Query: While urban areas are undoubtedly warmer than surrounding rural areas, this has had little to no impact on warming trends.

Relevant passages:
Urban heat island <=SEP=> An urban heat island ( UHI ) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities . The temperature difference usually is larger at night than during the day , and is most apparent when winds are weak . UHI is most noticeable during the summer and winter . The main cause of the urban heat island effect is from the modification of land surfaces . Waste heat generated by energy usage is a secondary contributor . As a population center grows , it tends to expand its area and increase its average temperature . The less-used term heat island refers to any area , populated or not , which is consistently hotter than the surrounding area .   Monthly rainfall is greater downwind of cities , partially due to the UHI . Increases in heat within urban centers increases the length of growing seasons , and decreases the occurrence of weak tornadoes . The UHI decreases air quality by increasing the production of pollutants such as ozone , and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems .   Not all cities have a distinct urban heat island . Mitigation of the urban heat island effect can be accomplished through the use of green roofs and the use of lighter-colored surfaces in urban areas , which reflect more sunlight and absorb less heat .   There are concerns raised about possible contribution from urban heat islands to global warming . Research on China and India indicates that urban heat island effect contributes to climate warming by about 30 % . On the other hand , one 1999 comparison between urban and rural areas proposed that the urban heat island effects have little influence on global mean temperature trends . Many studies reveal increases in the severity of the effect with the progress of climate change .

Urbanization <=SEP=> Urbanization refers to the population shift from rural to urban areas , `` the gradual increase in the proportion of people living in urban areas '' , and the ways in which each society adapts to the change . It is predominantly the process by which towns and cities are formed and become larger as more people begin living and working in central areas . The United Nations projected that half of the world 's population would live in urban areas at the end of 2008 . It is predicted that by 2050 about 64 % of the developing world and 86 % of the developed world will be urbanized . That is equivalent to approximately 3 billion urbanites by 2050 , much of which will occur in Africa and Asia . Notably , the United Nations has also recently projected that nearly all global population growth from 2017 to 2030 will be absorbed by cities , about 1.1 billion new urbanites over the next 13 years .   Urbanization is relevant to a range of disciplines , including geography , sociology , economics , urban planning and public health . The phenomenon has been closely linked to modernization , industrialization and the sociological process of rationalization . Urbanization can be seen as a specific condition at a set time ( e.g. the proportion of total population or area in cities or towns ) or as an increase in that condition over time . So urbanization can be quantified either in terms of , say , the level of urban development relative to the overall population , or as the rate at which the urban proportion of the population is increasing . Urbanization creates enormous social , economic and environmental changes , which provide an opportunity for sustainability with the `` potential to use resources more efficiently , to create more sustainable land use and to protect the biodiversity of natural ecosystems . ''   Urbanization is not merely a modern phenomenon , but a rapid and historic transformation of human social roots on a global scale , whereby predominantly rural culture is being rapidly replaced by predominantly urban culture . The first major change in settlement patterns was the accumulation of hunter-gatherers into villages many thousand years ago . Village culture is characterized by common bloodlines , intimate relationships and communal behavior whereas urban culture is characterized by distant bloodlines , unfamiliar relations and competitive behavior . This unprecedented movement of people is forecast to continue and intensify during the next few decades , mushrooming cities to sizes unthinkable only a century ago .   Today , in Asia the urban agglomerations of Osaka , Karachi , Jakarta , Mumbai , Shanghai , Manila , Seoul and Beijing are each already home to over 20 million people , while Delhi and Tokyo are forecast to approach or exceed 40 million people each within the coming decade . Outside Asia , Mexico City , São Paulo , London , New York City , Istanbul , Lagos and Cairo are , or soon will be , home to over 10 million people .