Last winter, in mid-January, a strong cold snap hit Central and Eastern Europe — the temperature dropped to -30 degrees Celsius, and the drifts rose to rooftops. Similar weather "adventure" in the past two years and experienced people in several cities in the eastern United States, such as Washington, New York and Philadelphia.
The scientists from the Laboratory of Earth and Atmospheric Sciences at Cornell University believe that in the future such events will occur more often. In their opinion, this is due to the sharp melting Arctic sea ice, which would lead to much more severe and rapid climate change than it seems to most laymen.
The melting of Arctic sea ice could cause a domino effect, which dramatically increase the likelihood of severe winters in the northern mid-latitudes.
Global warming increases the melting of sea ice in the summer, opening the dark waters of the ocean in the sunshine. This leads to greater absorption of solar radiation and excessive heating of the ocean in the summer. Surplus heat is released into the atmosphere in the main fall, reducing the gradient of temperature and atmospheric pressure between the Arctic Ocean and the mid-latitudes. This allows the cold polar air to freely penetrate to lower latitudes and cause severe frosts and heavy snowfalls in Europe and the U.S..
The increasing climate variability leads to unpredictable anomalies: in some parts of the Northern Hemisphere winter could be a record warm, while in others — with severe frosts and snowfalls. The latter being with each decade will be more.
In early 2011, the U.S. and Europe hit hard frost, despite the fact that in Greenland and Alaska was unusually warm. This year, at the end of winter in the U.S. and Europe, in contrast, hot, while cold air hovered over Central Europe and Asia. In the Northern Hemisphere winter, extreme weather conditions are usually associated with the negative phase of the Arctic Oscillation — wind patterns that dominate in the polar region. The scientists concluded that the changes in the Arctic may have led to a prolonged stay in a negative mode oscillations.
Charles Greene of Cornell University (USA) pointed out that now the nature of winter in the Northern Hemisphere will change permanently.
When the Arctic Oscillation is in a positive phase, high winds form the so-called polar vortex. Because of him, arctic air masses are blocked near the pole and do not reach the mid-latitudes.
Moreover, thanks to the phenomenon of the atmosphere, jet streams become more direct, and winter was more moderate.
But in recent years, the oscillation is in sharp negative phase, and in 2010 were reported record low temperatures in many regions. The fact that the polar vortex winds weaken, the cold arctic air is mixed with the air masses of the middle latitudes. As a result, jet streams, too, are much weaker and also begins to deviate to the north and south. This leads to the severe cold weather in the U.S. and Europe, but at the same time meandering jet stream can bring to the north over the warm southern air, which is what happened in the U.S. this spring.
Several scientists suggested that a prolonged negative phase may be due to loss of sea ice in the Arctic. For a couple of years, the idea came out of its infancy, having received serious research.
Mechanism similar to the following.
Sea ice is reduced from as long as over the Arctic was a satellite surveillance. It seemed that everyone got used to it, but in 2007 there was a sudden and very sharp decline, from which the ice has not recovered to this day. During all the years (except for one) downward trend was stronger than in previous years (see chart below).
This situation has a significant impact on the local environment. Over the summer, the open ocean absorbs more sunlight than before.
Fall, he returns a portion of the generated heat in the atmosphere, warming the air over the Arctic. This is to some extent blurs the distinction between the Arctic and temperate species, resulting in a probability of formation of the polar vortex is reduced. In short, the lack of ice in the Arctic oscillation introduces a negative phase and increases the chance of a cold winter in the Northern Hemisphere. This, in turn, causes the weakened and become wavy jet stream air to stay longer in the same position.
Tortuosity jets increases the likelihood that the warm southern masses can escape to the north. The March of heat in the U.S. was due precisely to this phenomenon, which coincided with the La Niney in the Pacific: warm air brought to the North, where he was forced to remain unusually long time.
The study is published in the journal Oceanography.
Prepared according to Ars Technica.