ABSTRACT
The land surface of our home planet Earth is a finite resource that is central to human welfare and the functioning of Earth systems. Human population growth is one of the major global-scale forcing that underlie the most recent global-scale state shift in Earth’s biosphere (Barnosky et al. 2012). Due to industrialization, economic growth, technology advances, and population explosion, human activities worldwide are transforming 290the terrestrial environment at unparalleled rates and scales. Prime grasslands and forests have been converted to croplands and pastures, which cover about 40% of the global land surface (Foley et al. 2005), to support the rising need for food by more than 7 billion people (UNFPA 2011). Among anthropogenic activities, urbanization is the most irreversible and human-dominated form of land use, modifying land cover, hydrological systems, biogeochemistry, climate, and biodiversity worldwide (Grimm et al. 2008). Worldwide, urban expansion is one of the primary drivers of habitat loss and species extinction (Hahs et al. 2009). Urban areas also affect their local climates through the modification of surface albedo, evapotranspiration, and increased aerosols and anthropogenic heat sources, thereby creating elevated urban temperatures (Arnfield 2003) and changes in regional precipitation patterns (Marshall Shepherd et al. 2002; Rosenfeld 2000; Seto and Shepherd 2009). In many developing countries, urban expansion takes place on prime agricultural lands (del Mar López et al. 2001; Seto et al. 2000). Although occupying about only 2% of the global land surface (Akbari et al. 2009), cities worldwide are now hosting more than 50% of the world population (Heilig 2012), producing more than 90% of the world gross domestic product (GDP) (Gutman 2007), consuming more than 70% of energy (Nakicenovic 2012), and generating more than 71% of anthropogenic greenhouse gas emissions (Hoornweg et al. 2010). However, cities also show themselves as a potential solution to climate change through efficient resource use. Compact urban development coupled with high residential and employment densities can reduce energy consumption, vehicle miles traveled, and carbon dioxide emissions (Gomez-Ibanez et al. 2009). Per capita energy use and greenhouse emissions are often lower in cities than national averages (Dodman 2009). Furthermore, increasing urban albedo could offset greenhouse gas emissions (Akbari et al. 2009).
