The world's cities, consuming much more of the world's energy than rural regions do, are the best places to initiate efforts to mitigate emissions in order to meet climate goals, a study says.
The study of 274 global cities noted that 53 percent of the global population -- some 4 billion people -- live in towns and cities rather than in rural areas, a trend certain to accelerate with a growing world population.
Cities are responsible for most of the world's energy consumption -- from 67 to 76 percent -- and emit around three quarters of total world carbon emissions, researchers from the U.S. and Germany report in the Proceedings of the National Academy of Sciences.
That suggests cities in rapidly industrializing countries could offer the most potential for reducing the emissions of greenhouse gas, as noted in the most recent report from the Intergovernmental Panel on Climate Change.
The problem, the researchers say, is a difficulty in quantifying the energy savings effective policies of planning and urban development might offer on a global scale, since the mitigation potential of urban areas is "insufficiently understood."
"I think one of the central problems is that every city tends to view climate change and energy consumption as their own local problem," says study co-author Felix Creutzig of the Mercator Research Institute on Global Commons and Climate Change in Berlin.
"On the local level, it has been understood but at a global level it is different," he says.
In their survey of 247 cities, which included all of the globe's megacities -- urban sprawls containing in excess of 10 million people -- the researchers were able to profile energy use on a city-by-city basis.
That allowed them to create suggestions of climate mitigation strategies for any urban area based on its particular energy usage characteristics.
A range of factors influence the energy demands of cities, they point out, including population density, transportation infrastructure, technology levels and the price of fuel.
Satisfying the ever-increasing energy demands in the world's growing urban areas while reducing emissions would need a huge commitment to renewable and low-carbon sources of energy, the researchers say.
"As our study shows, cities are indeed very different from each other but we can identify types of cities that are similar to each other (in terms of energy-use,)" Creutzig says.
Climate goals could be easier to achieve with infrastructure that did not require the huge amounts of energy currently being consumed, he says.
"What we are saying is that it would be super-helpful if cities were to develop in an energy efficient way."