THE National Academy of Sciences in the United States and the Royal Society in Britain recently issued a joint statement of warning to the world.
The presidents of these normally reserved institutions put the matter bluntly: "World population is growing at the unprecedented rate of almost 100 million people every year, and human activities are producing major changes in the global environment.
If current predictions of population growth prove accurate and patterns of human activity on the planet remain unchanged, science and technology may not be able to prevent either irreversible degradation of the environment or continued poverty for much of the world."
Some would argue this is another hyped-up alarm by environmentalist zealots. After all, fertility rates - the numbers of children per woman - are declining in most of the developing world, as they have for years in industrialized countries.
But if fertility rates don't decline much more quickly in coming years, world population could still end up many times its current 5.4 billion by the middle of the 21st century. For many countries, that portends social and environmental upheaval.
So the warning, though it may sound familiar themes, remains timely. Specifically, the National Academy of Science and Royal Society hope to encourage discussion of the population issue at the United Nations Conference on Environment and Development in Brazil this June.
Their statement also throws some national political issues into a new perspective.
For example, Earth's productivity, including agriculture, depends on maintaining a healthy biodiversity. Yet species of organisms ranging from higher plants and animals to microbes are disappearing at an alarming rate. Controversies like that surrounding the spotted owl in the Western US ought to be seen in this, as well as other, contexts.
Likewise, issues of energy efficiency or materials recycling aren't just matters of self-sufficiency or local pollution control. They are tied to the global need to ease the environmentally destructive exploitation of primary resources.
What may be most important, the restriction of US foreign aid for family planning, to please a small constituency hostile to birth control, is a disservice to all humanity. The joint statement notes:
"By providing people with the means to control their own fertility, family planning programs have major possibilities to reduce rates of population growth and hence to arrest environmental degradation."
Earth's environmental challenge involves an interlinked mix of population stress, unwise resource use, and economic backwardness for the bulk of humanity.
The scientists' warning doesn't dismiss the progress being made in addressing these problems. It correctly stresses that this is no time to let up.