Living on Sea Ice: A Vital Habitat Under Threat

Emperor penguins breed on sea ice, which is the frozen surface of the ocean. These birds are specialized to survive in cold conditions that would be too harsh for humans. Emperor penguins have some specific requirements. If there is not enough sea ice, they do not have a place to live. If there is too much sea ice, they have a long walk to get to the open ocean, where they hunt for food for themselves and their chicks. So, the sea ice must be just right for emperor penguins to live, get food, and raise their chicks (Figure 1 and Video 1).

We know the world is getting warmer and that there might be less sea ice for emperor penguins in the future. The world is warming because humans are producing greenhouse gasses (such as carbon dioxide) that trap the sun’s heat near the Earth. Greenhouse gasses come from human activities such as burning oil, gas, and coal. The faster the world warms, the less likely emperor penguins are to have sea ice. Will Emperor penguins march to extinction?

Surviving the Unimaginable

About 250 years ago James Cook, a captain in the British Navy, was sailing around the world. He and his crew may have been the first people to see emperor penguins. What we know for sure is that later, someone noticed that emperor penguins were a different species than king penguins [1]. In the early part of the 1900s, Robert Falcon Scott, another captain in the British Navy, sailed to Antarctica. He found the first rookery of emperor penguins. Now, using pictures of the world taken from satellites in space, we know that there are 61 colonies of emperor penguins in Antarctica [2].

Even though we have been studying emperor penguins for about 100 years, we still have a lot to learn. These penguins live in dangerous places, and that makes them hard to study. But that has not stopped people from trying. Around 70 years ago, two famous scientists, Bernard Stonehouse and Jean Prévost, visited Antarctica to study emperor penguins. These scientists learned how important sea ice is to these penguins [3]. In the winter when it gets cold, the surface of the ocean freezes. These icy spots on the sea are where emperor penguins gather in special groups to take care of their baby chicks. Those areas are called rookeries or colonies. After forming colonies, the emperor penguins choose their mates in March/ April. The females lay one egg each in May or early June, and the males keep the eggs warm by holding them on the tops of their feet. Males do this for nearly 3 months—and it is not easy! Wintertime in Antarctica is dangerously cold and stormy—temperatures can get down to -50°C, and winds can blow at over 150 km per hour. The males must huddle together to keep warm and to survive. The penguins take turns being in the middle of the huddle, where temperatures can reach 37°C. The penguin dads keep the eggs warm and cozy while the mommies search for food (Figure 1).

When the females have eaten enough squid, fish, and krill (shrimp-like creatures), they come back to feed the newborn chicks. The males, which have not eaten in 4 months, are starving by this time. The females take over keeping the chicks warm, while the males search for their own food. Then, mommy and daddy penguins take turns feeding their chick, so the chicks grow up fast and strong. In early spring, the chicks are twice as big as when they hatched, and they can be left on their own. Chicks huddle together to keep warm and to defend each other against other birds species that might attack them, while the parents search for food for a few days at a time. It is hard work raising an emperor penguin chick! Chicks must grow enough to get their waterproof adult feathers before the sea ice melts away for the year. The soft, fluffy feathers the chicks have when they are born are not waterproof, so if chicks get wet, they can freeze. From early November, chicks begin to get their adult feathers, and they leave the colony in early summer, from December to January. Without their parents, the chicks hang out together on the ice.

Troubling Trends

Even though emperor penguins are difficult to study, we have a few clues from a colony found at Pointe Géologie, where they have been studied for a long time. This is where the movie March of the Penguins was filmed! There is a mystery at Pointe Géologie. In the 1970s, the number of emperor penguins decreased from about 12,000 birds to about 6,000 birds [4]. Scientists think that many of the adults were dying, and the sea ice was a clue to this mystery. More males died when there was not enough sea ice. Emperor penguins eat animals that live under the sea ice (fish, squid, and krill), and less sea ice probably meant less food. Males need more food than females because they go without eating for 4 months during winter.

Another mystery is that the population of emperor penguins at Pointe Géologie has not yet returned to 12,000 birds. Scientists observed that, in years with too much sea ice, fewer chicks survived. Too much sea ice means penguins must travel longer distances to reach open water, where they can find food. So, there is a sea-ice “Goldilocks zone.” Too much sea ice means adults take too long to get food, so both adults and chicks may starve. Not enough sea ice means less food for penguins, and chicks may not grow their waterproof feathers before the sea ice melts away.

Today, Antarctica is changing because of greenhouse gasses. Warmer temperatures around the world will cause the sea ice to melt and break up earlier in the spring. Scientists have created computer models to see what would happen to emperor penguin populations if these penguins have less ice to live on. If we do not change the way we make and use energy, penguins at Pointe Géologie will be at risk of extinction by 2100 [5].

Scientists want to see what will happen to all other emperor penguin colonies, too. Some colonies, such as those in the Ross Sea, might be OK in the future because sea ice declines are less severe at those locations. Sadly, if we continue to put greenhouse gases into the air, all emperor penguin colonies will probably decrease by the year 2100 (Figure 2). If we keep warming the air, the temperatures around the world will be much higher than we want them to be (increase of 4.3°C above the temperature in 1850), and most emperor penguin colonies will disappear. If we can limit global warming to only 1.5°C, emperor penguins will still exist in Antarctica by 2100.

Recently, scientists wondered what would happen to emperor penguin colonies if extreme weather events happened. For example, at Halley Bay (Figure 3a), an estimated 10,000 chicks or more died in one year because of very low sea ice. Halley Bay was the world’s second- largest emperor penguin colony before this extreme event. Scientists can observe these rare extreme weather events using satellites. At Halley Bay, such satellite images showed that, in 2016, the sea ice broke up early, before the chicks could swim (Figures 3b–d). By better understanding how extreme weather events affect penguins, scientists now think that 98% of colonies will be disappear by 2100 if we do not control greenhouse gas emissions—this means that almost all the emperor penguins in the world will be gone. Emperor penguins will only stand a chance if greenhouse gas emissions are slowed from their current course.

Satellite images have also helped us understand how colonies might change as penguins move from one spot to another. Does moving between homes mean penguins could find new places to live as the sea ice melts? Scientists initially thought that penguins might leave places that were not good homes and would search for better locations so they could survive. But sadly, it seems that moving between homes does not help, and emperor penguins will still face a risk of extinction if we do not stop releasing greenhouse gasses [5].

Living on Thin Ice

Emperor penguins cannot change the way they live fast enough to deal with climate change. So, to save them, humans should reduce greenhouse gas emissions. If we can keep the increase in air temperature around the world to <1.5°C, emperor penguins will have a better chance of surviving. In 2015, people from 195 countries met in Paris, France and agreed to limit global warming to well below 2°C. This meeting led to a legal document known as the Paris Agreement. This agreement represents the first time that all nations have joined the common cause to fight climate change. Governments must take actions now to reduce greenhouse gas emissions, to protect the Earth and its species for today’s and future generations [6]. You can find out more about whether governments are meeting the 1.5°C Paris Agreement by looking at the Climate Action Tracker.

Climate change affects everyone. Today, emperor penguins serve as a signal to show us whether we are effectively controlling greenhouse gas emissions. They can tell us if we are in danger. We are all on thin ice. The future of emperor penguins, humans, and all other life on Earth as we know it depends upon the decisions we make today.

Glossary

Sea Ice: ↑ Sea ice is frozen water that forms on the surface of the ocean. It is like a big icy blanket that covers parts of the sea when the weather gets really cold. Sea ice is important because it gives some animals a place to rest and hunt, and it also affects the weather and the whole Earth’s environment.

Greenhouse Gasses: ↑ Gasses like carbon dioxide that trap the sun’s heat in Earth’s atmosphere, like a blanket of gasses that surrounds our planet and heats it up.

Extinction: ↑ The end of a species’ existence on Earth. Once a species becomes extinct, no more individuals exist and it is gone forever.

Rookery: ↑ A breeding colony or nesting area of birds, particularly seabirds. It is a location where birds gather in significant numbers to build nests, lay eggs, raise their young (chicks), and engage in various reproductive activities. The term is commonly used in the context of penguins, seals, and other marine birds and mammals.

Colony: ↑ Animals living together for mutual benefit, such as stronger defense against predators. For emperor penguins, living in colonies is a great defense against the cold and wind.

Computer Models: ↑ Computer-based versions of a natural system, which scientists can use to understand the system and the way that various factors might change the system in the future.

Extreme Weather Event: ↑ Any occurrence of rare, severe weather that is outside of normal weather patterns. Extreme events can cause devastating impacts on communities and ecosystems.

Paris Agreement: ↑ A plan to reduce greenhouse gas emissions to limit the average global temperature increase. It was signed by 195 nations that agreed to the importance of fighting climate change.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

This work was supported by the NSF- OPP # 2037561 and NASA # 80NSSC20K1289.