Carbonization of Urban Areas

Abstract

Re-carbonization of forests and agricultural land along with carbon dioxide (CO₂) capture technologies have been considered as options for reducing atmospheric CO₂ concentrations. Can also land ecosystem created by humans like urban areas be carbonized? The urbanization trends show that the area and importance of urban areas continue to increase. Share of urban population will increase from present 50–70% by 2050 globally. The share of urban land will be also progressively increasing to accommodate the growing number of urbanites. This chapter discusses strategies to carbonize urban areas, so that more carbon (C) per capita can be stored there. It starts with a brief review of the urban C cycle. Two features distinguish urban C cycle from other ecosystems: (1) C cycling of a city and its footprint are intimately linked and (2) natural and anthropogenic components of urban C cycle are equally important and interdependent. Then major pools and mechanisms for C storage in both anthropogenic and natural components of the urban C cycle are reviewed. Soil is the largest potential C pool followed by vegetation, landfills, and buildings. Although in settlements with low build-up density soil may store more than 60% of total C, in densely build-up cities soils and buildings may store equal amounts of C (∼40% each). Potential of C storage in landfills is controversial, because of accompanying methane emissions and groundwater pollution. Human-driven mechanisms for C accumulation in cities such as import of C containing materials supersede the natural ones. At the current level of technology any option for carbonization of cities is associated with CO₂ emissions. Cities’ carbonization cannot be considered as a pure increase in C storage per capita, but as an increase in C storage per capita per unit of emitted CO₂.