In 1999 Time Magazine named Peter Raven a “Hero for the Planet.” It’s a good thing because, as Raven himself tells it, the planet really needs a hero.
Raven, the Engelmann Professor of Botany at Washington University in St. Louis and director of the Missouri Botanical Garden, delivered the Kennedy School of Government’s 2005 Gustav Pollak lecture on March 3. His topic: “Biodiversity and Sustainability: How to Forge the Link.”

Speaking in an energetic, rapid-fire style, Raven sketched in a statistical portrait of a world heedlessly stampeding toward ecological disaster. In 10,000 years, or, to put it in more comprehensible terms, about 400 generations, the human race has gone from 3 or 4 million, living in small scattered bands of hunters and gatherers, to its present population of 6.3 billion and rising.

In the past 50 years alone, the population has more than doubled, while soil erosion has increased by 20 percent, agricultural land has decreased by 20 percent, one-third of the world’s forests have been chopped down, carbon dioxide has increased by one-sixth, and there’s been 7 percent loss of the stratospheric ozone layer.

If the Earth’s carrying capacity were a checking account, we’d be overdrawn. Based on calculations by ecologists William Rees and Hans Wackernagel, it would take 1.2 Earths to support our current population. The fact that we have only one planet at our disposal means that large portions of humanity are undernourished.

Some look to development to correct the problem of unequal distribution, assuming that in time the developing world will reach the standard of living that the developed world already enjoys, but Rees and Wackernagel’s calculations demonstrate the folly of such belief.

“To support everyone at the standard of the developed countries, we would need three Earths,” Raven said. “To support everyone at current standards if the population doubled [a milestone we are likely to reach by the mid-21st century] we would need six Earths. To support double the current population at the standards of the developed countries would take 12 Earths.”

The stress that billions of hungry humans exert on the environment is driving plant and animal species to extinction at a rate unprecedented since Earth’s collision with a giant asteroid wiped out the dinosaurs. Over Earth’s history, the average extinction rate has been 10 species per year, said Raven. But between 1600 and 1950, it has averaged 100 per year. “Currently, we are losing thousands of species every year and soon it will be tens of thousands. At this rate, two-thirds of Earth’s species will be gone by the year 2100.”