Humans are believed to have destroyed 50 percent of Earth’s wetlands--in California’s Central Valley the figure is 99 percent--by draining swamps to build farms and houses and by harvesting bogs for peat. Wetlands are havens for many species and are also natural wastewater treatment plants.
Researchers this past year estimated that extinctions are occurring between 100 and 1,000 times faster now than they did before humans were around. The rate is greatest in hot spots that contain many endemic species. For example, Hawaii once supported 135 species of land birds that were found nowhere else: 101 are already extinct, and another 24 are rare or threatened.
By burning fossil fuels and using fertilizers, humans introduce more than 300 million tons of nitrogen compounds a year into the biosphere. Besides contributing to acid rain and ozone destruction, nitrogen fallout also overfertilizes some soils--endangering native grasses in American prairies and turning Dutch heaths into shrub lands.
In 1952 the Cuyahoga River made history by catching fire, but these days it and other American rivers and lakes are far cleaner. However, 40 percent of America’s lakes remain unfit for swimming and other uses.
The seasonal ozone hole reemerged over the South Pole last year; in October ozone concentrations there were a third of the historical average for the month and near record lows. While ozone-destroying chlorofluorocarbons have been banned, black-market trade in them may slow the atmosphere’s recovery.
The clash between Spain and Canada over fishing rights off Newfoundland last spring dramatized the global crisis of overfishing. Fish catches from all oceans except the Indian are in decline. New research suggests that fish stocks have not fallen below a fatal threshold, however; if we simply fish less, they will rebound.
Since 1970 the amount of lead added to gasoline worldwide has dropped 75 percent, and people are healthier for it. In the United States, lead concentrations in blood dropped by 78 percent between 1976 and 1994. Other countries lag behind, though; the worst is oil-rich Nigeria, which puts 25 times more lead in its gas than is now permitted in the United States.
Libya consumes 3.7 times its renewable drinking water supply each year by draining underground aquifers. Other desert nations, like Saudi Arabia and Yemen, are also mining fossil water.
It has been estimated that .6 percent of Earth’s rain forests disappear each year, but the numbers are disputed, particularly in the Amazon. Although a recent study puts the loss there at only 6,300 square miles a year--an earlier estimate had it five times as high--Brazil hasn’t analyzed crucial satellite images since 1992. One thing is clear: the fires in Brazil in 1995--deliberately set to clear the land--were the worst ever recorded there.
With the fall of the Soviet Union, ramshackle nuclear reactors are coming to light behind the iron curtain. The U.S. Department of Energy says four facilities in Eastern Europe and Russia, including Chernobyl, are accidents waiting to happen. Worldwide, more than 130,000 tons of spent nuclear fuel are in some kind of storage, a quarter of which is in the United States.
The world’s refugee population has been skyrocketing; it now stands at 23 million, 2 million of whom are Rwandans fleeing their country’s civil war. Rwandan camps in Zaire and Tanzania have been struck by dysentery and cholera, and as the refugees strip the land of vegetation, they threaten already vulnerable species, such as the mountain gorilla. Before the civil war, Rwanda embodied the population crisis rather than the refugee crisis: its fertility rate of 8.5 children per woman was the world’s highest.
While the human population is growing at 1.7 percent a year, many livestock species are swelling at a comparable rate, putting extra pressure on the land. There are 17 billion chickens on Earth--8 billion of them in China--and their numbers are growing by 5.3 percent a year.
Wind power, sometimes noisy but otherwise pollution-free, currently provides only .1 percent of the world’s electricity, but its use is exploding. Developing countries in particular are embracing it: India, for example, has more than tripled its wind-energy capacity in the last two years.
Undisturbed habitats are disappearing all over the world, and nowhere more heartbreakingly than in the Serengeti Plain, home to elephants, lions, giraffes, and other large animals. Conservationists estimate that more than half the Serengeti ecosystem has been disrupted since 1920 by farming, poaching, and other human activities.
Across Russia, Europe, and the eastern United States, forests have been holding steady or even expanding in recent years. In Vermont, forest cover has risen from 35 to 80 percent since 1850. The causes include the abandonment of farms, government protection, and commercial planting. The reestablished forests, though, are often too fragmented to allow the natural fauna to reemerge. And with the fall of the Soviet Union, an explosion of logging may hit Siberian forests.
The CO2 concentration in the atmosphere is now 358 parts per million, higher than it’s been for at least 160,000 years, and 27 percent higher than it was in 1800. The burning of fossil fuels and deforestation release 6 billion tons of carbon a year. While the United States now leads the world with 1.4 billion tons of emissions, China may take first place within a few decades as its growing population burns more coal.
Land degradation by soil erosion, overgrazing, and the like has affected 43 percent of all vegetated land on Earth, according to one 1995 estimate. In Australia, 70 percent of agricultural land has been degraded.