Scientists from the Potsdam Institute for Climate Impact Research have conducted a study which showed that rapidly meting Arctic caps are responsible not just for milder winters (due to a weaker Jetstream), but for summer heat waves as well.
So far, it had been established that, because the Arctic is heating faster than the rest of the Earth, it releases more energy into the atmosphere. The excess of heat is released in the air mostly near the end of each year (late autumn or early winter), when the Arctic geopotential height is greater. This has a weakening impact on the Jetstream. The new paper, published in Science by the Potsdam team of climatologists, presents the results of three types of measurements: zonal winds (winds that blow at certain latitudes, like jet streams), eddy kinetic energy (measuring the turbulence in air masses) and the amplitude of Rossby waves (large westward waves in the upper atmosphere caused by the Coriolis force in rotating fluids).
The conclusions were the following: first of all, summer zonal winds have weakened because what normally triggers them is the temperature difference between the Arctic and the mid-latitudes, and since the Arctic temperature is decreasing, the difference from mid-latitude temperatures is smaller too, so that the air stops flowing from one zone to the other. Secondly, eddy kinetic energy is also smaller than it used to be. These changes imply that there are fewer conditions for summer storms, but this also means that there will be smaller chances of strong summer winds bringing colder and moister air from the areas above oceans to the ones above the land. The consequence is that summer heat waves are bound to grow in intensity. If global warming goes on at the same pace, heat waves and droughts will become more and frequent.
The prognosis isn’t an optimistic one, according to study co-author Jascha Lehmann, who warned that the high temperatures experienced so far “might be just a beginning”. Because the variety of atmospheric dynamics has been decreasing over the last decade, weather trends tend to be more persistent, and this includes high-temperature trends during the hot season.
The scientific importance of this study resides not just in its forecast value, but in the fact that it opens the door to understanding the dynamics of global warming, which does not simply mean that the Earth is getting warmer, but that the working mechanism of its atmosphere is undergoing a systematic change and could be reconfigured as a whole. Global warming affects not just temperatures, but also winds and atmospheric pressure and atmospheric humidity, which is why its impact is feared so much.
image source: Woods Hole Oceanographic Institution