By 2030, 1.1 billion more people are expected to be living on Earth—bringing the total to around 8.5 billion.

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In a new report published in the journal, Nature, authors Richard T. T. Forman, a Harvard University research professor, and Jianguo Wu, a distinguished professor of sustainability science at Arizona State University, said urban expansion alters a city's 'big seven': natural vegetation, agricultural land, clean water, jobs, housing, transport and communities.

Moving forward, the authors argue we need worldwide cooperation on a new approach to planning cities that will house all of these new people and stop our increasingly heavy ecological footprint.

"It will require international and national policies for environmental protection, urban development and human migration. And each city must develop an urban regional plan," the authors wrote.

Aa far as where people can go, Forman and Wu said they see promise in large areas in the Americas, central Africa and Asia as well as pockets of Oceania due to its warm and moist climates suitable for growing crops such as cacao, coffee, palm oil, rice and corn.

They also said metropolitan regions should encourage and develop compact communities—like ones found outside Portland, Oregon, and Canberra, Australia—which provide space for sustainable communities and limits the loss of valuable land.

"Local officials and decision-makers will need policies and incentives to encourage sustainable development in these zones, particularly in rural villages, which tend to empty out as residents move to cities for work," the authors said.

The idea and execution of city planning, they said, should be reversed to focus on building structures around valuable natural resources, not on top of them.

"Society must think globally, plan regionally, then act locally," the authors concluded.

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