Activities in the metropolitan areas affect major atmospheric systems and either warm or cool areas further away.
The study by scientists at the Scripps Institution of Oceanography, University of California, San Diego; Florida State University; and the National Center for Atmospheric Research was funded by the National Science Foundation, NCAR’s sponsor, as well as the Department of Energy and the National Oceanic and Atmospheric Administration.
The results indicate that cars and buildings in major cities in the Northern Hemisphere are the main contributors to the increase in temperatures in many remote areas of the U.S. In Europe, on the other hand, changes in atmospheric circulation result in decrease in temperature.
Globally, the average increase worldwide is estimated to be 0.01 degrees C (about 0.02 degrees F). However, on regional scale, there are some areas where warming is much higher than what has been predicted.
According to Aixue Hu, NCAR scientist and one of the co-authors of the study, burning fossil fuels has double impact- it releases greenhouse gases, and it produces heat that escapes from the sources. Although the heat is concentrated in urban areas, atmospheric currents and patterns carry it away.
The scientists distinguished the effect of the so-called waste-heat from the heat island effect, where it is collected and re-radiated by pavements and constructions. The team analyzed energy consumption, which generates waste heat, and used a computer model to simulate the atmospheric effects and the influence of the heat.
They found that collective heat from a number of urban areas can affect temperatures thousands of miles away from these regions. The problem is strengthened by the fact that in the Northern Hemisphere, urban areas are located under troughs and jet streams.
The East and West coasts of the North American and Eurasian countries are known to be the most populated and energy-intensive urban areas and the most intensive atmospheric circulation. The release of waste heat interrupts the normal circulation system and therefore changes the temperatures in a great distance from the heat sources, according to the authors.