By Sara Sreberny-Mohammadi
BBC News Online in Barcelona
World leaders and mayors have warned that rapid urbanisation is set to become one of the biggest challenges facing humanity in the 21st Century.
Two-thirds of the world's population will live in cities by 2050
Already 50% of the world's population live in an urban setting and that could grow to two-thirds by 2050, the World Urban Forum in Barcelona was told.
"Urbanisation is bringing problems of concern to us all," said Mikhail Gorbachev, the former President of the USSR and the current chair of Green Cross International.
"Four years ago, when world leaders adopted the Millennium Declaration, it seemed they recognised the urgency of the problems," he added.
"But all of us today are concerned that many leaders, having taken that step, have not shown the political will to implement them and the obligations they assumed."
Others at the Forum have been quick to express concern that millions of the world's urban inhabitants still lack access to safe water and sanitation, health care, education and security.
They believe current trends may make it difficult to meet the Millennium Development Goals (MDGs), agreed by the UN in 2000, and which aim to halve world poverty within 20 years.
The MDGs cover hunger, disease, illiteracy, environmental damage, and halting the spread of HIV/Aids.
Searching for a strategy
UN-Habitat's executive-director, Mrs Anna Tibaijuka, noted that the world had still to produce an effective strategy to make cities work for everyone.
Meanwhile the chair of the World Urban Forum - Spain's minister of housing, Maria Antonia Trujillo - stated that urban poverty was particularly acute in the developing world.
And on current trends, the situation was unlikely to improve, she said.
In the developing world, the majority of future city dwellers will be living in abject poverty - in slums and settlements without access to basic human needs, such as shelter, water and sanitation.
To help develop local administrative independence globally, a worldwide Barcelona-based body, United Cities and Local Governments (UCLG), was formed in January 2004.
Citing a European Union treaty providing local authorities with necessary independence, Mr Joan Clos, the Mayor of Barcelona, said UCLG now sought an international treaty recognised by the UN.
The Dutch housing and environment minister, Pieter van Geel, argued that urban poverty was no longer affecting only cities. He said rapid urban expansion was putting more pressure on rural areas, too.
He cited problems associated with increased deforestation and flooding.
The World Urban Forum has so far brought together over 3,000 people, including several world leaders and over 600 mayors from across the globe.