Much of today's environmental impacts originate in cities

Published: Saturday 15 March 2008

Urban socioecosystem as a driv Down to Earth The world has seen a dramatic shift to urban living. In 1900, only 10 per cent of the global population were urban dwellers; now it's more than 50 per cent. More than 95 per cent of the net increase in global population will be in cities in the developing world

Down to Earth Cities are both drivers of and responders to environmental changes in rapidly developing countries like China and India. Unprecedented growth in urban population over the past century has occurred in less than 3 per cent of the global terrestrial surface. But their impact has been global, with 78 per cent of carbon emissions, 60 per cent of residential water use and 76 per cent of wood used for industrial purposes

Down to Earth
Change in population of the 10 largest urban centres from 1950 to 2010 (projected)
Down to Earth Perceived opportunities in growing urban centres and lack of opportunities in rural settings resulting from degraded landscapes and economic imbalances have triggered migrations since 1950 and the trend continues.The concentration of transportation and industry in urban centres means that cities are sources greenhouse gases that cause climate change

Down to Earth In the past two decades, there has been large increase in the output of materials such as the food-waste and solid waste accumulation and growth in demand for building materials

Down to Earth Cities show symptoms of the biogeochemical imbalances that they help create at harsher scales.For example, cities experience high acid and high concentrations of atmospheric CO2, CH4 and O3

Down to Earth City centres are physically hotter.Known as the heat island effect, urban and suburban temperatures are 1 to 6C hotter than nearby rural areas, says the us Environmental Protection Agency. Just one-degree rise in temperature can increase residential water use 1098 litres per month on average for a family

Down to Earth
Change in world urban and rural population (in per cent) from 1950 to 2030 (projected)
Down to Earth The top-down influence of global climate change on cities may be overshadowed by local changes in climate that accompany urbanization

Down to Earth Within cities, urbanization and allied changes reduce species diversity and evenness. For example, urban sprawl in northern latitudes appears related to declines in abundances in some migratory birds in southern latitudes

Down to Earth Cities are also hot spots for solutions and problems. Urban ecology has a pivotal role in finding those solutions and navigating for a sustainable urban future

Source: Global change and the ecology of cities, published in Science, February 8, 2008 by Arizona State University ecologist Nancy Grimm and colleagues

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