Cities play a vital role in the quest to achieve global ecological sustainability. They are the largest contributors to greenhouse gases and climate change.

However, through sustainable construction and the better use of urban infrastructure, cities could become a critical leverage point in global efforts to drastically reduce emissions and avoid the social and economic costs associated with climate change, as well as enhance energy security and resilience in the face of high fossil energy prices.

This is the key message in a new report by the World Wildlife Fund. It notes, the world's urban centers already account for close to 80 percent of CO2 emissions. In the next three decades, the global population will continue to grow and become ever more urban.

Booz & Company analysis conducted for this report shows that under business-as-usual (BAU) assumptions, US$350 trillion will be spent on urban infrastructure and usage during this period. This huge expenditure either can cause the ecological impact of our cities to become even more pronounced or can be a tremendous opportunity to reduce that impact.

To meet the urban challenge, cities around the world-in developed and developing nations-need to tackle climate change directly. Cities in developed nations can apply new technologies to mitigate greenhouse gas emissions stemming from the usage of their existing infrastructure, says the report.

They can invest in mobility management and incentivize sustainable lifestyle choices.

Cities in developing nations can adopt best practices in urban planning and mobility management, as well as technological advances, to design sustainability into their new infrastructure.

Says the report, cities could become either a force for environmental destruction or a primary source of ecological rejuvenation.

To achieve the latter result, the US$350 trillion to be spent on urban infrastructure and usage over the next 30 years will have to be directed towards low to zero carbon emissions, partic-ularly in the world's small but fastest-growing cities and developing nations, where the largest impacts can be made.

There are three prerequisites for this effort:

• Cities must adopt aggressive energy reduction goals and best-practice approaches to urban planning.
• Innovative financing strategies are needed to provide US$20 trillion to US$30 trillion in funding for additional up-front capital costs, with developed nations working together to assist developing nations in their low-carbonurban infrastructure initiatives.
• The latest technological advances must be utilized to support and enable the planning, construction, and usage of urban infrastructure in all cities.

The report argues if the will can be mustered to aggressively pursue urban sustainability, and these three prerequisites can be put into place, forward-thinking and aspiring urban leaders can generate urgently needed reductions in global emissions, produce attractive economic returns by transforming their cities into centres for ecological innovation, and enhance their energy security.