Standing four feet tall and weighing up to 100 pounds, emperor penguins are the largest penguin species in the world. They are also incredibly vulnerable to climate change.

A recent study published in Global Change Biology by Stephanie Jenouvrier, associate scientist and seabird ecologist at Woods Hole Oceanographic Institution, and colleagues found that if humans are able to limit Earth’s temperature increase to 1.5 or 2 degrees Celsius above pre-industrial levels, there is hope emperor penguins will survive. But with “business as usual,” the charismatic penguins made famous for their starring role in the 2005 documentary March of the Penguins are almost certainly doomed.

How climate change is affecting emperor penguins

If climate change continues at its current rate, more than 80% of emperor penguin colonies are expected to become quasi-extinct – the point at which the number of adults may be insufficient to assure persistence of the species – by 2100.

Emperor penguins are especially vulnerable to climate change because, like polar bears in the Arctic, they depend on sea ice for vital life activities like breeding, feeding, and molting. And not just any ice conditions will do for the penguins. Too little sea ice, and the penguins don’t have enough protection from predators or space for molting. But too much sea ice leaves them far from the water’s edge, so they must travel farther – and expend a lot of energy – to find food. So like Goldilocks, the penguins need things to be just right – not too much, and not too little sea ice.

Ice stability is also crucial.

“The reason it’s important to have a thick, stable platform of sea ice is that the chicks that are raised during the breeding season in winter, they have this downy plumage, but they need to acquire waterproof plumage to be able to survive at sea in the cold water,” Jenouvrier says. “So if the sea ice breaks up too early in the season, they will not have acquired this waterproof plumage, and then they will drown and die in the Antarctic water, so it will be a complete breeding failure.”

Three scenarios show potential future of emperor penguins

Jenouvrier’s team used two computer models – a National Center for Atmospheric Research global climate model and a penguin population model – to examine how emperor penguins are affected by sea ice and how sea ice changes affect their mortality and reproduction. For the study, they explored three scenarios: a “best-case” temperature rise of 1.5 degrees Celsius, a 2-degree Celsius temperature increase, and a “business as usual” scenario with a 5- to 6-degree Celsius increase.

With the best-case scenario, they found 19% of emperor penguin colonies would become quasi-extinct by 2100; with the mid-range scenario, nearly one-third of colonies would become quasi-extinct in the same timeframe. These scenarios resulted in a 31% and 44% reduction in penguins, respectively. But their paper notes, “However, population growth rates stabilize in 2060 such that the global population will be only declining at 0.07% under Paris 1.5 and 0.34% under Paris 2, thereby halting the global population decline.”

Jenouvrier says the difference between the Paris Agreement and the “business as usual” scenario is dramatic.

“I think people don’t really understand that with a ‘business as usual’ scenario, it would be another world in terms of climate. Under a ‘business as usual’ scenario, if greenhouse gases continue their current course, the carbon dioxide in the atmosphere is projected to reach 950 ppm and it’s something that’s never been experienced by humans before, and even today, the carbon dioxide in the atmosphere is well above anything we have ever experienced as humans. But today we are at [approximately] 410, and so this ‘business as usual’ scenario is really a different world.”

Picky eaters at more risk than diet ‘generalists’

While the picture is potentially bleak for emperor penguins if the world doesn’t adhere to the 2015 Paris climate agreement goals, not every penguin species will react to climate change the same way. Authors of a recent PNAS study examined how chinstrap and gentoo penguin populations in Antarctica have been affected by human-caused changes, including climate change, historic whaling, and commercial krill harvesting.

While they found chinstrap populations plummeting, gentoos – which are closely related, nest in the same places, and have similar life histories as chinstrap penguins – were actually increasing in number. “Chinstrap penguin populations across the Antarctic Peninsula region decreased by 30 to 53% between 1979 and 2010, while gentoo penguin populations increased six-fold during this same time period,” the study found.

The researchers say that one potential reason for this disparity may be a result of diet adaptation. In order to learn about what the penguins ate in the past, the researchers used an analysis technique to examine feathers from museum specimens so they could consider what the penguins were eating almost a century ago. They examined 40 specimens overall, including five from each of the two species during four different time periods: 1930s, 1960s, 1980s, 2010s.

Their study notes that 100 years ago gentoos “fed almost exclusively on low-trophic level prey, such as krill,” but they adapted to eat other creatures higher up on the food chain, such as fish and squid. However, chinstraps mainly continue to eat just one food: krill. These tiny crustaceans are an important dietary component for many Antarctic animals, but their numbers are in decline as a result of climate change and other factors. Until the mid-1900s, whaling and sealing were thought to lead to decreased competition for krill, resulting in an abundance of it. However, after the International Convention for the Regulation of Whaling was signed, whale and seal populations recovered, leading to more competition for krill. Commercial krill fishing and climate change further reduced krill populations, and the food source was no longer as abundant as it had been.

While chinstrap penguins have short, thick beaks adapted to eat krill, gentoo penguins have beaks more adapted to eat a variety of food items.

The researchers note that their study illustrates how climate change and other factors can affect dietary specialists more than generalists.

The study points to the idea that as the climate changes, specialist species are likely to struggle more than generalists, says study author Michael Polito, assistant professor of oceanography and coastal sciences at Louisiana State University. “As those specialist species do poorly, it could open up the door for other species that are more flexible to really increase in numbers,” Polito says.

What can be done to protect emperor penguins?

While declining penguin populations and human-caused ecosystem fluctuations are concerning in their own right, declining species populations are also an indicator reflecting the health of Antarctica and the world as a whole.

Jenouvrier says she finds it hard to imagine a world without emperor penguins.

“I love seeing the sun rays dance on their plumage and the way they wobble on sea ice,” she says. But she says the possibility of losing the penguins is just one of many consequences of climate change. “It’s not necessarily just about emperor penguins – it’s about all the species on Earth, and it’s about our children,” Jenouvrier says.

But as Jenouvrier’s article notes, people can take action to ensure the survival of these species. “Global climate policy has the capacity to halt future projected declines of emperor penguins in ways that their intrinsic biological properties (i.e. dispersal abilities) do not,” she wrote. In other words, by working to meet the Paris Agreement climate goals, humanity can work to protect penguins and other species.