You will listen to part of a lecture and answer a question about it. After you h

Now listen to part of a lecture in a geology class.
    Have any of you ever noticed how cities and urban areas seem much hotter than rural areas? It may surprise you to find out that there’re many well-documented reasons for this phenomenon, which in the scientific community is called urban heat island effect. An urban heat island is a metropolitan area that’s significantly warmer than its surrounding rural areas due to human activities. There’re several factors that contribute to the drastic temperature difference between urban and rural areas. Let’s look at two examples so that you can better understand what an urban heat island is.
    One factor that contributes to hotter cities is the construction materials used for houses, roads and other urban developments that have very different thermal properties and coloration compared to grass and other vegetation. As a result, more of the incoming solar energy goes directly to heating the blacktop roads, concrete sidewalks and buildings in cities. Additionally, objects dark in color will absorb more sunlight than light-colored objects. This allows the air temperature to rise more rapidly in the cities. During night, the stored heat energy in roads and other structures is slowly released into the air, which slows the cooling process. This keeps cities warmer than rural areas at night as well as during the day.
    Another contributing factor to urban heat island effect is heat emissions from machinery. Vehicles, factories and air conditioners add more heat to the atmosphere and further intensify the heat island effect. Vehicles in particular have a significant impact on heat island effect. Firstly, heat is a byproduct of engine combustion, meaning that a running car will produce heat. Secondly, vehicle emissions, gases that are a result of combustion, contribute to the greenhouse gas effect and further exacerbate the problem of urban heat islands. It’s no wonder that when summer comes, a lot of people leave the city for a short vacation to escape the heat.