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Sprawling cities pressure environment
Expanding cities threaten to eat up a swath of land twice the size of New South Wales in less than 20 years, an international conference has heard.

Cities are growing to accommodate a rising global population and as countries like China, India and Brazil pursue fast economic growth.

The world's cities are currently on track to occupy an extra 1.5 million square kilometres by 2030 - equivalent to one-fifth the area of Australia - spelling growing greenhouse gas emissions and resource demand, say experts at the Planet Under Pressure conference in London.

"The way cities have grown since World War II is neither socially or environmentally sustainable and the environmental cost of ongoing urban sprawl is too great to continue," says Dr Karen Seto, associate professor of the urban environment at Yale University.

"The North American suburb has gone global, and car-dependent urban developments are more and more the norm."

Professor Will Steffen, a global change expert from the Australian National University says the most rapid transformations have occurred in the last 50 years.

"Many human activities reached take-off points sometime in the 20th Century and sharply accelerated towards the end of the century. It is the scale and speed of the Great Acceleration that is truly remarkable. This has largely happened within one human lifetime."

The United Nations sees global population rising to 9 billion people by 2050 from 7 billion now, adding around a million people each week.

Most of the growth is expected to come in urban centres with migration from rural areas potentially adding another 1 billion people to cities. That would increase the total urban population to 6.3 billion people by 2050 from around 3.5 billion today.

Steffan warns society may reach a threshold this century.

"Either we turn around a lot of these trends - the carbon dioxide trend, deforestation and so on - or we allow them to continue and push the Earth as a whole across a threshold whereby a lot of these tipping elements are activated and the world moves into a new, much warmer state," he says.
Opportunities

More 70 per cent of current human-induced carbon dioxide emissions already come from cities. Urban emissions are forecast to grow to 36.5 billion metric tonnes by 2030 if no action is taken, from 25 billion in 2010 and 15 billion in 1990.

Urbanisation cannot be stopped, but climate experts argue there is plenty of scope for improving the way cities are planned, developed and run.

"Everything being brought into the city from outside - food, water, products and energy, need to be sourced sustainably. We need to rethink the resource flow to cities," says Sybil Seitzinger, executive director of the international geosphere-biosphere program at the Royal Swedish Academy of Sciences.

New cities offer an opportunity to rethink urban planning while established ones can become more efficient through technology such as time-adjusted toll systems to cut traffic congestion, says Shobhakar Dhakal, executive director of the Tokyo-based Global Carbon Project.

Congestion wastes fuel, time and causes pollution.

It costs world economies an estimated 1 to 3 per cent of gross domestic product and costs New York alone around US$4 billion a year in lost productivity, says experts.

Utility meters and sensors that monitor power generation network capacity and electricity supply and demand can also help conserve energy.

Urban planners can also target more efficient land use, better building standards and policies to promote public transport over car use.

Some cities have made efforts to improve their green credentials, such as Iceland's capital Reykjavik, which depends on geothermal energy and hydro electricity for its energy needs.

Vancouver in Canada sources 90 per cent of its energy from renewable sources like wind, solar and tidal energy and has developed a 100-year sustainability plan.

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