Thin the Air, Save the Biosphere?

1 June 2009 (All day)

Someday solution. Fiddling with atmospheric pressure may be one way to prevent a future apocalypse.

Sometime between 100 million and 1 billion years from now, Earth will have lost so much carbon dioxide from its atmosphere that plants and trees will literally begin suffocating, eventually taking all life with them. In a new study, researchers propose one way to delay this Armageddon: reduce the pressure of the atmosphere, effectively creating conditions where we all feel like we're living at high altitudes.

Over the geologic history of Earth, CO2 levels in the atmosphere have been dropping. Today, concentrations are only a small fraction of what they were several billion years ago. Plants, algae, and other photosynthesizers consume CO2, but much of it is eventually returned to the atmosphere when the organisms die. So some other process must be socking away CO2 permanently. The available chemical evidence points to the action of silicates in rocks: The compounds somehow turn carbon into bicarbonate and pull it out of the biosphere. If the trend continues, researchers have found, Earth would not be able to sustain photosynthesis for more than about a billion years.

A team from the California Institute of Technology in Pasadena led by physicist King-Fai Li wondered if there was any way to stop this potential catastrophe. The researchers created models of Earth's atmosphere over the next several billion years. When they factored in a constant level of CO2, they discovered a surprising development: The change required a lower overall atmospheric pressure--about one-sixth today's pressure at sea level. With that change, Earth's biosphere could persist for an extra 1.3 billion years, the team reports online today in the Proceedings of the National Academy of Sciences. The reduction in atmospheric pressure would counteract the complex interaction of the CO2 and the nitrogen in the atmosphere with seawater and the rocks on the ocean bottom; the net effect would be less permanent sequestering of carbon and a longer lifetime for photosynthesis, the team reports. "This is the first study that makes use of the idea that atmospheric pressure could have varied over Earth's history," Li says. "And it shows how that variation could continue to affect the atmosphere."

The trick to achieving this reduction of pressure, the researchers say, would be to develop a technology that sucks nitrogen from the air, which at 78% constitutes the bulk of Earth's atmosphere. The downside would be thinner air, though because of other factors oxygen would be enriched. This would require our distant descendants to develop the same physiology as the Sherpa people of Nepal, who can live comfortably at elevations that make most other people either ill or in danger of dying. Still, the conditions could give our distant descendants some extra breathing room, Armageddon-wise.

Global ecologist Kenneth Caldeira of the Carnegie Institution in Stanford, California, who has studied the implications of low carbon concentrations in the atmosphere, says the researchers have made "a persuasive case" that pressure can play an important role in the planet's long-term atmospheric composition. But Caldeira says he doubts that anyone knows what will happen to total atmospheric pressure in the distant future.

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View the Proceedings of the National Academy of Sciences report