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Hot and bothered

Hot and bothered

In June 2019 Poland was hit by a heatwave. Scientists believe that the global warming finally starts to take its toll. Dr hab. The issues of the climate change and record high June temperatures in Polish cities are discussed by Prof. Agnieszka Wypych from the JU Department of Climatology.

In recent years, a number of scientific reports, including those by the Intergovernmental Panel on Climate Change (IPCC) or the conferences of the parties of the United Nations Framework Convention on Climate Change have pointed to the impact of the ongoing climate change. The alarming effects of this process have also been a frequent focus of the mass media and numerous NGOs.

The changes, characterised as the global warming, are perceived as detrimental from both environmental and economic point of view and hence various political and administrative bodies have taken measures to counter them. At the same time, there have been attempts to adapt societies to the changing conditions, to ensure the safety and comfort of their members.

In order to indentify the symptoms of climate change, weather conditions are closely monitored, with special focus on the changes in air temperature and rainfall at different geographic and temporal scales. This allows researchers to decide to what extent the ongoing changes are significant, what the major trends are and whether they may be characterised as extreme. For instance, June 2019 can be identified as a symptom of such trend, since it was exceptionally hot in Central Europe, including Poland.

Temperature record broken

Fig.1 Average monthly air temperature in June 2019 (source: http://klimat.pogodynka.pl/)

It’s worth noting that June is the coldest month of the so-called climatological summer (June, July, and August), with average air temperature of about 16-17ºC and sunshine duration of circa 220 hours. Yet, in 2019 it was much warmer than that (Figure 1).

This year, many parts of Poland experienced the hottest June since the records began. This refers not only to the average air temperature but also its highest values. In Radzyń, Lubusz Province, the temperature on 26 June 2019 reached 38.2ºC, breaking the national June temperature record. The hottest day in Kraków was 30 June, when the station at the Jagiellonian University Department of Climatology recorded the highest June temperature since 1792, when the records began: 35.8ºC. Outside the city centre it was a little bit “cooler”: 34.9ºC in Wola Justowska and 34.2ºC in Balice (Figure 2 and 3).

 

 

 

Fig. 2 Maximum and minimum June air temperature in 2019 in Kraków (Kraków-Balice weather station) compared to the period 1951-2018. The lines show the maximum and minimum daily air temperature in June 2019, whereas the bars illustrate the lowest (blue) and highest (red) daily temperatures in the period 1951-2018.

Fig. 3 Changes in average June air temperature (Tśr) and mean maximum June air temperature (Tmax)  in Kraków (Kraków-Balice weather station, 1951-2019)

Abnormal June

Fig. 4 Anomalies of monthly mean air temperature in June 2019 compared to the reference period 1981-2010  (source: http://klimat.pogodynka.pl/)

When compared to the period 1981-2010, recommended by the World Meteorological Organisation as the standard reference period, weather in June 2019 can be definitely considered abnormal. The sunshine duration was 150 hours longer (in Western Poland) or 130 hours longer (in Central Poland) than the aforementioned average. The heatwave which affected most of the country resulted in maximum temperature being 7 degrees above the norm and average temperature being 5 degrees above the norm (Figure 4).

The air temperatures recorded in Poland in June 2019 fully reflect the tendencies observed throughout the Northern Hemisphere. Figure 5 shows June temperature anomalies along with the rising linear trend of 0.13ºC/10 years in Europe.

 

 

 

 

 

Fig.5 Air temperature anomalies in June on the Northern Hemisphere (NH) and in Europe (EUR) during the years 1910-2018 compared to the period 1910-2000. Straight lines – linear trends (source: https://www.ncdc.noaa.gov/cag/)

Hot June means hot summer?

Is hot June 2019 a result of the changing climate conditions? And does it mean that the entire summer will be proportionally hotter?

The exceptionally hot weather in June 2019 has often been described as one of the symptoms of the global warming. However, many climatologists warn against jumping to conclusions. Even in recent history, the series of extremely hot and dry seasons were followed by exceptionally cold and rainy ones. In Poland, for instance, after the hot and dry summers of 1992 and 1994, when many scientists pointed to the persistent problem of drought, came the devastating flood of July 1997. This year’s May also turned out to be very cool and wet, which reflects the changeability and instability of weather conditions.

Besides the human activity, whose role in the climate change is rarely disputed, there are other, natural factors that have had impact on the amount of solar energy reaching the earth and, consequently, on weather trends, for millions of years. In addition to the astronomical factors, such as the orbit parameters, the Earth’s axial tilt, and precession, changing in cycles of several dozen or several hundred years (known as Milankovitch cycles), they include the solar factors, such as sunspots, the volcanic activity, and, finally, the atmospheric circulation, which is directly reflected in the changing weather conditions.

It’s the atmospheric circulation that was responsible for the extreme weather in June 2019 in Poland. The synoptic situation in Europe during most of June was determined by the influx of very hot air from the south. The high-pressure centre located over the European part of Russia caused the advection of tropical masses of hot air.

Original text: www.nauka.uj.edu.pl

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