The Emperor Penguin (Aptenodytes forsteri) is uniquely adapted to breed in the Antarctic winter - eggs are laid and chicks reared mainly on stable sea-ice. Climate change is bringing increasing pressure to bear on the Antarctic. It is impacting upon the physical environment, on which species like the Emperor Penguin largely depends (1, 2). Emperor Penguin adult survival is linked to the extent and stability of sea-ice in winter (3, 4), and stable ice conditions are required for the moult (5). Climate change is altering the extent and composition of sea-ice (1, 2, 6).Sea-ice extent is influenced by the interconnected atmosphere-ice-ocean system of the Southern Ocean, which is the most complex, hardest to study, and least understood of Earth’s biomes (1). Overall, sea-ice area has been expanding slightly in Antarctica since the 1970s, but with large regional variations in both increases and declines (2). Sea-ice expansion may be due at least partly to climate change melting ice shelves, which in turn results in a cool, fresh surface layer on the sea which delays sea-ice from melting (6).
Because Emperor Penguins are mostly dependent on stable sea-ice to breed, an increase in regional warming due to climate change may negatively impact their population by changing the extent, formation and persistence of ice (5). In 2001, research showed that an Emperor Penguin colony at Terre Adélie was particularly vulnerable to climate change because of the effect of the reduction of sea-ice extent (3). Further modelling of the Terre Adélie population estimated that the probability of extinction of the Emperor Penguins in the area could be at least 36% (7), and up to 81% by the year 2100 (8). The research also emphasized that an increased frequency of warm events, with subsequent decrease in sea-ice extent, would reduce Emperor Penguin population viability there. If the Earth warms more than 2°C above preindustrial levels, a likely scenario(9), it has been estimated that approximately 40% of the entire Emperor Penguin breeding population may decrease or disappear (10). In 2011, the loss of a small Emperor Penguin colony (~150 breeding pairs) was recorded and attributed to regional climate warming (11).
Many factors may influence the ongoing viability of Emperor Penguin populations, and it has been shown that colonies in different areas can have contrasting population changes (12), which is also the case for other penguin species (12).The concern that climate change may accelerate declines in Emperor Penguin populations has been raised previously (3, 7, 8, 10-12, ATCM XXX/IP5, ATCM XXXV/IP45, ATCM XXXIII/WP16). Current evidence suggests that understanding of the influence of climate change on Emperor Penguin populations is not yet comprehensive (3, 7, 8, 10-13). However, population declines have been demonstrated (3, 14) and are projected to become more extensive (7, 8, 10).
The discovery of new colonies of Emperor Penguins in 2012 has meant an upward revision of total population size estimates from ~155 000 to ~238 000 breeding pairs (15). Also, satellite and aerial-surveys have, for the first time, documented Emperor Penguins breeding on ice-shelves, as opposed to sea-ice. These findings suggest that the species may have a larger population size than formerly thought, and may be capable of adapting their behaviour in the face of changes to their primary breeding habitat(16). At present, following the Intergovernmental Panel on Climate Change (IPCC) guidance on descriptions of uncertainty (17), the available evidence can be considered limited to medium, but with high agreement. Thus, negative climate change-related impacts on the Emperor Penguin can be considered likely.