  The urban transition, the increased ratio of urban to rural population
globally and within countries, is a hallmark of the 21st century. Our analysis
of publicly available data from the World Bank spanning several decades for
~195 countries show 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.
