The Why Files The Why Files --

Earth Day 2006: Checkup reveals global fever


How healthy is Mother Earth?
It's only fitting that Mother Earth get a day to herself. The rest of the year, we go on tilling, mining, logging, burning, burying trash, and otherwise taking advantage of Mother.A small marine snail with brown internal organs seen through a clear body.

We act like we have a spare (and livable) planet waiting in the wings.

Once in a dozen moons, it makes sense to think about your Mother. How's her health? Is she getting forgetful?

What about her fever?

The shells of these pteropods started to erode after 48 hours in acidic ocean water. Will burning fossil fuels disrupt the oceanic food chain? Photo: NOAA

We've been hearing about global warming for 25 years, and the bad news just won't quit. To assess the state of the scientific art, The Why Files attended a session on global change at the latest American Association for the Advancement of Science (AAAS) meeting in St. Louis.

After hearing about melting ice, rising sea levels, and the global consequences of deforestation, we came away alarmed about Mother's health.

Brown, antler-shaped coral in clear blue sea.
Carbon dioxide absorbed in the ocean is turning the sea acidic. That could further harm corals that are already stressed by warming oceans and pollution. Healthy elkhorn coral in Bonaire, Netherlands Antilles (Caribbean Sea), courtesy Gordon Medaris

Ocean turning sour
As we humans continue burning ever greater amounts of fossil fuel, rising levels of carbon dioxide are heating the atmosphere through the greenhouse effect. About half of human-produced carbon dioxide leaves the atmosphere and gets absorbed in the ocean.

That's a good thing, since it moderates the increase in greenhouse gas. But too much of a good thing is a bad thing. When carbon dioxide dissolves in seawater, the water becomes more acidic, which reduces the concentration of carbonate ion -- CO3-2. "The rapid increase in atmospheric CO2 will inevitably and predictably increase ocean acidity, and change carbonate chemistry," Katherine Richardson of the University of Aarhus (Denmark) told AAAS.

And how will rising ocean acidity affect the shelled animals that build their "homes" (okay, we meant to say shells...) with calcium carbonate? This group includes coral, and countless small, free-floating, calcified animals that occupy the bottom of many oceanic food chains.

One of those critters is the pteropod. These guys don't get much press, but in some Antarctic waters, pteropods are even more common than the krill that support baleen whales, Richardson said. And it just so happens that carbonate concentration is already low in the Southern Ocean, so any further reduction could harm pteropods.

 Many sea creatures of different colors, shapes and sizes crowd together on ocean floor.
Calcium carbonate is the basis for shells of the planktonic foraminifera (the popcorny white items), bryozoa stalks, pteropods (the clear snail-like shells) and sponge spicules (the 3-pronged specimens). Photo: NOAA

Shell game
James Orr, of the laboratory for climatic and environmental science at the French National Center for Scientific Research, dunked pteropods in ocean water that had low concentrations of aragonite, a form of calcium carbonate. Within 48 hours, the shells were damaged. If other pteropods living near Antarctica respond in the same way, "We hypothesize that these pteropods will not be able to adapt quickly enough to live in the undersaturated conditions," Orr wrote with his collaborators (see "Anthropogenic Ocean..." in the bibliography)

If you eat fish or care about global biodiversity, this could be bad news, even if you don't know a pteropod from a pterosaur. It's the food chain, stupid. "If pteropods are excluded from polar and subpolar regions, their predators will be affected immediately," Orr wrote, and the problem could echo up the food chain to cramp the supply of beautiful or tasty animals like North Pacific salmon, mackerel, herring, cod and baleen whales.

The pteropod die-off could happen within 50 years, Orr wrote. And in another 50 to 100 years, the shells of surface-dwelling plankton like foraminifera and coccolithophorids could start dissolving as well.

"Global change is more than climate change," Richardson says. Vast ocean ecosystems "will be changed dramatically if it is not possible for these organisms to survive. It's one more reason to be concerned about rising concentrations of CO2. Very often scientists say we should not play god, but if we don't do anything, we will end up in situation where we are inadvertently playing god."

Graph documents the stead rise of carbon dioxide in our atmosphere In terms of carbon dioxide in the atmosphere, she concluded, "We are in a place we haven't been in the last 500 million years."

Since 1959, the steady rise in carbon dioxide concentration has been measured on a mountaintop in Hawaii. Annual fluctuations in the summer show when plants are respiring carbon dioxide. Graph: NOAA

Certainly, the atmospheric concentration of CO2, now 382 parts per million, is higher than it has been for at least 650,000 years. Last fall, an ice-coring project in Antarctica reported that air trapped in the ice always contained less than 300 parts per million of carbon dioxide. The researchers also saw a "rather stable coupling between climate and the carbon cycle" in their ice cores (see "Stable Carbon..." in the bibliography). Translated: when carbon dioxide rose, so did global temperature.

Live near a coast? You need to read about massive melting.


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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