A decline in the population of emperor penguins appears likely this century as climate change reduces the extent of Antarctic sea ice, shows a recently published US study.

The research, led by the Woods Hole Oceanographic Institution (WHOI) and published this week in Global Change Biology, focuses on a much-observed colony of emperor penguins in Terre Adelie, Antarctica.

Employing a set of sophisticated computer simulations of climate and a statistical model of penguin demographics, the authors conclude that the number of breeding pairs may fall by about 80 percent by 2100.

Building on previous work, the team examines how the sea ice may vary at key times during the year, such as the seasons of egg laying, incubation and chick-rearing, and how the sea ice concentrations may influence the males and females.

The authors stress that their projections contain large uncertainties, because of the difficulties in projecting both climate change and the response of penguins.

However, almost all of their computer simulations point to a significant decline in the colony at Terre Adelie, a coastal region of Antarctica where French scientists have conducted penguin observations for more than 50 years.

"Our best projections show roughly 500 to 600 breeding pairs remaining by the year 2100," says lead author Stephanie Jenouvrier, a WHOI biologist. "Today, the population size is around 3,000 breeding pairs."

Another penguin population, the Dion Islets penguin colony close to the West Antarctic Peninsula, has disappeared, possibly because of a decline in Antarctic sea ice, according to the biologist.

The nearly 1.2-meter-tall emperors are the largest species of penguin. They are vulnerable to changes in sea ice, where they breed and raise their young almost exclusively.

If that ice breaks up and disappears early in the breeding season, massive breeding failure may occur. Disappearing sea ice may also affect the penguins' food sources.