Global warming and the urban heat island

Abstract

The aim of this paper is not to present an exhaustive synthesis of the literature addressing global warming and the urban heat island; rather, it is to shed light on some common misperceptions and to address this issue by presenting a number of different perspectives and by highlighting some of the topics that require further research. By 2005, in the most developed countries of the world, ∼74% of the population lived in urban areas. Between 2005 and 2010, the world's urban population is predicted to grow at an annual rate of 1.96%. By 2015, cities with over 10 M inhabitants ("megacities"-see also Kraas, this volume) will account for 9% of the total urban population (http://esa.un.org/unup/, [as of 10 Nov 2006]). However, urban growth incorporates two other trends: income growth and spatial growth or sprawl (Kahn 2006). The flight to the cities has been exacerbated not only by the effects of desertification, reductions in biodiversity and soil fertility in the rural areas, and the effects of globalization, especially in third-world nations (Handay et al. 1992, cited by Oke 1997), but also by income growth, especially in developed countries. As income grows, the urban population tends to sprawl (Kahn 2006). According to Mills (2006), the new urban utopia is the sustainable city, whose impacts upon the environment are minimized without bringing about a reduction in the quality of life of the urban dwellers (Newman 1999; Kamp et al. 2003). Sustainable development is therefore the most important aim of the urban planning process (Barton 1996), because severe environmental problems, such as poor air and water quality, noise and thermal stresses, are especially likely in cities. Today's urban sprawl has led to worsening environmental problems, as more area is sealed over (i.e., becomes impermeable through paving or building construction), less green area remains, and water and energy consumption increase (Kahn 2006). As a result, ever more serious local, regional and even global threats have been emerging (Oke 1997; Decker et al. 2000). Many titles in the scientific literature refer either to global warming (GW) or to urban climate, the latter including in particular the issue of urban heat islands (UHI). However, there are few papers or books that address the relationships between GW and UHI. Differences in temporal and spatial scales, research methods and data sets, as well as the lack of a comprehensive theoretical framework, are responsible. However, a better understanding of the role urban areas play in GW is an urgent concern, so that one might fight the negative consequences of GW and to take necessary measures to mitigate those consequences or to adapt to new climate conditions. On the other hand, the impact of GW upon urban thermal climates is also poorly understood and is often the object of many overly simplistic and erroneous ideas. © 2008 Springer Science+Business Media, LLC.