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CWA # 836, 26 November 2022

Europe: Heatwaves, Wildfires, Droughts, and Ice Melt in Alps
Major causes behind Europe’s continuing heatwaves

  Padmashree Anandhan

Europe was plagued by intensive heatwaves during the summer due to adverse effects of climate change

Since 1920’s, Europe began to experience extreme high temperatures in the air, land, and sea surfaces leading to life threating climate disasters such as heatwaves, wildfires, droughts and flash floods. In the present the extent of damages has scaled up causing severe challenges to lifestyle and European economies. The commentary aims to study the geographic spread of the heatwaves, tracing the highest occurrence in Europe since the 1980 and will provide the causes behind Europe’s continuing heatwaves.

Geographic mapping
First record of high temperatures was seen in July following into August. Now, the European Centre for Medium-Range Weather Forecasts (ECMWF) predicts the temperature to persist till October, marking the longest period of heatwaves since 1980. As per the weather anomaly chart of ECMWF, the temperature has increased to 10 degrees Celsius above average in (46) Portugal, (45) northern Spain, (40) western France, and southern England. With the hot air moving north, the Benelux countries, Baltic region, Ireland, (40.3) the UK, Belgium, Luxemburg, the Netherlands, northern Italy, Switzerland and western Germany recorded six-degree Celsius high than the average temperatures. In case of the Northern Europe, it is expected to heat up by three degrees Celsius. As per European Space Agency using Sentinel 2 & 3 (Earth observatory satellite), separated air, and land surface temperatures and found that the land surfaced amounted for 55 degrees Celsius due to increasing weather and climate shifts. While the “slow-moving high pressure” pushes the hot air from North Africa, it sways into western and central Europe affecting the Benelux. The northerly winds from Scandinavian and southerly winds from Ural Mountains have created heatwaves over Russia, extending to western and eastern Siberia. Overall, the western Europe, western Siberia, eastern Siberia and Russia are marked as four hotspots experiencing heatwaves through double jets from 2010-2020.

In terms of the sea surface temperatures, all five European seas, Black Sea, Baltic Sea, Mediterranean, North Sea and the North Atlantic began warming since 1870. Mediterranean Sea is observed to be the warmest of all. As per the Copernicus Ocean State Report 5, the Mediterranean Sea is most affected by marine heat waves as the area has experienced significant warming over the last decades. An increase in the temperature of the eastern Mediterranean Sea in 2019 contributed to a northern spread of invasive lionfish, Pterois miles, through the Suez Canal – an invasive migration that had relatively declined in 2018. As far as the Arctic Ocean, the surfaces have shown a slow heating trend, whereas the land surrounding the Arctic showed a faster trend in rising temperatures. Although the source link between the increasing sea temperatures and the adjacent effect on land is being studied, now scientists have only found the carbon sequestering capacity of the oceans to have lost its pace to keep up since 1990’s, impact on the living species and the doubling marine heatwaves compared to land surface temperatures. Therefore, marine heatwaves have varying impacts on the growth, reproduction, and behavior of specific marine species, impacting their populations as well as their catches.

Recent occurrences
When it comes to Europe, in the 20th century, the extreme weather conditions are nothing new as it started in 1920, which was a dry autumn and a winter first affecting the water supply, agriculture, and livestock farming. This developed into wildfires, severe drought and dry hazards in England, the Czech Republic and parts of central Europe. Such phenomenon continued through the summers of 2003, 2010, 2015. Later, with rise in global temperatures, soil moisture deficit and increase in GHG’s turned the hot summer to occur frequently from 2018, 2019, 2020, and 2022. The first severe heatwave which began in 2003 recorded 35 to 40 degrees Celsius according to the UNEP data. It was caused due to anti-cyclone in the western Europe, which blocked the “rain- bearing depressions” that enter from the Atlantic Ocean. Thereby resulting in hot air across the Mediterranean, western, central and parts of southern Europe. The impact was majorly felt in agricultural production, Alpine glacier melting up to 10 per cent and energy needs. After 2003, 2015 was when the temperatures hit the peak, where the range increased from the 35 degrees margin to 36.7 degree Celsius, with 39.7 degree marked the highest in Paris.

All five European seas, Black Sea, Baltic Sea, Mediterranean, North Sea and the North Atlantic showed rapid warming from late 1970s. Between 1982 and 2018, Sea surface temperature increased by between around 0.3°C per decade, in the North Atlantic, and around 0.6°C per decade, in the Black Sea. Although the increasing trend is expected to go further, it is slow when compared to the air and land temperatures. The frequency and magnitude of marine heatwaves have increased significantly both globally and in European seas and is projected to continue, with increasing expected impacts on climate and ecosystems.

During 1925 to 2016, along with the increase in Sea surface temperatures, there was an increase in the frequency and intensity of marine heatwaves, in European seas. Which has resulted in ecological impacts, promoting harmful algal blooms, increased risks to human health, and aquaculture. For example, recent marine heatwaves led to vibriosis infections along the Baltic Sea and North Sea coasts. Marine heatwaves also affect the climate on land, with those in the Mediterranean Sea being thought to have contributed to amplifying heatwaves and heavy precipitation events over central Europe and triggering intense weather anomalies. Which can be now seen in the southern France, Greece, Italy, Portugal and Spain located facing the climate extremes.

Causes
Jet stream/double jets
The causal factors for the heatwaves and rising temperatures are mainly caused due to the increased human activities and rising global temperatures, but the high concentration of Carbon dioxide gases, flow of jet stream where the hot air from Africa, circulation of atmosphere and the ocean is attributed to Europe. As far as analysing the heatwaves, no two heatwaves were observed to be of same nature but differed in temperatures due to “upper level low- pressure air” which is called as the “cutoff low” where the cut off from a river of westerly winds, the mid-latitude jet stream, that circles the planet at high altitudes. Low- pressure zones tend to draw air toward them. In this case, the low-pressure zone has been steadily drawing air from North Africa toward it, thereby pumping hot air northward into Europe. A study published in Nature communications keeping Europe as the center of heatwave hotspot found that increased occurrence of double jet marking the extreme heat since 2003 heatwave. As per Observational and model-based studies have discovered the cause behind the raise in temperatures to be “blocking anti- cyclones,” which act as high-pressure system creating double-jet stream. Such flow of double jets can soon become more common when zonal flows are weakened under Arctic amplification.

The scientists from Potsdam Institute of Climate Impact Research (PIK) were able to find out the reason behind 35 per cent of the extreme heatwaves in Western Europe, which were due to continuing double jets.

According to experts from ECMWF, heatwaves can be the result of a stationary high-pressure system with clear skies and weak winds. These conditions can create longer heatwaves, such as the recent one in mid-August,” Florian adds. “The effect on near-surface temperature depends on how much energy is used to evaporate water from the ground and plants, and how much is heating the air. If the soil is already dry or the surface is just concrete and tarmac, there is little cooling of the near-surface temperature due to evaporation. Instead, most of the energy will heat the air and thus increase the magnitude of the heatwave.”

Rise in sea temperatures
The slow increase of water temperatures due to long-term anthropogenic change and increased occurrences of marine heat waves have been having devastating effects on local ecosystems. Marine heat waves have also been associated with the likelihood of extreme weather events, such as cyclones and heavy precipitation. The rise in ocean temperature is one of the major drivers for migration of marine species to higher latitudes. More subtropical and tropical marine species are replacing temperate water fish, reshaping fisheries and catch compositions. Mediterranean Sea being the warmest of all, single jets have been one of the causes for its rising temperatures and changes in the local land atmosphere along with its combination with soil preconditioning. Whether is it having a direct influence over rising land surface temperatures, Mediterranean Sea, influence on the moisture balance and its role in the regional hydrological cycle is substantial. Warmer Mediterranean SSTs lead to enhanced evaporation and moisture transport in the atmosphere. Therefore, making this region a major climate change hot spot for the coming decades.


About the author
Padmashree Anandhan, is a Project Associate at the School of Conflict and Security Studies, NIAS.

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