The Antarctic and Arctic regions are polar opposites in more ways than one. These two regions have differences in the volume of ice, their climate, their seasonality, and much more. One important feature which separates the Arctic and Antarctic regions is their sea ice, and in particular how it changes over the year and its extent. This page looks at what sea ice is, and why it is important. It then explores the differences in the Arctic and Antarctic regions, how they have changed over time and what may happen in the future.
What is sea ice, and why is it important?
Sea ice is frozen sea water which floats on the ocean’s surface surrounding the Arctic and Antarctic regions. Sea ice interacts with a range of global systems, such as the global ecosystem. For example, polar wildlife such as krill in the ocean, to the penguins on land. These are all dependent on sea ice for breeding, feeding and shelter.
Sea ice also interacts with the climate system. It helps with the heat exchange between the atmosphere and the polar regions . The white surface colour of the sea ice means it has a high reflective index causing most of the suns incoming solar radiation to reflected back out to space. This keeps the polar regions cool. It also interacts with the ocean currents which help distribute heat around the globe.
Arctic Sea Ice
The sea ice extent in the Arctic region covers the highest latitudes. It surrounds Greenland, the northernmost coast of Canada, Russia, and the High Arctic during the winter months. Sea ice in the Arctic region changes seasonally. During the winter, as temperatures decrease the sea water freezes and eventually reaches its maximum extent in March. It then melts during the summer, and reaches its minimum extent in September. In September 2020, Arctic sea ice reached a maximum extent of 3.2 million km2 which was over 3 million km2 below the long-term average [1,3].
Long-term trends in sea ice has shown clear declines in most areas of the Arctic, with the last four decades being the most significant [2,4]. This decline is mainly attributed to the continually increasing air temperatures from anthropogenic activity. However, there has also been links to natural variability in atmospheric circulatory patterns across the North Atlantic region .
Antarctic Sea Ice
Antarctica is surrounded completely by the ocean. Because of this, the sea ice forming in the winter months is not constrained by surrounding landmasses, unlike the Arctic. This allows the sea ice to spread over a much larger area.
Much of the sea ice which has built up in the winter months (March to September) is melted in the summer, leaving only isolated areas in the Weddell and Ross Seas. The maximum sea ice extent in the Antarctic region peaks in September to October reaching areas greater than 18 million km2 .
Unlike the Arctic’s long-term decline in sea ice extent, the Antarctic region over time has shown slight increases. Since the 1970s, satellites have shown an approximate 1% per decade increase in extent until 2014 . Increases in sea ice extent has been attributed to changes in wind patterns, and from localised cooling of sea surface temperatures from direct glacier melt and ice shelf collapse .
However, Since 2014 this increasing trend has turned. We can now observe a gradual decrease in its extent. It is unclear as to whether this decrease is as a result of climate change, or from natural climate variability, however scientists are continuing to monitor its change .
A more detailed explanation on Antarctic sea ice can be found here.
Changes in Sea Ice Over Time
Click on the figure below to be taken to the Sea Ice Aware infographic, produced by ESRI. This application allows you to explore both the Arctic and Antarctic Sea ice since the 1970s. You can see the differences in the annual cycle of sea ice in these two different polar regions, how much it has changed over time, and the minimum and maximum extent each year.
Future of Global Sea Ice
Anthropogenic climate change is already having effects on global sea ice. The IPCC Special Report on the Oceans and Cryosphere  have shown how these trends are likely going to continue into the future. The impact of climate change on the Arctic is more linear than the Antarctic. In the Arctic, there is a clear relationship between the increasing temperatures and decreasing sea ice. However, the impact on Antarctic sea ice is slightly more complex due to lots of interacting systems. However, modelling attempts still predict a gradual decline in sea with future climate change .
The decline in sea ice will continue to have notable implications for marine wildlife. The IPCC showed how in the Arctic, predictions for many marine mammals and birds are going to likely decline in the future, threatening populations. But there are also concerns that populations of some sub-Arctic fish species will continue to increase, adding more stress on an already delicate ecosystem [6,7]
In Antarctica, there is also a clear threat to species which depend on sea ice. Most significantly is the effect that the decline in sea ice will have on krill. Krill is a key species for the Antarctic food chain, and without them, knock on effects will be seen in other marine and terrestrial wildlife.
To explore Antarctic sea ice more, check out our StoryMap Collection below.
1. Hofsteenge, M.G., Graversen, R.G., Dydsaa, J.H., and Rey, Z. (2022) The impact of atmospheric Rossby waves and cyclones on the Arctic sea ice variability. Climate Dynamics.
2. Cai, Q., Wang, J., Beletsky, D., Overland, J., Ikeda, M., and Wan, L. (2021). Accelerated decline of summer Arctic sea ice during 1850-2017 and the amplified Arctic warming during recent decades. Environmental Research Letters. 16, 034015
3. Strove, J., and Not, D. (2018) Changing state of Arctic sea ice across all seasons. Environmental Research Letters. 13. 103001
4. NASA Earth Observatory (n.d.a) World of Change: Antarctic Sea Ice. Available at https://earthobservatory.nasa.gov/world-of-change/sea-ice-antarctic [accessed 17th January 2022].
5. Bintanja, R., G.J. van Oldenborgh, S.S. Drijfhout, B. Wouters, and C.A. Katsman, 2013. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion. Nature Geosci.
6. IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.
7. IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. In Press.