The combined forces of population growth and urbanization are creating a planet of slums, where the urban population will have doubled by 2030, according to a report released by the United Nations today.
The shanty towns that choke the cities of Africa and Asia are experiencing unstoppable growth, expanding by more than a million people every week, according to the "state of the world's population" report.
The UN's findings echo recent predictions that 2008 will see a watershed in human history as the balance of the world's population tips from rural to urban. Many of the new urbanites will be poor and the shelters into which they move, or are born, will be slums.
"The growth of cities will be the single largest influence on development in the 21st century," the report states. It maintains that over the next 30 years, the population of African and Asian cities will double, adding 1.7 billion people - more than the current populations of the US and China combined.
In this new world the majority of the urban poor will be under 25, unemployed and vulnerable to fundamentalism, Christian and Islamic.
Mike Davis, a population expert, described this emerging underclass in his recent work Planet of Slums as: "A billion-strong global proletariat ejected from the formal economy, with Islam and Pentecostalism as songs for the dispossessed."
While some critics have accused Mr Davis of scaremongering, the UN's findings appear to back many of his basic assertions.
George Martine, a demographer and the author of today's report, said: "The urbanization is jolting mentalities and subjecting them to new influences. This is a historical situation. And now one of the ways for people to reorganize themselves in this urban world is to associate themselves with new or strong, fundamentalist religion."
The rise of radical Islam in Africa, from the outskirts of Jakarta to the slums of Egypt, is well documented but the continent is also experiencing a Christian shift, with Pentecostalism winning converts from Uganda to the Democratic Republic of Congo.
In Latin America, identified by the UN as the other engine of urban growth, the once all-encompassing Catholic Church is battling for hearts and minds with radical evangelical churches. This battle was one of the key points of Pope Benedict XVI's recent trip to the world's most populous Catholic country, Brazil.
Urbanization is inevitable, the report warns, and calls on planners to accept that the poor have the right to a place in the city. It argues that this influx can be positive if properly managed. No country in the industrial age has enjoyed economic growth without urbanization.
"It's pointless trying to control urban growth by stopping migration," Mr Martine said. "It doesn't work. We have to change mindsets and take a different stance. We're at a crossroads and can still make decisions which will make cities sustainable. If we don't make the right decisions the result will be chaos."
UN-Habitat uses the term "slum household" to describe a group of individuals living under the same roof in an urban area who lack one or more of the following: durable housing, sufficient living area, secure tenure and access to clean water and sanitation.
Until now the response of national and municipal governments to ballooning growth has been to discourage newcomers but this is a failed policy, the report argues. "It has resulted in less housing for the poor and increased slum growth," the reports says. "It also limits opportunities for the urban poor to improve their lives and to contribute fully to their communities and neighborhoods."
Mr Martine argues for a more positive approach to urbanization, saying that by providing land for housing with at least some services and planning in advance to promote sustainability, progress can be achieved.
Slums have been part of human communities since Mesopotamia but our modern concept of segregated slums for the poor comes from the Industrial Revolution. The difference between then and now is a question of scale, with today's slum dwellers being one-in-three of all city dwellers.
More than 90 per cent of this underclass are in the developing world, with South Asia having the largest share, followed by eastern Asia, sub-Saharan Africa and Latin America. In sub-Saharan Africa, growth has become synonymous with slums and 72 per cent of the population live in slum conditions.
Growth of urbanization
* By 2008, more than half of the world's current 6.7 billion population will live in cities.
* By 2030, the urban population will have risen to 5 billion, 60 per cent of the world's population.
* Half of the world's urban population is currently under 25. By 2030, young people will make up the vast majority of the 5 billion urban dwellers.
* Between 2000 and 2030, Asia's urban population will increase from 1.3 billion to 2.64 billion. Africa's population will rise from 294 million to 742 million, Latin America and the Caribbean from 394 million to 609 million.
* Mega-cities do not have a monopoly on population growth. More than half of the urban world lives in cities with a population of less than 500,000.
© 2007 The Independent