There has been a lot of attention on the influence of rapid warming of the Arctic on weather in the Northern Hemisphere mid-latitudes. Much of the work has focused on changes to the Jetstream amplitudes and association of these changes to ice loss in the Arctic.



We know that the Arctic is heating faster than the planet as a whole. Consequently, there is more energy in the Arctic which can be transmitted to the atmosphere. Much of the excess heat is transferred to the atmosphere in the late fall or early winter. This extra energy is connected to what’s called Arctic geopotential height, which has increased during the same times of the year. As a consequence, the Jetstream might weaken in the cold seasons.

But what about summer? Have these changes been detected then too? Well just recently, a paper was published in that answered this question. The authors, from the Potsdam Institute for Climate Impact Research and from the University of Potsdam reported on three measures of atmospheric dynamics (1) zonal winds, (2) eddy kinetic energy, and (3) amplitude of the fast-moving Rossby waves. Rossby waves are very large waves in the upper atmospheric winds. They are important because of their large influence on weather.

Dr. Dim Coumou. Photograph: Potsdam Institute for Climate Impact Research

The authors found that the summer zonal winds have weakened. The reason for the weakening is that since the Arctic is warming faster than the rest of the planet, the temperature difference between the Arctic and the lower latitudes is getting smaller. It is this temperature difference which maintains the wind speeds. The authors also found that eddy kinetic energy is decreasing.

So what does all this mean? Well two things. First, it means that there are either fewer or less intense summer storms or a combination of both. But secondly, it means that weather patterns can get “stuck”. Storms are excellent at breaking up persistent weather patterns, and bringing cool and moist air from ocean regions to land zones. With fewer storms, “warm weather conditions endure, resulting in buildup of heat and drought.”

The authors looked to the future to inquire about how things would continue to change. They find that continued global warming will increase the risk of heat waves. We all know that the warming temperature will make heat waves more likely. But added to this, “stickiness” of weather patterns will play a big role as well.

Whether it is the heat wave in Europe of 2003, the Russian heat wave of 2010, the heat waves in the USA in 2011 or 2012, or last year’s (and still continuing heat in California), these events have economic and human consequences. It is crucial to understand how our current climate works if we have any hope in predicting what will happen in the future. This study makes a great contribution to putting the puzzle of the Earth’s climate together.



I asked colleague Dr. Stefan Rahmstorf about this work and he said,