The Role of Urbanization in the Global Carbon Cycle

Urban areas account for more than 70% of CO2 emissions from burning fossil fuels. Urban expansion in tropics is responsible for 5% of the annual emissions from land use change. Here, I show that the effect of urbanization on the global carbon cycle extends beyond these emissions. I quantify the contribution of urbanization to the major carbon fluxes and pools globally and identify gaps crucial for predicting the evolution of the carbon cycle in the future. Urban residents currently control ~22 (12–40)% of the land carbon uptake (112 PgC/yr) and ~24 (15–39)% of the carbon emissions (117 PgC/year) from land globally. Urbanization resulted in the creation of new carbon pools on land such as buildings (~6.7 PgC) and landfills (~30 PgC). Together these pools store 1.6 (±0.3)% of the total vegetation and soil carbon pools globally. The creation and maintenance of these new pools has been associated with high emissions of CO2, which are currently better understood than the processes associated with the dynamics of these pools and accompanying uptake of carbon. Predictions of the future trajectories of the global carbon cycle will require a much better understanding of how urban development affects the carbon cycle over the long term.Peer Reviewe

The influence of landcover change on global terrestrial biogeochemistry

Discussions concerning global change typically concentrate on future climatic changes promulgated by changes in atmospheric chemistry, most notably increases in the so-called greenhouse gases such as CO2, CH4, and and N2O. Although the energy exchange characteristics of the Earth’s surface are an important component of climate models, the idea that changes in the terrestrial surface could also be a causal factor in climatic changes has not received much attention. Sensitivity studies with GCM’s suggested that regional climate can be dramatically changed by severe deforestation. Dickinson and Henderson-Sellers (1988) simulated the Amazon basin with complete forest cover, and then replaced with degraded grasslands. Th degraded grasslands reduced evapotranspiration so much that surface temperatures were predicted to increase by 3-5 degrees. Walker et al. (1995) used the deforestation statistics of Skole and Tucker (1993) and estimated that precipitation had been reduced by 1.2mm/day due to reductions in ET of 18% caused by landcover changes