Antarctic sea ice is increasing. Is the Earth not warming after all?
Klassekampen, 7 Dec 2015
For most people, the Arctic and Antarctic are one and the same thing. It’s cold, and there’s lots of snow and ice. When I recently gave a lecture about the North Pole region, even the organizers did not realize that penguins are common only to the South and polar bears to the North. These two animals, that can only meet each other in a zoo, were standing side by side on the promotion material.
Yet the two polar regions, which couldn’t be further apart, are incredibly different. Antarctica is an immense continent, covered in kilometres of ice, and surrounded by an ocean. The North Pole region, in contrast, has an ocean at its centre with thin floating ice on top, and is surrounded by three different continents. The distribution of ocean and land between the two polar regions is completely different.
These differences are important to understand the consequences of climate change on the ice in the Arctic and Antarctic regions. Although melting ice caps and disappearing sea ice are among the most concrete examples of climate change, many misconceptions persist. This can lead to a wrong narrative.
The melting icecaps are, strangely enough, one of the reasons why there is more ice in the ocean
Take, for example, sea ice. Satellites have shown that the amount of sea ice around the South pole is increasing slightly. Often this is hailed by climate deniers as proof that climate change doesn’t exist: Don't you see? The amount of sea ice is increasing! How can it be true that the earth is warming?
For convenience sake they don’t mention that sea ice in the Arctic declined with millions of square kilometres. Even when the small increase in the Antarctic is included, the balance is clearly negative.
But aren’t there any melting ice caps in the Antarctic? Indeed, but ice caps are not the same as sea ice. One lies on land, the other floats on the ocean. But the two are connected to each other in the Antarctic. The melting Antarctic ice cap is strangely enough one of the reasons why the ice in the adjacent ocean is increasing.
This sounds contradictory but it has to do with the way in which sea ice is formed. Salt water freezes less quickly than fresh water, which everyone who has driven behind a salt truck knows. Sea water is very salt, and therefore doesn’t freeze that easily. But the water from the Antarctic ice caps is fresh. This water is also lighter than salt water and forms a layer on top of the ocean that freezes easily. Due to climate change, the amount of melt water is increasing, which leads to more fresh water on the ocean, and thus more sea ice.
It is true that meltwater is not the only reason why sea ice in the Antarctic is increasing. Changes in weather patterns have also been connected to this trend. But this clearly shows that something as contradictory as increasing sea ice may also be a consequence of climate change.
Contrarily, the effect of climate change on sea ice in the North Pole region is intuitive. The Arctic is warming, and this leads to more sea ice melt. The amount of fresh water in the North Pole region is primarily supplied by rivers, and there hasn’t been a large increase in the outflow towards the ocean. Besides, the disappearance of sea ice strengthens itself: sea ice reflects a lot of sunlight, but open ocean water does not. When sea ice melts and open water forms, it absorbs more sunlight and the water warms up. As a consequence, this extra heat can lead to more melt of sea ice. This effect is one of the reasons why the Arctic is warming two to three times faster than the rest of the world.
This stronger warming also explains why the melt and calving of glaciers from the Greenlandic ice cap has strongly increased since the mid 1990’s. Normally, melt only occurs at its edges, but in the summer of 2012 melt occurred across the entire ice cap. In its entirety, Greenland is the single largest individual source of ice and water to the ocean. But glaciers are also melting at a rapid pace, in the Arctic and beyond.
Our climate is changing, and this change will not be the same everywhere and at every time. Still, there are people who make a lot of noise by pointing at very selective examples without showing the larger picture. For example, the summer of 2013 had more sea ice than the year before because it happened to be a cooler summer. This was heralded by many sceptics as proof that global warming wasn’t happening. If it’s colder somewhere, even for a short while, it is used as proof against global warming.
But just as our summers aren’t the same in every year, does sea ice vary strongly from year to year. The long term trend is much clearer: 35 years of satellite observations clearly show that sea ice in the Arctic is declining by about 14% per decade. Claiming that sea ice is increasing by comparing two years with each other makes about as much sense as claiming that there is a drought when it hasn’t rained for two days.
When all of the relevant factors are considered, only one conclusion is possible: the total amount of sea ice in the polar regions is diminishing, and this cannot be explained without climate change. It is important to know what is the signal and what is the noise.
Processes such as El Niño, and its counterpart La Niña, cause large differences in weather from year to year. Not only in terms of temperature, but also precipitation. Climate change is not the same as a linear warming, and entails much more: droughts and floods, more or less sea ice, cold and warm winters. Apparent contradictions appear in nature just as much as in our daily lives.
This text first appeared in Klassekampen on 7 Dec 2015