Life on Tired Earth

For hundreds of years, cod swarmed in waters off Newfoundland's rugged coast. But by 1992, rampant overfishing had crushed the cod. Price tag to people: tens of thousands of jobs lost and billions of dollars spent in job retraining.

Last year, a weather satellite spotted a monster dust cloud over Africa — hard to miss at 5,000 miles wide. Tree-cutting in northern Africa helps nourish such clouds, which cross the Atlantic, settle into U.S. coastal waters, and possibly contribute to toxic algae blooms. Price tag to people: breathing problems for U.S. coastal residents.

Cod depletion and dust clouds seem like pretty different problems. But they each play a role in the overall environmental degradation of the planet — a condition that a new global study says has escalated so quickly over the past 50 years that it outpaces anything experienced by ecosystems in human history. Demands for water, food, fuel, timber, and fiber — all part of global economic expansion -- have driven the change. The result: a big increase in short-term human benefits, less hunger, and more wealth. But this progress has been counterbalanced by a massive loss of diversity of life on Earth.

That's the state of the world, according to the first Millennium Ecosystem Assessment produced by some 1,300 scientists from 95 countries charged with painting a global eco-portrait. The United Nations-sponsored study was funded by the World Bank and several private foundations.

"We've had many reports on environmental degradation, but for the first time we're now able to draw connections between ecosystem services and human well-being," says Cristian Samper, director of the Smithsonian Institution's National Museum of Natural History in Washington and a chief architect of the study.

Northern Africa's drying Sahel region and Newfoundland's emptier coastal waters, he says, are just two examples in an overall conclusion that 60 percent of the world's ecosystems are being degraded or used unsustainably. Ecosystems being drained or degraded largely in the pursuit of human well-being include:

• Land: More of it has been converted to cropland since 1945 than in the 18th and 19th centuries combined. Cultivated land now covers one-quarter of Earth's land surface.
• Coral reefs: About 20 percent of the world's coral reefs were lost and another 20 percent degraded in the past few decades.
• Rivers and lakes: Despite the fact that the amount of fresh water stored behind dams has quadrupled since 1960, its use for agriculture and other needs has exceeded long-term supplies by 5 to 25 percent.
• Coastal areas: Farmers' increased use of nitrogen fertilizers since 1985 has polluted waterways and coastal ecosystems. About 35 percent of mangrove swamps needed for water filtration in coastal areas have been bulldozed.
• Oceans: Many areas have been overfished, reducing stocks by 90 to 99 percent of preindustrial fishing levels.

"We always have this sense that if we just let up on overfishing for awhile the fish will bounce back," says Tundi Agardy, executive director of Sound Seas, a coastal-planning policy group, who was lead author of the coastal chapter of the millennium assessment. "But what we found is that, many times, the recovery of overexploited species is made impossible by all sorts of things like pollution, habitat loss, and climate change."

The loss of coral, for instance, is often attributed to degraded coastal waters that were harmed over time. Mangrove swamps that filter pollutants were bulldozed for apartment buildings. Combine that with large human populations living seaside and increased agricultural runoff flowing into the oceans. Now add overharvesting of fish that eat algae. Suddenly, you've got algae blooms that overwhelm coral reefs, Dr. Agardy says.