If we don’t cut greenhouse gas emissions to address climate change, then by the end of the century, 70 percent of king penguins could face a tough decision: either find a new home or die, according to new research.

King penguins live on islands scattered throughout the Southern Ocean, the waters surrounding Antarctica. The birds can swim as far as 310 miles (500 kilometers) to feed on lanternfish, squids, and krill in a food belt circling the continent. But climate models show that this food belt will move closer and closer to the South Pole, forcing the penguins to swim farther to catch their meals. By 2100, the penguins are expected to migrate to other islands or as many as 70 percent of them could disappear, according to a study published today in Nature Climate Change.

“Wow,” says Michelle LaRue, a research ecologist at the University of Minnesota, who was not involved in the study. “That’s not something I would have expected.” Unlike their closest relatives, the emperor penguin, king penguins don’t live on sea ice. In fact, they only live on ice-free islands. So in a warming world, you’d expect penguins that don’t need ice to breed to fare just fine, LaRue tells The Verge. But today’s study shows that the cascading effects of climate change are incredibly complex and can affect species in a variety of ways.

For king penguins, the future is bleak. “We know that penguin populations will collapse soon,” says study co-author Céline Le Bohec, an ecologist at the Hubert Curien Multi-disciplinary Institute in France, in an email to The Verge. “They are showing us the tip of the iceberg of what is happening in the ecosystems.”

Today, there are an estimated 3.2 million breeding adult king penguins in the world that are not currently vulnerable to extinction. The biggest colonies exist on the Crozet Islands, an archipelago halfway between Madagascar and Antarctica. During the summer, these penguins swim between 186 to 310 miles (300 to 500 kilometers) to find their food, at times staying at sea for months, Le Bohec says. The birds feed in a particularly rich band of water circling Antarctica, called the Antarctic Polar Front. Here, cold waters meet warmer waters from temperate regions, sustaining a bloom of marine life, from plankton to krill to fishes. The king penguins depend on this food to survive.

But the Antarctic Polar Front is expected to change as the world keeps warming up. As ocean surface temperatures go up, this food belt surrounding Antarctica will move closer to the South Pole, says study co-author Emiliano Trucchi, a researcher at the Università degli Studi di Ferrara in Italy. This will force king penguins to swim farther to forage: birds living on the Crozet Islands, for instance, will have to swim about 435 miles (700 kilometers) to reach the Antarctic Polar Front. That will require more energy from the adults, and it will mean less food for the chicks waiting at home, putting the penguins at risk. “It seems that for this archipelago, there’s not much hope in the future,” Trucchi tells The Verge.

By coupling climate projections with genomic and environmental data, Trucchi, Le Bohec, and their colleagues found that half of the world’s king penguins will lose their habitat completely, such as on the Crozet and Prince Edward islands. And 70 percent of king penguins — around 1.1 million breeding pairs — will either have to move to other islands or they will disappear by the end of the century. “I’m worried about the future of the species,” says Le Bohec.

Relocating for king penguins is complicated. Because they live only on ice-free islands that are around 32 degrees Fahrenheit (0 degrees Celsius) year round and breed on sandy or pebbly beaches, finding a new home is hard. The mass migration could mean that king penguins will get into a competition for space and food with other penguin species, Trucchi says.

The way to avoid all this mess — and the extinction of many more species — is obviously to tackle climate change by reducing emissions of heat-trapping greenhouse gases. “It’s important to take action, to try to do something,” Trucchi says. “It depends which kind of Earth you want to live on in the future: empty or full of nice species around us.”