The executive director of the United Nations Environment Programme, Dr Klaus Toepfer, says the rich world is not doing enough to make sustainable development a realistic goal for every country.

In a message to mark World Environment Day on 5 June, Dr Toepfer criticises the developed countries, not for their environmental performance, but for giving too little money for Third World development.

Dr Toepfer says: "The fundamental constraint to achieving sustainable development is social inequality and its associated evils: poverty and ignorance".

Only half the developing world have access to drinking water

International development assistance and cooperation, he says, are needed "to manage a host of global issues that respect no borders".

"Unfortunately, the whole level of overseas development assistance is showing a downward trend.

"In 1998 it reached a level of $33 billion, which is 40% lower since the beginning of this decade.

"Seen against the UN target of 0.7% of the gross domestic product of developed countries being spent on development assistance, the present level is nearly $100bn off the target.

"The industrialised world must realise the links between the levels of official development assistance, the debt relief initiatives, and the goals of sustainable urban development, poverty reduction and good governance."

Soaring population

Dr Toepfer paints a sombre picture of the mounting stresses that humanity faces.

Food production needs to double to meet demand

"Over the course of the next decade, approximately 800 million people will be added to the global population.

"Food production will have to nearly double to meet the demands of this growth.

"When this century began, only one in 10 people lived in cities. As we prepare to step into the next millennium, this number will be close to 50% - about 3.2 billion people.

"We started this century with perhaps a dozen cities claiming one million residents or more. By the year 2010, the 20 largest cities in the world will have over 10 million people each.

"Water use is forecast to rise at the rate of 10 to 20% per decade. In developing nations, only half the people have access to safe drinking water.

"As a result of global climate change, phenomena such as the El Nino effect which contributed to catastrophes such as Hurricane Mitch will occur again and again.

"Energy-related carbon dioxide emissions are expected to rise by between 30 and 40% by 2010.

Overcrowded cities are a major problem

"Diseases that thrive in warmer climates are likely to spread due to the expansion of the range of disease-carrying organisms."

And Dr Toepfer warns that some changes brought about by human activity will have irreversible consequences.

"Tropical forests - containing at least two thirds of all plant and animal species - are being destroyed at the rate of 11 million hectares each year.