Challenges in the 21st century

Human society is entering into an increasingly urbanized era. City dwellers accounted for 54% of the world’s population in 2014 (United Nations, 2015). Land changes from green spaces to impervious surfaces to support the demands of increasing urban populations. Meanwhile, cities account for 78% of carbon emissions, 60% of residential water use, and 76% of wood used for industrial purposes (Grimm et al., 2008). Urbanization leads to various changes in the environment such as urban heat island (Zhou, Zhao, Liu, Zhang, & Zhu, 2014), atmospheric chemistry (Pan et al., 2016), hydrology (Suriya & Mudgal, 2012), biogeochemical cycles (Kaye, Groffman, Grimm, Baker, & Pouyat, 2006), and biodiversity including species homogeneity (Hope et al.,2003; Valiela & Martinetto, 2007). These changes are rightly surrogates for the most significant global environmental changes (IPCC, 2013). The various changes in urban environments have made cites ideal natural laboratories for global change studies (Farrell, Szota, & Arndt, 2015; Grimm et al., 2008; Zhao, Liu, & Zhou, 2016). Using urban habitats around the globe to develop and test hypotheses on future climate change impacts would complement manipulative experiments and predict how ecosystems would be altered in the future (Youngsteadt, Dale, Terando, Dunn, & Frank, 2015).