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The melting of the Arctic sea ice increases the likelihood of cold snaps in eastern North America, according to several studies. It could also explain the recent heat waves in Europe. A debate on the issue takes place this weekend at the annual meeting of the American Association for the Advancement of Science in Seattle. It is the most important general science meeting in the world.
Over the past decade, more and more studies have shown that winter cold snaps are more frequent in New England and Quebec. “The most common explanation is that the decrease in the area of the Arctic which is covered with ice changes the jet stream responsible for the cold front preventing the very cold air from the pole from descending further south”, explains Thomas Jung , climatologist from the Alfred-Wegener Institute, in Germany, who takes part in the session on this subject on Friday morning in Seattle. “It is paradoxical that this is an effect of global warming. During winter, a larger portion of the Arctic Ocean is in contact with the cold air of the atmosphere and warms it. There are also more rough edges that slow the winds when the water is free, compared to a smooth ice surface. “
Models and observations
Among the dozens of studies on the subject, Jung noted two main trends: modeling is mixed, while studies based on real data tend to confirm the theory of an undulation of the cold Arctic front increasing the risk of “polar” colds in Quebec.
“Modeling is obviously more uncertain, but it must be remembered that we only have 50 years of good data to analyze,” says the German climatologist. So we have to wait for the next generation of climate models, which will be more precise. According to Jung, the size of the individual cells analyzed by current models ranges from 50 to 80 km per side. The new models being tested go down to a size of 16 km for cells. “The chemical and physical equations that make the link between climate and weather are getting better and better,” says Jung. On the other hand, better algorithms or greater computing capacity are required to have smaller, more precise cells. A cell is to a climate model what a pixel is to a photo.
Heat waves in Europe
A corollary of the theory linking the arctic ice and the polar cold further south is that the heat waves which have made thousands of deaths for a decade in Europe are also linked to the melting of the polar ice pack.
“In my opinion, the link is less certain,” says Jung. In summer, Arctic water does not warm the atmosphere of the poles, because they are at the same temperature. I rather believe that the melting of the Arctic pack ice is reducing the strength of the current carrying hot water to Europe, of which the Gulf Stream is a part. This current is responsible for the winds that bring cool water from the ocean to Europe in summer. These winds are less strong, we have more heat waves. “
The new climate models will also be better for taking into account the influence of the ozone layer, which has a significant impact on cloud formation and climate. Exactly, in mid-January in the journal Nature, an American study has estimated that the hole in the ozone layer explains half of the recent melting of the Arctic sea ice. However, the hole in the ozone layer is disappearing as the substances that destroy the ozone layer, used until recently in fridges and air conditioners, disappear from the market after their ban under the Montreal Protocol, in 1987. Does this mean that the rate of melting of the Arctic pack ice will slow down? “It is possible,” said Mr. Jung. But there is a small problem with the concept, because half of the modeling studies do not show that the ozone layer has an impact on the Arctic sea ice. It is encouraging and interesting, but it must be reproduced by other researchers. “
Minimum area, in square kilometers, of the Arctic sea ice in 2017. In 2000, this area was 6.3 million square kilometers.
Source: NASA / La Presse