In many places in the northern hemisphere heatwaves have recently been raging. In the past, heatwaves have killed dozens of victims in South Korea and Japan. They have also caused severe droughts, which are a perfect breeding ground for the very large fires that once broke out in California and Australia.
Découvrir notre dernier podcast
These events bear witness to one thing, heatwaves and droughts are lengthening their duration since the weather has remained hot, dry, and cloudless without precipitation for too long. This phenomenon could well be related to what is happening at the North Pole. The warming and melting of the Arctic ice could indeed be causing a weakening of certain atmospheric currents of air which are essential for the climate, known as the ‘jet-stream.’
As air currents stagnate, heat waves continue
This current is produced by a meeting between the cold air from the poles and that from the warmer zones closer to the equator. In our hemisphere, the warm air coming from the south moves towards the North Pole and is at the same time moved towards the east by the rotation of the earth. These different movements create a kind of curving current. The current moves continuously across the hemisphere, at an altitude of between 26,000 and 40,000 feet, with winds usually reaching 185 mph.
This summer, however, this current, among others, has been more focused on Europe, with less intensity than usual. The strength of the jet-stream depends on the temperature difference between the air masses of the hot and cold regions. The bigger the difference, the faster and stronger the current is. The hot air masses usually cool, but this is becoming more difficult due to recent global warming trends. The North Pole side of things must be looked at instead.
The Arctic is heating up too quickly
According to Jennifer Francis, a New Jersey-based climatologist and Rutgers University professor in New Jersey, when the cold air from the Arctic warms up, the jet stream slows down, almost to the point of stopping completely. It then cements the climate into a specific trend for a long period of time. Instead of swirling around the globe, the winds move back and forth around the same position. The air masses are thus stuck in one place.
According to a 2004 study, the warming of the Arctic is occurring twice as quickly as that of average global warming, and human activities are largely to blame for this. This year's events are no exception, according to Jennifer Francis. ‘Is it due to global warming? I think we can answer yes with confidence.’
Influence of melting ice on the jet-stream still debated
Although the warming of the Arctic is rather well established, the reasons that have led to such a warming of the air are still debated. According to Jennifer Francis, one of the major elements is the melting of the ice in the Arctic. Sea ice levels recede from year to year, and their cooling action on the air would explain the lack of strength of the jet stream. But this hypothesis is not unanimous.
For Gavin Schimdt, a NASA scientist working at the Goddard Institute for Space Studies, the link is far from certain. He explained to the New Scientist:
The direct link between extreme temperatures and jet stream fluctuation is valid, the discussion is about establishing a causal link between the withdrawal of the ice pack and these events.
According to Gavin Schmidt, the jet stream is highly variable when looked at over periods spanning several decades. The correlation with the decline in ice cover could thus only be coincidental.
Whatever the reason for this warming, the cold air masses coming from the Arctic heat up faster than the hot air masses coming from the equator. If this situation does not change, the extreme weather events of this summer could begin to occur more and more frequently.
