Paving our way out of greenery

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.

The bottom line is that humans can't go on living this way. We consume too much of the planet's primary biological resources to maintain a healthy environment. The consumption map will help local and regional authorities see their local resource planning in a larger context.

You can say the same for the paving map. As Dr. Eldridge and his colleagues note in publishing their map in the journal Eos, this is the first time that satellite and ground-based data have been used to put local impacts in a national context. The loss of permeable land to roads, parking lots, buildings, airports, and swimming pools can no longer be considered just a local concern. We need a similar map for the entire globe.

The pace of turning land into impermeable surface is faster than you might think. The research team reports that in the US "public and private sector construction spending tops $480 billion per year. This includes more than one million new single-family homes and in excess of 10,000 miles of new roads per year."

The ultimate driving force behind such impacts is population growth. The Goddard team notes that the US is adding 3 million people a year. A recent UN report warns that the world is turning fertile land into desert at a rate that now puts a third of the land surface at risk. Again it blames population growth along with poor land-use practices.

New tools to aid planners, such as the maps reported here, can help correct poor practice. But only facing the population crunch squarely and curbing its unhealthy growth will cure the underlying reason that we are "using up the world."

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