When the retreating Arctic sea ice fuels snowstorms in Europe

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Between February and March 2018, Europe suffered a winter episode marked by heavy snowfall. Some countries of the north were paralyzed while the snowflakes invited themselves to the south of the old continent. However, recent work shows that this event was greatly accentuated by the retreat of the Arctic sea ice.

The meteorological landscape of our latitudes is distinguished by the significant thermal variations that occur from week, month or year to year. Paced by the movements of the atmosphere, tropical and polar air masses thus indulge in a continual alternation, but complex because irregular. As such, the way in which the weather patterns succeed one another on the scale of a country like France appears to be akin to total chaos.

Despite the erratic and particularly complex dimension of atmospheric circulation that affects our territories, they are not immune to global warming of the planet. Indeed, since the atmospheric fluid is gradually heated, its movements stir progressively warmer air. Consequently, southern flows more easily bring extreme heat while polar flows more difficultly lead to excess cold.

Simulation of temperature anomalies in 2012 and 2090 according to a pessimistic climate scenario. The deviations are from the 1980-2010 normal at a daily resolution (here for March 16). Note that even at the end of the century, the cold anomalies have not completely disappeared. Credits: National Center for Atmospheric Research.

Increased snow potential in Europe during winter

Another consequence associated with brewing an atmosphere that is already around 1 ° C warmer is humidity. Since the water content of the air depends on its temperature, anything that involves precipitation – whether it is rain or snow – will also be affected. And sometimes in a rather unintuitive way, as evidenced by a new study published in the journal Geoscience of nature at the beginning of April.

The researchers showed that the combination of a warmer atmosphere and a deficit of pack ice in the Barents Sea contributed to the heavy snowfall that hit Europe in February and March 2018. While circulating above arctic seas with very little ice, the air was able to charge more efficiently with water vapor. Then, propelled south by a vigorous north to northeast flow, this moisture fed heavy snowfall across the European continent.

“Climate change does not always manifest itself in the most obvious way” reports Alun Hubbard, co-author of the paper. “It’s easy to extrapolate models to show that winters are getting warmer and to predict a virtually snow-free future in Europe, but our most recent study shows that’s too simplistic. We should beware of overly general statements * on the impacts of climate change ”.

snow cloud europe
Satellite image from March 15, 2018. Note the airflow passing over the Barents Sea and enriching in moisture (cloud bands). We are talking about streets of clouds. Credits: NASA.

An origin revealed by the isotopes of water

These innovative results result from the isotopic analysis of precipitated water in northern Europe. Indeed, combined with satellite data, the geochemical method made it possible to trace the origin of the humidity. It reveals in particular that nearly 90% came from open water surfaces in the Barents Sea. More precisely, the equivalent of almost 10 millimeters of water per day. The data indicates that around 140 billion tonnes of water evaporated from the unusually warm sea during the event.

“What we are seeing is that sea ice is like a cover over the ocean”, explains Hannah Bailey, lead author of the study. “And with its long-term reduction in the Arctic, we are seeing increasing amounts of moisture entering the atmosphere in winter, which has a direct impact on our weather conditions further south, causing extremely heavy snowfall. . It may sound counterintuitive, but nature is complex and what happens in the Arctic does not stay in the Arctic ”.

Finally, the authors show that between 1979 and 2020, the amount of evaporated water – and therefore potential snowfall – in northern Scandinavia increased tenfold. The calculated ratio corresponds approximately to 70 kg of water per m² of pack ice, precipitable in the form of 1.6 mm of rain equivalent per year. “Our analysis (…) means that by 2080, an Atlanticized and ice-free Barents Sea will be a major source of winter humidity for continental Europe” concludes the study in its summary.

* See also our article on climate change in France.

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