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Paving our way out of greenery

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An environmentalist's protest song laments that we're "using up the world." Two new maps of human environmental impact now make that point graphically.

One shows that the paved parts of the continental United States have grown to cover a total area nearly as large as Ohio and slightly larger than the nation's herbaceous wetlands. The smothering effect of these impermeable surfaces alters watersheds by increasing runoff, reduces the number and diversity of species among fish and aquatic insects, and degrades wetlands, according to Christopher Eldridge and fellow mapmakers at the NOAA National Geophysical Data Center in Boulder, Colo.

Then there's humanity's greedy grab for the lion's share of the land's net primary production - that's the net amount of solar energy captured by plants. It's the basic food source for land-based ecosystems. A research team led by Marc Imhoff at NASA's Goddard Space Flight Center in Greenbelt, Md., estimates that humans now use 14 to 26 percent of that basic resource for food, fiber, firewood, and building materials.

Describing their work in the journal Nature, they call this "a remarkable level of co-option for a species that represents roughly 0.5 percent" of Earth's creatures that depend on that resource. They note that humanity's greed also "alters the composition of the atmosphere, [the] levels of biodiversity, energy flows within foodwebs, and the provision of important ecosystem services" such as clean water and waste disposal.

Dr. Imhoff and colleagues are not the first to point this out. What they have done, with the help of satellite data, is construct the first rough map showing how humanity's preemption of primary production plays out around the world. Hot spots, such as parts of Asia, may claim as much as 70 percent of primary production.


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