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This article is from the In-Depth Report The Future of the Poles

Eyes in the Sky Track Earth's Changes [Slideshow]

Earth-monitoring satellites are being used to track everything from deforestation to the spread of plankton in the Arctic Ocean



Michel de Nijs/ISTOCKPHOTO

Slideshow: View Earth's Changes

In September 2007 less sea ice covered the Arctic than at any point since the U.S. government began keeping records of its decline. All told, it covered 502,000 square miles (1.3 million square kilometers) less ocean than even the year before—a loss equal to an area the size of California and Montana combined. But what might be bad news for polar bears and other animals dependent on sea ice could be good news for the alga known as phytoplankton.

"Because these plants are photosynthetic, it's not surprising to find that as the amount of sea ice cover declined, the amount of [photosynthesis] increased," says biological oceanographer Kevin Arrigo of Stanford University's School of Earth Sciences, who led an effort to use the MODIS (Moderate Resolution Imaging Spectroradiometer) devices on NASA's Terra and Aqua satellites to determine changes in phytoplankton growth.

"If trends continue, we can expect probably a doubling of primary production," in photosynthetic activity undertaken by millions of algae, he adds. Because these organisms are the basis of the food chain, that means more food for fish and, ultimately, the animals that feed on fish (as long as they don't depend on sea ice to do it—like polar bears who use the ice as a hunting platform).

NASA announced this week that this is but one example of the kinds of environmental monitoring that satellites provide. Scientists are also using orbiters to gather information on the gravitational effects of moving glaciers, to determine the impact of drought on the Amazon rainforest, and to generally assess the global impacts of human activity on Earth's ecosystems. Among the findings NASA reported:

  • Soil and water scientist Alfredo Huete of the University of Arizona in Tucson and colleagues determined that old growth in the Amazon actually does better during the dry season. In fact, Huete says, a drought could lead to a relative boom in growth thanks to sunny skies boosting photosynthesis. "Areas that were hit hardest by the drought [in 2005] were actually the greenest and most vigorous," he notes.
  • Satellite surveys of the surface concentration of chlorophyll in the world's oceans show that areas where plankton find it harder to thrive will likely spread as the globe warms, according to biogeochemist Jorge Sarmiento, director of Princeton University's Atmospheric and Oceanic Sciences Program.
  • The relentless march of invasive trees in the canopy of the rainforest on the island of Hawaii—and the changes in the use of nutrients and water they impose—has been mapped with an infrared sensor in aircraft, in research by ecologist Gregory Asner of the Carnegie Institution of Washington's Department of Global Ecology at Stanford University and his colleagues. Putting such sensors on future satellites would enable this type of work to be done anywhere on the planet.

"Over a decade ago, NASA researchers first documented a lengthening growing season," says terrestrial ecology program scientist Diane Wickland of NASA. "We are extending satellite observation records and deriving ever more quantitative information from them."

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