Global challenge lies in cities - report
The world faces an urban future, making cities key to global challenges like climate change and poverty alleviation, according to the 2007 State of the World report from the Worldwatch Institute.
Although cities cover only 0.4% of the earth's area they generate almost all of its carbon emissions, the report points out.
Chaotic urbanisation is already taking a huge toll on human health and the environment, especially for the 1bn out of a total of 3bn city dwellers who live in slums with no access to clean water, sanitation or durable housing. The lack of clean water is killing 1.6m urban residents each year.
And as the world's urban population grows each year by around 60m people - a number roughly equivalent to the population of France - the problems are likely to get worse.
"For a child living in a slum, disease and violence are daily threats, while education and health care are often a distant hope," said Molly O'Meara Sheehan, project director of State of the World 2007.
Growing urban areas in Africa are the continent's second greatest challenge after HIV, the Commission for Africa has said.
While currently 35% of Africa's population is urban, the proportion is likely to reach 50% by 2030, the report predicts. "The promise of independence has given way to harsh realities of urban living mainly because too many of us were ill-prepared for our urban future," executive director or UN Habitat Anna Taibaijuka writes in the foreword to the report.
As well as highlighting the risks, State of the World 2007 points to positive action that can prevent the health and environmental damage inflicted by urbanisation.
One example is the Orangi Pilot Project in Karachi, Pakistan, which enabled thousands of locals in low-income households to take charge of bringing good quality sewers to their homes.
Another positive example is a government programme in Rizhao, China, that brought solar water heaters to 99% of households in the city's central districts.
Although there is no escaping an urban future, its negative impacts on health and environment can be warded off. As former governor of Parana in Brazil, Jaime Lerner, writes in the foreword, "a city is a collective dream. To build this dream is vital. It is in our cities that we can make the most progress toward a more peaceful and balanced planet, so we can look at an urban world with optimism instead of fear."