Urban regions a good 2°C warmer than rural regions
Among other factors, German professor Fritz Vahrenholt looks at the urban heat island effect.
By Fritz Vahrenholt
In August 2023, the deviation of the global temperature from the 30-year average of the satellite-based measurements of the University of Alabama (UAH) continued to increase slightly compared to July. The value is 0.69 degrees Celsius and represents the second highest deviation from the long-term average since 1979.
The temperature increase has averaged 0.14 degrees Celsius per decade since 1979. A further rise of this magnitude is no cause for concern, certainly not for panic. The increase in ocean temperature has been 0.12 degrees Celsius per decade; the increase in land temperature has been 0.19 degrees per decade. We will elaborate on why land temperatures are rising.
The heat island effect results when measuring stations that were once located in purely rural areas now find themselves surrounded by populated areas due to urbanization.
Rural vs urban
An example is the Frankfurt Airport measuring station, which 80 years ago had rural areas as its surroundings, but is now influenced by heat-storing and heat-emitting runways, highways, buildings and traffic.
The study concludes that 65% of the 1850-1900 rural monitoring stations are now fully urbanized. Why is this important? The difference in temperature between urban and rural areas is serious; if rural areas become urbanized over time, the respective local monitoring stations will record the higher temperature of the urbanized environment. Accordingly, the locations of the measuring stations have a more important role in the assessment of the global temperature increase than previously thought.
Yearly mean temperatures in rural regions of Munich (gray) and Munich City (blue). Source: Lüning/Vahrenholt Unerwünschte Wahrheiten (Unwanted Truths) 2021.
Since the ratio of measuring stations in the countryside and in the city has shifted by 65% in favor of the cities due to growing cities, this also has an influence on the causes of the global temperature development.
Therefore, part of the warming of the last 150 years in Europe, the USA and, above all, China is due to changes in the environment and not solely to rising CO2 concentrations.
The study concludes that the effect is 0.34 degrees Celsius per century. This does not absolve CO2, but the degree of warming on land would be almost 40 % lower without the heat island effect.