Vendée Globe

Around Antarctica, there are said to be an increasing number of icebergs. People say they are moving further and further north and global warming is widely considered to be the cause.
Three accusations that are so commonly made that they have become widely accepted as fact, but at the moment, nothing can confirm the accuracy of these statements. We put this question to David Salas, a researcher at the French Weather Research Centre (CNRM), who is a specialist in the Antarctic.
 

Warming: little change in the Antarctic
Firstly, with regard to global warming, the Antarctic is in many ways the exception to the rule, although we must add a word of caution, as it is the least well-known continent and has not been fully explored. «Explorers and scientists only really discovered it relatively recently, so we don't have the benefit of hindsight,» David Salas warned from the outset. «The data at our disposal dates back to the last International Polar year (1957-58). What we can say about the last fifty years is that we have the impression that the climate patterns in this region are still insulated from what is going on in the rest of the world. Indeed, if the Western Antarctic, in particular the Antarctic Peninsula (the part that points up towards South America, editor), has warmed slightly, we can see that the eastern side, which represents two thirds of the continent, has grown colder. It should be said that we are talking here about a large inert mass (14 million square km), covered to a depth of 2-3000 m by ice, and which stores 90% of the world's fresh water. If everything melted, the oceans would rise 60m! The Antarctic will certainly not escape warming. Looking ahead to 2100, the climate models show a rise in temperature by three degrees. However, with averages currently around -50 to -60° in the central area, it will continue to be very cold. One amazing effect of warming is an intensification of the hydrological cycles: this continent will experience heavier rainfall and will see more snow and ice. Thus, the Antarctic will contribute to a reduction in the levels of the seas by 1 mm, a negative effect that is more than compensated by the melting of the Arctic ice and the rise in sea levels.»

Icebergs: down to chance
As far as the ice is concerned, we can say that the large flat icebergs commonly found in this region come from the Polar Ice Cap. We are talking about bits of the ice cap that have broken off and can sometimes drift in the ocean taking advantage of the fragile nature of the Ross and Weddell ice banks in particular. But according to Davis Salas, this split from the ice is down to chance: «While we can observe many of them at the moment, we can imagine not seeing any again for the next ten years!» The large number of pieces of ice spotted in the Vendée Globe with the help of CLS Argos are basically icebergs created a long time ago, perhaps back at the turn of the Century, when many giant pieces of ice broke away.

Size and sea temperature, determining elements
The researcher went on to explain that for icebergs to drift northwards in the Antarctic currents, they need to be very big. In 2006, it was thought that the ice to the south of New Zealand came originally from an iceberg measuring 8500 km²! The bigger they are, the longer they take to melt and the further they travel in the southern seas. David Salas points out a fact that seems quite logical about the long term: «Everywhere is going to get warmer, and the same goes for the temperature of the ocean. If an iceberg broke away in 2100, it would take much less time to melt than is the case today. Theoretically, it is likely not to travel as far.» So the big question is will the icebergs in ninety years be much bigger than today. «That is impossible for us to say for now.»

So in conclusion, the fact that there has been a lot of ice spotted in the last few years by sailors racing around the world is maybe simply an illustration of an episode lasting ten years or so, rather than the beginning of a phenomenon, where we would continue to see icebergs in increasing numbers over time. It would therefore appear to be incorrect to assert that this is the direct consequence of global warming.

Camille El Beze
 

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