The Central Role of Energy in the Urban Transition: Global Challenges for Sustainability

The urban transition, the increased ratio of urban to rural population globally and within countries, is a hallmark of the twenty-first century. Our analysis of publicly available data from the World Bank spanning several decades for ~ 195 countries shows that across and within nations over time, per capita Gross Domestic Product (GDP), energy use, and CO2 emissions are lowest in predominantly rural countries (rural > urban pop.), increase rapidly across urbanizing countries (rural ≈ urban pop.), and are highest in the most urban countries (rural < urban pop.). These trends coincide with changes in employment by sector and gender. Rural economies are based largely on employment in the resource-extraction sector, which includes agriculture, fisheries, forestry, and mining. In urbanizing nations, male employment is predominantly in the industrial sector, including public utilities, while female employment is higher in service-based than resource-based economies. In the most urban nations, service economies predominate with some countries employing 90% of women and 65% of men in the service sector. Our analysis shows that per capita GDP, energy use, and CO2 emissions increase by over two orders of magnitude from low-income, resource-based rural countries to high-income, urbanized countries with predominantly service economies. Data from the U.S. over the past 200 years illuminate a socio-metabolic urban transition similar to that seen globally in recent decades across countries and through time. Our study suggests that increased energy demand and climate consequences of burning fossil fuels will continue to accompany a rapidly urbanizing planet posing major challenges for global sustainability.