The cynics are already deriding the World Summit on Sustainable Development that opens in Johannesburg at the end of the month. Another expensive gabfest, they complain. But it is important to note that much of this criticism comes from rightwing US politicians who have worked for more than a decade to undermine almost every United Nations initiative.

The subject of the summit is deadly serious. No amount of US hostility should deflect the world from a serious consideration of our environmental future. The right wing seeks to cast doubt on the dangers posed by global climate change, species ex-tinction and ecosystem degradation, presenting such fears as a rehash of old, failed forecasts. Haven't we been warned about the risks of famine, disease and environmental collapse since Malthus's predictions at the end of the 18th century, it asks; and hasn't technology always bailed us out? The answer is complicated.

Technology has indeed averted disaster, but only for those who have access to modern technologies built around first-world science. For a billion or more people in the poorest regions of the world, Malthusian catastrophes are a frequent visitation. Millions every year die prematurely as a result of poverty. Climatic shocks such as this year's drought in southern Africa, delayed monsoons in south Asia and an emerging El Nino cycle put hundreds of millions more at risk.

Moreover, technology does not arrive as manna from heaven. It is the result of significant investment by the public sector as well as the private sector. It was US government-led efforts of the National Institutes of Health, the Centers for Disease Control, the US Department of Agriculture and the universities that contributed indispensably to US food productivity and a string of breakthroughs in medical technology and public health. But these scientific advances have not reached the impoverished peoples of much of tropical sub- Saharan Africa and south Asia, where disease and agronomic conditions are very different. Nor have scientific advances yet resolved the global bind over energy use and climate change.

Free-market fundamentalists are right to deny erroneous claims that we are about to run out of energy on a global scale. The world consumes about 6bn tons of fossil fuels a year worldwide and still has perhaps 10,000bn tons of coal reserves alone, not to mention other fuels.

The problem, of course, is that reliance on coal dramatically exacerbates the risks of man-made climate change. Technological advances here too could bail us out - for example, if the carbon emissions from coal burning could be captured in magnesium ores and stored beneath the earth's surface, as Klaus Lackner, professor of geophysics at Columbia University, has ingeniously suggested. But this too would require considerable research and development from government as well as private sources, and current levels of investment have been tiny.

The other great hope for heading off ecological catastrophe is the slowing of rapid population growth. It took thousands of generations of our species to arrive at the billionth human being in about 1830, but just 170 years more to add an additional 5bn. The sheer momentum created by the current young age structure of the world's population will carry the total up another 2bn or so by mid-century, even if, from now on, every woman were to give birth to just two children. Of course, the world's population is likely to grow faster than this: hundreds of millions of women in the developing world are still having more children than the replacement rate.

Here, again, the US right wing undercuts policies that could promote sustainable development. The attacks on family planning programmes not only threaten 30 years of US efforts but aim to torpedo the invaluable work of the UN as well, by crippling the United Nations Population Fund.

Family planning is not, to be sure, the only policy tool for reducing rapid population growth in poor countries. Extensive experience and research has shown that poor women have fewer children when they are literate, have opportunities for market employment, and have access to health care for their children. High child survival rates give the parents enough confidence to limit the number of children. In this sense, increased education opportunities for girls, expanded healthcare coverage of the world's poor, as well as expanded family planning programmes, should all take centre stage at Johannesburg.

A successful summit in Johannesburg would therefore undertake a number of commitments. The governments would commit to take seriously the challenges of sustainable development - not only for the one-sixth of humanity living with high income but also for the five-sixths of humanity in the developing world - and especially the one-sixth of humanity whose lives are a daily struggle for survival.

They would acknowledge the real risks that population growth and economic activity have generated, ranging from man-made climate change to the depletion of fisheries to the degradation of fragile ecosystems around the world. They would pledge to pay careful attention to the emerging scientific knowledge that is increasingly documenting these risks.

For the poorest of the poor, they would pledge food aid, expanded access to healthcare and family planning services, clean water and sanitation, and a scientific effort to address the problems of tropical disease and agriculture.

And for the world as a whole, they would declare a global effort to mobilise science and technology to ease the harsh trade-off between energy use and climate change so that the still bountiful reserves of fossil fuels could be used safely while other clean technologies are adopted during the century.

All of this the world should do with or without the US at the table, just as it has decided to move forward with the Kyoto Treaty - limiting carbon emissions - despite Washington's arrogant disregard. Sooner or later, the Americans too will wake up to global realities.

The writer is director of the Earth Institute and professor of sustainable development at Columbia University Copyright Financial Times Limited 2002. All Rights Reserved.