Why sea ice melting in the Arctic attract more attention?

Question

Why the Arctic is mentioned much more than the Antarctica when it comes to sea ice melting? Is sea ice melting in Antarctica as well? Is there any difference in this phenomena considering that the Antarctica is a continent?

Disclaimer

This answer is only based on my own knowledge, which is trying to my best but sure still limited. I do not hold any responsibility for the credibility of this answer. - LH

Answer

Definition first Sea ice is, as simple as it sounds, ice which was formed from frozen sea water. Glacier is accumulated and compacted snow on mountains or near the poles. It can move slowly under its own pressure. Ice sheets are large masses of continental glacier. Two major ice sheets exist today are in Greenland and Antarctica [1].

The most important difference is that glacier and ice sheet formed from snow thus contain fresh water, while sea ice is frozen salty ocean water. Therefore, the Arctic has only sea ice while all of those above forms of ice exist in the Antarctic.

Sea ice has seasonality. Naturally, sea ice forms in the winter and melts in the summer in both hemispheres. However, because of their geometries, both sea ice area extremes are measured in September [2]. Thus, when we say melting sea ice, we are talking about the decrease of their monitored sea ice in each poles, i.e. the minimum sea ice in the Arctic and the maximum sea ice in the Antarctic.

The Antarctic sea ice is melting as well, but at a slower rate Note that solely based on the seasonality, the sea ice melts every year in the Antarctic is much larger than in the Arctic. The Arctic is almost enclosed with many lands surrounding, thus sea ice cannot escape (except for the direction near Greenland) and keep bumping to each other. On the contrary, surrounding the Antarctic is open ocean, where sea ice can be free to roam and melt when it reaches warm water at lower latitudes. In the winter, sea ice cover around 18 million square kilometres of ocean around the Antarctica but this figure drops to only 3 million square kilometres in the summer. The figures in the Arctic are 15 and 7 million square kilometres, respectively.

However, in terms of sea ice loss by climate change, the Arctic has left its counterpart way behind with 12.8% of sea ice loss per decade (relative to 1981-2010 average) [3]. Since the Arctic is an ocean itself and consists mostly sea ice, rising ocean temperature has a much stronger impact there [4]. On the other hand, the Antarctic has mostly ice sheets over land. Even though its sea ice does melt, its temperature is much lower to be (yet) affected by rising ocean temperature as much as the Arctic. The average temperature in the Antarctic is -60 degree Celcius in the winter and -28.2 in the summer, compared to -40 and 0 degree C in the Arctic.

In general, Antarctic ice is also decreasing, but its glaciers behave more complicatedly. While glaciers in the West Antarctica are melting, its interior and the East’s glaciers are increasing because of heavy snowfall. This actually is another sign of global warming as the moisture increases in warmer climate, leads to more snow. Sientists found that Antarctica’s rate of ice loss has tripled in the last decade [5].

Why does the Arctic attract more attention?

The Arctic has an apparent consequence of sea ice loss. Studies predict that the Artic will be ice free by 2040 [6]. The phenomena of sea ice melting has not yet been very apparent in the Antarctica compared to the Arctic. Furthermore, the land under Antarctic ice makes it hard to measure the exact amount of ice there, while sea ice in the Arctic has quite consistent height of 4 to 5 metres.

Another reason for the attention might be the Arctic’s position. It lies near the busiest maritime trading route in the world, the north Atlantic between the US and the Europe. There is a hot debate on whether the melting sea ice can affect the movement of ocean water, especially the Gulf Stream which bring warm temperature and mild weather to Western Europe and Eastern coast of the US. When the sea ice forms, much of the salt is squeezed out, make the surrounding cold water become saltier, heavier, and sinks, complete the ocean current [7]. With much of sea ice water melt, the water might become less salty, lower density and cannot sink to maintain the Gulf Stream. However, there is still not enough scientific evidence to back up this theory.

Wherever the sea ice is melting in the Arctic or Antarctic, they are consequences of climate change. I’ve just read an article yesterday, stating that we already alter the climate system well beyond its recovery. Even when we stop emit green-house gases immediately, the temperature of the Earth’s atmosphere will keep rising by around 5oC before stabilise and the Arctic might be ice-free by 2040.

References

Image: National Snow and Ice Data Center, University of Colorado, Boulder, Colorado.

[1] https://blogs.ei.columbia.edu/2018/02/05/glaciers-ice-sheets-polar-ice/

[2] Course in Meteorology – Yale University – Lecture 24th: Ice in the Climate System https://www.youtube.com/watch?v=aLj4Lz79d3c&list=PLkUjvobcQS8YGbXinRsEY_2WabKqrPJ4s&index=25&t=0s

[3] https://climate.nasa.gov/vital-signs/arctic-sea-ice/

[4] https://www.dw.com/en/why-is-the-arctic-melting-faster-than-the-antarctic/a-38678700

[5] Shepherd, A., et al., 2018. Mass balance of the Antarctic ice sheet from 1992 to 2017. Nature, 558, pp.219-222.

[6] Holland, M.M., Bitz, C.M. and Tremblay, B., 2006. Future abrupt reductions in the summer Arctic sea ice. Geophysical research letters, 33(23).

[7] https://nsidc.org/cryosphere/seaice/characteristics/difference.html