CORVALLIS, Ore. - The planet Earth, far more than most people realize, is increasingly dominated by humans in ways that may limit our future prosperity, a group of scientific experts will report Friday in a special section of the journal Science.
That domination far exceeds the agricultural fields, cities or highways where the human presence is most obvious - it affects everything from marine chemistry to obscure species and global climate, said Jane Lubchenco, a distinguished professor of zoology at Oregon State University and co-author of the report.
"When you consider the impact humans have already had on this planet and our dependence upon the goods and services provided by the world's ecosystems, it becomes clear the world is literally in our hands," Lubchenco said. "Even the survival of supposedly wild species and ecosystems will require human involvement."
In this edition of Science, a variety of reports outline different ecosystems and offer policy recommendations for their management. Lubchenco, along with researchers from Stanford University and the U.S. Office of Science and Technology Policy, summarized how profound the human domination already is.
Among their observations:
- One-third to one-half of the land surface of the Earth has been transformed by human activity.
- Two-thirds of marine fisheries are fully exploited, over-exploited or depleted, with millions of tons of non-target animals wasted and the sea floor scarred by dredges and trawlers.
- More than half of all accessible fresh surface water is used by humans, with major rivers such as the Colorado, Nile or Ganges practically drained before they reach the sea.
- The atmospheric carbon dioxide concentration has increased by nearly 30 percent since the beginning of the Industrial Revolution, with major implications for global warming.
- The rate of species extinction is now 100 to 1,000 times more rapid than before human domination, and about one-fourth of all bird species have already been driven to extinction.
No ecosystem on Earth's surface is free of pervasive human influence, the scientists concluded in their report. Although they pointed out there have been some environmental success stories and their summary is "not intended as a litany of environmental disasters," many serious problems are outlined.
The range of human impacts on Earth is vast, the study showed.
Land clearing, urbanization, forestry, grazing, hunting, fishing, industrialization, transportation and international commerce, air pollution, the creation of synthetic chemicals and greenhouse gases all are contributing to major problems, not the least of which is climate change, natural resource depletion and irreversible loss of biological diversity. Impacts range from the deep ocean to the upper atmosphere and every landform in between.
For instance, a recent increase in harmful algal blooms in coastal areas suggests that human activity has affected the base, as well as the top, of the marine food chain, said Lubchenco, who is a marine ecologist. These blooms, which can cause major fish kills or lead to shellfish poisoning in humans, can be correlated to changes in water temperature or nutrient levels - and humans have caused significant increases of nutrients in coastal waters.
There can be ripple effects of human activity, the report suggests. Land transformations can raise carbon dioxide emissions, and the fires associated with land clearing can elevate carbon monoxide levels, causing episodes of urban-like air pollution in remote areas of Africa or South America.
More than 36,000 dams on rivers around the world damage aquatic biological systems, while the global demand for water sucks rivers and ancient groundwater aquifers almost dry.
Human activity is adding as much "fixed" nitrogen to terrestrial ecosystems as do all natural sources combined. This alteration of the natural nitrogen cycle has implications for global warming, acid rain, smog, and nitrate pollution of streams, groundwater and the oceans.
Invading plant and animal species transported by human commerce and other activities can have devastating consequences to native plants, animals and humans. The recent invasion of the zebra mussel in North America is causing billions of dollars in costs for humans, but on a quieter level invading species may be driving other plants and animals to extinction.
"In some areas with heavy commerce, invading species are becoming even more frequent," Lubchenco said. "In San Francisco bay a new species now establishes itself about every three months, as potential invaders are introduced daily in discharge of ballast water."
Lubchenco and the other scientists say that "humans are changing Earth more rapidly than we are understanding it." All of the changes are ongoing, in many cases accelerating, and often entrained long before their importance was recognized. But these seemingly disparate phenomena all trace to a single cause - the growing scale of the human enterprise.
The scientists urged that the rate at which humans alter Earth's systems be reduced by slowing human population growth. They recommended accelerating efforts to understand Earth's ecosystems and how they interact with human-caused global change. And noting that often it's the waste products and by-products of human activity which drives environmental change, they advocated using resources as efficiently as possible.
They also said that humans must accept the inescapable responsibility of actively managing the planet.