Over the past 50 years, the west coast of the Antarctic Peninsula has been among the most rapidly-warming parts of the planet. The east coast of the Peninsula has also warmed, though less rapidly. Significant warming has also been observed in the Southern Ocean, with upper ocean temperatures to the west of the Antarctic Peninsula having increased by over 1°C since 1955. Associated with this warming trend, sea ice declines in the Antarctic Peninsula region have already been observed (IUCN 2009).
Changes in seasonal sea ice are potentially a significant threat to breeding Emperor Penguins. Although it is possible that a reduction in sea ice could actually benefit Emperor Penguins by reducing the distance adults must travel to feed during the breeding season, there are important negative effects that should be considered. Pack ice extent reaches its minimum in late summer. At this time, however, ice is still essential as a platform for crèched chicks before they fledge, as it is later for adults to moult successfully. Growing chicks and moulting adults are unable to survive in the ocean without their waterproof feathers. Early ice break-up in warm years has caused chicks to be swept into the ocean and drown (IUCN 2009).
Should global temperatures increase by 2°C, scientists estimate that colonies to the north of 70°S would probably become unviable. This would impact 40 percent of all colonies, and nearly 40 percent of the total breeding population of Emperor Penguins (IUCN 2009).
In 2001, a large iceberg collided with the Ross Sea ice shelf in the vicinity of a well-established Emperor Penguin breeding colony. The sea ice supporting a considerable proportion of the colony was broken. In addition to the direct impacts of the collision, the colony was affected for several years afterwards by the continued presence of the iceberg. Chick production was markedly reduced and remained lower than usual for some years (IUCN 2009). With increases in temperature and thinning of the sea ice, such events are likely to occur more frequently.
Reduced food availability is another potentially serious consequence of a warming climate. Antarctic krill are small, extremely abundant shrimplike invertebrates that form the basis of much of the Antarctic food web. Krill feed on phytoplankton in the open ocean or on the underside of sea ice. Projected declines in sea ice extent are likely to reduce the number of krill in the Southern Ocean, which would, in turn, have profound effects on the Antarctic food web. In addition to its direct effects on Emperor Penguins, krill availability is likely to impact the abundance of penguin prey species such as fishes and squid, which also feed on krill (IUCN 2009).
Emperor Penguin colonies exist at the edge of the Antarctic continent, so there is little potential for colonies to move southward. However, two Emperor Penguin colonies are known to occur on land rather than on ice, and these have remained stable over the last 20 years. This suggests that other colonies might potentially shift to land as sea ice decreases, though this would depend on finding land areas with suitable access to food resources, a feature that is likely key to determining the location of Emperor Penguin colonies (IUCN 2009).
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