Fewer Days Of Extreme Cold And More Days Of Extreme Heat In Europe

ScienceDaily (Jan. 31, 2009) — Scientists from the Complutense University of Madrid (UCM) have selected 262 European observatories which analysed the series of minimum and maximum daily temperatures from 1955 to 1998 to estimate trend variations in extreme temperature events. According to the study, in Europe days of extreme cold are decreasing and days of extreme heat increasing. From 0.5ºC to 1ºC in the average minimum temperature, and from 0.5ºC to 2ºC in the average maximum temperature.

Continuous rises in annual temperatures in certain areas lead to “changes in the environment and significant increases in the frequency of values considered extreme temperatures,” SINC was told by Emiliano Hernández, Professor of Atmospheric Physics at the UCM and one of the study's authors. To reach this conclusion, the scientists worked with 135 stations with a daily series of minimum temperatures and 127 stations with a daily series of maximum temperatures, located in 34 European countries.

The study, recently published in the journal Atmosfera, looked at temperatures from January 1, 1955 to December 31, 1998, and analysed the pattern of extreme temperature days in Europe. “All the series of temperatures have been homogenised to eliminate possible discontinuity points, and highlight any factor that is not meteorological or climatic,” the physicists pointed out.

Higher frequency of days of extreme heat

During the 44 years of analysis, the researchers recorded extreme cold events (between the months of November and March) and extreme heat events (from June to September) noting a slight decrease in days of extreme cold and increase in days of extreme heat,” commented Hernández.

65.2% of the stations that measured minimum temperatures showed that these temperatures have been increasing, while 40% of the stations that measured maximum temperatures showed that these temperatures have risen too. Observatories that detected these trends are located in Western Europe, including the British Isles and Iceland for both extreme cold days and extreme heat days.

“The reduction in days of extreme cold is due to an increase in the average minimum temperature from 0.5ºC to 1ºC during the analysis period, while for days of extreme heat, the increases in the average maximum temperature were from 0.5ºC to 2ºC,” the scientists explained.

The decrease in days of extreme cold and increase in days of extreme heat are due to both local and global factors, according to the scientists. Some of them include the heat island produced in cities or the change in the general circulation of the atmosphere which directly determines extreme temperature events.

The danger of heatwaves

Apart from their direct relationship with climate change, extreme temperatures (minimum and maximum) particularly affect human health. The scientific community has explained on numerous occasions that the impact of heatwaves is far greater than that of minimum temperatures.

Since 1860, the planet's average temperature has increased by 0.60ºC. “In particular, in the 2003 heatwave, which affected most of Europe, the average temperature was 3°C more than the normal value for the summers from 1961 to 1990 with the most significant increases being in central France, Switzerland, northern Italy and southern Germany,” stressed Marco Cony, co-author of the study and physicist at the UCM.

An example of the effects of days of extreme heat, which will increase in frequency, is the heatwave that hit Europe in 2003. That summer record maximum temperatures were recorded in monthly, weekly and daily scales. For example, in Switzerland a temperature of 41.50ºC was recorded while in Portugal, 47.30ºC.

Experts warn that excessive heat can cause stress, worsening of diseases and even death, such as in the summer of 2003, when over 30,000 people died throughout Europe from the high temperatures.

Journal reference:

1. Cony, M.; Hernández, E.; Del Teso, T. Influence of synoptic scale in the generation of extremely cold days in Europe. Atmosfera, 21(4): 389-401, October, 2008