methods to understand the phenomenon. In 1929, Albert Peppler used the term believed to be the first instance of an equivalent to urban heat island, "staedtischen Waermeinsel." Between 1990 and 2000, about 30 studies were published annually; by 2010, that number had increased to 100, and by 2015, it was more than 300. Beginning in the 2020s, a number of cities worldwide began creating Chief Heat Officer positions to organize and manage work counteracting the urban heat island effect. Causes There are several causes of an urban heat island (UHI); for example, dark surfaces absorb significantly more solar radiation, which causes urban concentrations of roads and buildings to heat more than suburban and rural areas during the day; materials commonly used in urban areas for pavement and roofs, such as concrete and asphalt, have significantly different thermal bulk properties (including heat capacity and thermal conductivity) and surface radiative properties (albedo and emissivity) than the surrounding rural areas. This causes a change in the energy budget of the urban area, often leading to higher temperatures than surrounding rural areas. Another major reason is the lack of evapotranspiration (for example, through lack of vegetation) in urban areas. The U.S. Forest Service found in 2018 that cities in the United States are losing 36 million trees each year. With a decreased amount of vegetation, cities also lose the shade and evaporative cooling effect of trees. Other causes of a UHI are due to geometric effects. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. This is called the "urban canyon effect". Another effect of buildings is the blocking of wind, which also inhibits cooling by convection and prevents pollutants from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the UHI. High levels of pollution in urban areas can also increase the UHI, as many forms of pollution change the radiative properties of the atmosphere. UHI not only raises urban temperatures but also increases ozone concentrations because ozone is a greenhouse gas whose formation will accelerate with the increase of temperature. For most cities, the difference in temperature between the urban and surrounding rural area is largest at night. While temperature difference is significant all year round, the difference is generally bigger in winter. The typical temperature difference is several degrees