81 On the urban heat islands and their possible impact on climate. A.P. Nickolaenko 1 and I.G. Kudintseva 2 Usikov Institute for Radio-Physics and Electronics National Academy of Science of the Ukraine, Kharkov, 12, Acad. Proskura Street, Ukraine Karazin Kharkov National University, Kharkov, 4, Svoboda Sq., Ukraine Abstract. Our paper estimates possible impact of urban civilization on the global climate. An effective model is used of the “heat island” centered above the city, it describes the temperature distribution over the urban area of a radial-circular structure. Contribution was estimated of the big cities into the median temperature of the Earth. It is shown that heat production in the radial-circular cities is able to deteriorate the life conditions at the center of a city with great population. According to the model, contribution from the update cities into the global median temperature is evaluated as ~0.04 C. Simultaneously, a thousand of cities of the 10 million inhabitants each is able to raise the global median temperature by 0.4 C. Key words: city heat island, diffusion equation, global temperature 1. Introduction. It is known that the air temperature is higher over all big cities in comparison with the surrounding territory. Usually, we say that a city creates a “heat island” in the nearby atmosphere. This heat spreads over the planet and raises the overall temperature. We will not address the details of the heat exchange between different parts of atmosphere or above the various kinds of landscape. Instead, we follow an obvious idea that the excessive temperature of urban areas must contribute into the global warming. The question is: what the effect might be when the abundant heat is uniformly distributed over the planet? We introduce some “effective” characteristics of a settlement as the heat source and compare them with the published observational data. By using the equation of heat diffusion, we obtain formal estimates for additional temperature as a function of city size. Finally, we choose the realistic models and evaluate possible contribution from urban structures into the planetary temperature. Thus, we evaluate an extent to which the modern civilization might influence the climate on the global scale. 2. City population and heat production. We assume that a citizen occupies a standard area of S 1 = 3030 m 2 . This is not the area of a dwelling or of the individual land patch: this is the average area of the city territory relevant to a single inhabitant. By using this standard area of 900 m 2 , one obtains the realistic size of a city with a definite population P. Since the urban area S is directly proportional to the population, we have the following relation: S = S 1 P (1) As a result, the linear size of a settlement grows as a square root of its population. Indeed, a city of the radial-circular structure will have the radius a = (S 1 P/) 1/2 (2) Journal of Atmospheric Electricity, Vol.33, No.2, 2013, pp.81-89. Copyright 2013 by the Society of Atmospheric Electricity of Japan.