We knew that the Gulf Stream, the ocean current that plays a major role in the world's climate, was going off course. Scientists now agree that another current, this time in the air, at an altitude of about 15 kilometres, the Jet Stream, was also in the process of being disrupted because of climate change. It would be responsible for the increasingly intense and long-lasting heat waves we are experiencing.
Dfirst year post We recently explained how scientists became convinced that the Gulf Stream, the ocean current that regulates global temperatures, especially in the northern hemisphere, was being disrupted. Its weakening could have extremely serious consequences for the climate of the world in general and our regions in particular.
A long river not always quiet
Climate scientists are now concerned about another current, the air current, which influences the weather on a daily basis by interfering with the cold and warm air fronts that shape depressions or anticyclones. This air current is located in our atmosphere between the troposphere, where the temperature decreases with altitude, and the stratosphere, where the temperature increases with altitude. It takes the form of a river of air, several thousand kilometres long but only a few hundred kilometres wide and only a few kilometres thick. This current is located at an altitude of about fifteen kilometres and is called Jet Stream because of the speed of its current. Winds flowing from west to east can reach speeds of up to 360 km/hr.
One of the characteristics of the Jet Stream is its meandering shape. Like a long river that is anything but quiet, it surrounds the planet, but the position of its ripples, as well as its speed, can vary significantly. This current forms a barrier between warm air masses coming from the tropics and cold masses coming from the Arctic. Temperature differences between these two air masses accelerate or slow the speed of the Jet Stream.
When the temperature difference decreases, the current slows down and forms north-south ripples which can lead to blockage situations. When an area is under the influence of a southern curve of the Jet Stream, the weather will freeze in high temperatures for an unusually long period of time. This is the situation France found itself in in 2003 with a heat wave that lasted about three weeks and caused the premature death of 15,000 people.
Blocking situation
A study led by climate scientist Michael E. Mann of the University of Pennsylvania, USA, was published in the journal Scientific Reports on March 27th. This research shows that temperatures are warming twice as fast in the Arctic as in the tropics. The consequence is mechanical: the differences in temperature between the two zones on either side of the Jet Stream are reduced, leading to a weakening of the current and a situation where its ripples are blocked.
This phenomenon, caused by anthropogenic warming of the global climate, could lead, according to scientists, to an increase in the number and duration of heat waves around the world, particularly in our regions.
Other climatologists at the University of Hawaii have been working on heat waves around the world. They have compiled statistics recorded since 1980 from nearly 2000 locations around the world. In the debriefing of their research, they established the threshold for heat wave mortality. According to them, if nothing is done to stem the rate of global warming, 74 % of humanity will face deadly heat waves.
In France, the African summer
As regards France, the magazine Science published the results of the Euro-Cordex model. This model estimates that heat waves will increase in our country and that by the end of the century, they will be 10°C warmer than today! To make matters worse, these heat waves will last from 10 to 60 days depending on the region, making our summer seasons resemble the worst African summers.
The heat wave that France is going through at the moment is only a foretaste of what is likely to become an unbearable habit.
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