antarctic emperor penguins has declined by 50 percent. Using the longest series of data available, researchers have shown that an abnormally long warm spell in the Southern Ocean during the late 1970s contributed to a decline in the population of emperor penguins at Terre Adelie, Antarctica.