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CLIMATE/ Cold winds from the Arctic, but this is not “The Day After Tomorrow”

STEFANO ALIANI explains the wind phenomena over the Arctic that cause cold air to move down to lower latitudes, even during a period of global warming.

(Infophoto) (Infophoto)

Particularly abundant snowfalls and exceptional minimum temperatures were recorded in various areas of North America, Europe and Asia during the winter of 2009-2010. Now the cold wave has hit Europe again, causing major disruptions in Italy and in areas not usually affected by heavy snowfall.

Since the measured temperature in the Northern Hemisphere has been confirmed to be on a trend toward global warming without any reversal of this pattern, public perception is inevitably influenced by these cold events and skepticism in increasing toward global climate change.

It would seem logical to say that if the planet is warming, we should expect a decrease in snow and cold events, but in recent years it has not been so, at least in Europe and North America. In short, the scenario is controversial, and this is not conducive to reaching shared awareness that the climate is changing, an essential step in initiating the process of the mitigation of anthropogenic impacts.

Studying the climate of the Arctic seems disconnected from our everyday life and terribly far away, but it is essential to understanding and predicting the phenomena that we are facing these days.

The Arctic Oscillation (AO) index describes the pattern of intensity of a semi-permanent center of low atmospheric pressure above the North Pole, around which winds turn and form a vortex. When the AO is positive, the vortex is strong, and the winds are more tightly compressed around the North Pole, preventing cold air from leaving the high latitudes. When the index is negative, the vortex is weak and cold air is able to extend further south. From the '80s to today, the AO index in winter has generally been positive, producing a relatively mild climate. Occasionally, the vortex is reversed, cooling Europe and North America.

The AO and temperature are manifestations of one another, but the fact that they are related does not imply causality. This is because the AO is not a mechanism that brings heat or cold in itself, but is a symptom of developments in the climate. It has been described as a physical and dynamic structure that moves around the Pole and occasionally creates special weather conditions, but that is actually not true.