Urban planners and municipal authorities around the world are striving to transform their cities into paragons of sustainability.
As climate change becomes an increasingly pressing issue, environmental experts and city planners are sounding a clarion call for the incorporation of more sustainability measures into the design and development of modern urban centres.
Stephanie Pincetl, director of the California Center for Sustainable Communities at UCLA, says that if cities can be likened to living organisms, then "urban metabolism" is a highly useful concept for assessing their efficiency and lifting their sustainability levels.
"Urban metabolism is an analogy...[which] provides useful insights for policy makers and others to target energy efficiency and conservation programs," Pincetl said.
The concept of urban metabolism lies at the very heart of one of the latest and most prominent manifestos advocating greater sustainability in cities.
Sustainable Urban Metabolism by MIT academics Paulo Ferrao and John Fernandez asserts that an increase in the sustainability of cities is nothing short of a necessity in the 21st century, especially given the sharp rise in urbanization rates in emerging economies.
"The world needs to make a shift to become more sustainable," said Ferrao, a mechanical engineer by training who is now the director of the MIT-Portugal Program. "Cities are really the engines of growth, so whatever is going to happen in the world will happen in cities, particularly consumption of material resources."
Municipal authorities and city planners around the globe are now heeding the call from Ferrao and others for increased sustainability in an urban setting.
The north German port city of Hamburg, which won the coveted title of European Green Capital in 2011, is a sterling example of successful efforts by municipal government to shore up efficiency.
Measures adopted by Hamburg to raise its sustainability levels include the expansion of public transportation, with the construction of a new light rail system which is scheduled to open in 2014, and an increase in cycling infrastructure in tandem with the launch of a city-wide bike rental system.
With respect to energy supply, Hamburg is now in the process of more than doubling its wind turbine installations from 45 megawatts to 100 megawatts, while municipal power company Hamburg Energie added a further 10 megawatts of solar power to the city's roofs in 2011 alone.
Urban housing in Hamburg focuses on passive homes which do not employ conventional high-energy heating systems. Environmental protection requirements also mandate that all public buildings be based on this passive house standard.
The Hamburg Senate hopes this raft of measures will serve to reduce the city's carbon dioxide emissions by 40 per cent by 2020, and by 80 per cent by mid-century, compared to benchmark levels in 1990.
Efforts to improve urban sustainability are far from confined to the first world, however. If anything, the need for sustainable cities is even more acute in developing economies, the growth of which are often reliant on pollution-heavy industries.
The Chinese government has made sustainability an integral part of its long-term development strategy with ambitious targets for low carbon usage, energy efficiency and clean technology incorporated into its 12th Five Year Plan.
The creation of "eco-cities" in China embodies Beijing's ambitions with respect to sustainable urban development.
The Tianjin Eco-City, a collaborative project between the Chinese and Singaporean Governments, boasts a plethora of cutting-edge green features, including integrated waste management, the adoption of a light rail transit system as the primary mode of transportation and the use of desalinated water for nature strips.
The location of the Tianjin Eco-city is highly pertinent, situated in the northeastern port city of Tianjin, just adjacent to the capital of Beijing and Hebei province, which suffers from some of the worst air pollution in the country.
Following the remarkable example set by the Tianjin Eco-city, another similar project is currently under development in the vast inland province of Sichuan.
The "Great City" project is situated just outside the Sichuan capital of Chengdu, and will entail the construction of a complete urban centre from scratch, covering over 7 million square metres and serving as host to a population of around 80,000.
Planners hope the new eco-city will be a paragon of sustainability, relying upon clean sources of energy, minimizing waste production, and featuring a public transportation system which will render the use of private vehicles unnecessary.