Antarctic Ice and Climate Change

The study of Antarctic ice is important in determining how the world’s climate is changing, how climate change affects Antarctica, and how ice contributes to climate change. Antarctic ice can tell us about past climate and thus show climate change through the study of ice cores. Observations of changes in ice and how if affects other parts of the Antarctic ecosystem can also be used to determine current climate change and to predict the effects of current climate change. There is already evidence of sea ice melting affecting the krill and penguin populations. The ice itself can also be an element that changes climate, thus one of the reasons the study of ice and climate change is important in understanding global climate change. Thus climate change caused by an increase in greenhouse gases has the potential to cause changes in the Antarctic ice that can lead to further global climate change.

There has been an overall warming trend in the Antarctic and Southern Ocean region over the past half a century.¹ The annual average temperature for the Antarctic Peninsula has warmed by 2.5 degrees Celsius over the past fifty years.² The average temperature for the rest of the region has increased on average one degree Celsius.³ The surface waters of the Southern Ocean have also warmed and become less saline.⁴ During this period there has also been an increase in precipitation in the region. This observed warming in climate change has an affect on the ice on and around Antarctica.

In Antarctica there has been increase in the calving of bergs a possible sign that if the current warming trend continues a rapid break up of the continent’s largest ice shelves, such as the Ross, will occur.⁵ It is possible that the whole West Antarctic Ice Sheet will melt due to global warming. However, it is more likely, at least in the short term, that global warming will cause an increase in precipitation over the Antarctic continent resulting in most of the Antarctic ice sheets thickening.⁶ There is little supporting evidence for a rapid melting of the West Antarctic Ice Sheet even in the long term. However, even the slow melting of these freshwater sources will slow down the ocean’s thermohaline circulation,⁷ which helps keep Europe warm.⁸

In the Antarctic Peninsula region there has been extensive retreat and collapse of ice shelves.⁹ This region has also experienced a steady decrease in the extent of spring and winter ice.¹⁰ The frequency of winters with extensive ice cover has decreased over the past five decades.¹¹ This decrease in sea ice negatively affects krill and the animals that depend on krill for their survival in the Antarctic region.

In one area Antarctic krill numbers have dropped about 80% since the 1970s.¹² Krill populations are declining due to a reduced amount of sea ice and the associated ice algae that krill feed on. The reduced sea ice causes krill to spawn in March instead of between December and February resulting in poor recruitment.¹³ The same conditions that create poor recruitment in krill are favorable for salps. Salp populations are increasing as they can take advantage of the increase in cryptophytes that occurs when sea ice extent is minimal, while krill cannot.¹⁴ The decline in krill is linked with the decline in Adélie penguins, crabeater seals, and other krill predators that rely on krill as a large part of their diet. The decline in krill also causes a decline in the Southern Ocean’s sequestering of carbon dioxide, as the krill are responsible for bringing large amounts of carbon dioxide from the ocean’s surface to the ocean’s interior, where the carbon dioxide is sequestered¹⁵

Adélie penguins live and breed all around the Antarctic continent and Peninsula, as well as on a few sub-Antarctic Islands. The recent decline of Adélie penguin populations, which is up to 50% in some colonies on the Peninsula, is attributed to the negative effects of the current trend of warming. In the Antarctic Peninsula region the winter and spring sea ice maximum has been decreasing as a result of a warming trend in the region. There is a greater availability of krill in the years when ice cover is more extensive.¹⁶ As a result of the loss of the sea ice habitat and the krill abundance associated with it, Adélie Penguins in the Antarctic Peninsula and nearby sub-Antarctic island region are in danger of a continuing decline in population size, especially in areas where they must compete with Chinstrap penguins for the limited supply of krill.

Chinstrap penguins are found on the Antarctic Peninsula and on many sub-Antarctic Islands. Warming in Antarctic appears to produce more favorable conditions for Chinstrap penguins than for Adélie penguins. Where these two species breed side by side, the Chinstraps are able to exclude the Adélies from the potential inshore foraging areas during years with low krill availability resulting in lower reproductive success for Adélies than for Chinstraps.¹⁷ Low krill availability does lower Chinstraps reproductive success, but it does not appear to pose a real threat at least in the short term. The Gentoo penguins with a similar range as the Chinstraps have also been less affected than the Adélies by the low krill availability.

Emperor penguins live on the Antarctic continent year round breeding on the disappearing sea ice. Adult survival is strongly positively correlated with years of extensive sea-ice and strongly negatively correlated with years of warm sea surface temperatures.¹⁸ Stable sea ice is necessary for Emperor penguins during the molting period because during this period they cannot survive for long in the water.

Not only does climate change affect Antarctica’s ecosystem, but also Antarctica’s ecosystem with its ice can further affect global climate change. The contribution to sea level rise from ice melting in Antarctica is uncertain at present.¹⁹ However, the melting of the West Antarctic Ice Sheet has the potential to cause sea level to rise up to 18 feet. The melting of Antarctic Peninsula ice shelves has little impact on sea level rise, as they are floating.²⁰ The West Antarctic Ice Sheet is not expected to melt any time soon, as it is actually expected to grow in the short term due to an increase in precipitation caused by climate change. It is possible though that it will melt if the current trend of global warming continues in the long term. If and when it does melt it is likely to be a slow process taking several centuries to fully melt, thus it contribution to sea level rise will be a small amount a year, but overall resulting in submerging whole island states and the altering of coastlines. While the effect of Antarctic ice melt is likely to be a slow rise in global sea level, the cool fresh water entering the ocean from the ice sheets may further affect global climate, especially that of Europe, by slowing down the oceans’s thermohaline circulation.

Substantial warming and increases in precipitation are projected for the Antarctic region over the 21st century by almost all climate change model.²¹ The average increase of temperature for the region is predicted to be 0.5 degrees Celsius.²² Precipitation is expected to increase 20 percent by the end of the 21st century.²³ The projected climate change is also expected to cause the Southern Ocean to uptake less carbon dioxide thus allowing a faster increase in greenhouse gases our atmosphere.²⁴ The loss of ice and its high albedo in the region will cause further warming, as less solar radiation is reflected.²⁵

¹IPCC, Climate Change 2001: Impacts, Adaptation, and Vulnerability, (Cambridge, UK: Cambridge University Press, 2001)