Cities damage Earth more than population increase

It is not the total number of people on the Earth but the number of homes they live in that poses the greatest threat to the Earth. More homes mean bigger cities and bigger cities mean unbridled consumption.

Several views of how humans are damaging the Earth were presented at the American Association for the Advancement of Science meeting in San Francisco. Many of the studies did not depend on the familiar greenhouse gas assumptions but on how we are transforming the Earth's surface.

"Since 1850 there have been 10.7 million square kilometres converted to urban and agricultural use," stated Prof Emilio Moran of Indiana University. He dismissed as "myths" claims that urbanisation had little impact because cities only represent about 2 per cent of the Earth's surface. It is assumed that population growth is the driver behind climate change but he believes that the growth of city living is the key.

"In fact when you examine the data in the field . . . it is not the number of people - it is land use. It is not the number of people, it is the number of households." About 75 per cent of people in Latin America live in urban areas. Even in the remote Amazon basin 60 per cent live in cities and towns.

"Urban populations have a higher consumption pattern of behaviour that leads to rising demand for food and fibre. Land cover change is increasingly a result of urban decisions," Prof Moran said. This greater consumption level means more climate change.

Prof Lonnie Thompson, of Ohio State University, provided dramatic evidence of how climate change is altering the Earth. The famous white ice cap sitting on Tanzania's Mount Kilimanjaro will be gone in 15 years and nothing can be done to stop it.

A third of Kilimanjaro's massive ice field has melted away over the last dozen years, he said. What remains is just 20 per cent of what was recorded in the first mapping of the ice field in 1912.

A similar picture emerges in Peru's southern Andes. There have been eight measurements of the ice cap on Quelccaya. Between 1963 and 1978 the ice was vanishing at an annual rate of 4.7 metres. The rate over the last three years, however, has been an astonishing 155 metres a year, Prof Thompson said.