So Small!

Size really does matter when it comes to global climate

They are so small, you'd think they would hardly count, but single-celled plants that float in all the world's oceans could provide a key to understanding and, perhaps, even controlling the earth's climate.
Robert Frouin and Sam Iacobellis of the Scripps Institution of Oceanography at the University of California, San Diego, have discovered that microscopic phytoplankton, which cover about three-quarters of the earth's surface, help keep our planet warm. They believe the findings have important implications for predicting climate change because the effect of phytoplankton has been largely ignored until now.
The ecological, but not the climatic, importance of phytoplankton has been known for some time. The biggest role of these tiny organisms is in providing the main source of food for animal life throughout the oceans. However, the effect their presence has on the climate has not been looked at experimentally. The Scripps team has now used satellite images from the "Coastal Zone Color Scanner" to show that phytoplankton absorb heat from the sun that would otherwise be bounced back into space. The result is that oceans teeming with phytoplankton are between 0.1 to 0.6 degrees warmer than they would otherwise be, and that's no drop in the ocean in climate terms.
These minute and free-floating plants could have an even greater impact than warming the oceans by half a degree or so. Changes in solar reflection from the Earth's caused by increases or decreases in phytoplankton concentrations may significantly affect the way greenhouse gases released by human activity affect the planet's climate system. Frouin and Iacobellis argue that phytoplankton exert "a significant and previously uncalculated influence" on the Earth's climate.
In May 2001, Frouin and Iacobellis published a related study that showed how whitecaps - the frothy tops of waves, could influence climate by reflecting solar radiation from the Earth's surface. The effect of phytoplankton, they have found, is ten times greater than this. If there were no phytoplankton our climate would be cooler. "The effect of phytoplankton is about 20% of the combined radiative forcing due to increased greenhouse gases and anthropogenic aerosols since pre-industrial times," Iacobellis told us. This, adds Frouin, is a problem that has to be looked at more carefully if scientists are to make more accurate predictions of climate change.
This new research will help climatologists build better predictive models of global climate change. Better models mean far-sighted policy decisions can be made on a firmer basis. The research could, for instance, persuade policy makers of the folly of "fertilising" the oceans with iron to increase phytoplankton growth.
Several scientists have suggested that iron fertilisation could be one way to reduce global warming by increasing the amount of the greenhouse gas carbon dioxide absorbed by the photosynthesising phytoplankton. Frouin points out that this might not go according to plan. "We are saying that if you increase the amount of phytoplankton in the ocean, which would probably be a consequence of this iron fertilization, you would contribute to warming the ocean because there would be more phytoplankton absorbing more radiation rather than cooling the planet by absorbing the carbon dioxide."
There is yet another complication. Some species of phytoplankton reflect the sun's radiation rather than absorb it, so more of them might have a cooling effect. "This just shows how intricate the climate system is," adds Iacobellis. "It's like a ball of yarn all pushed together. It's difficult to unpiece the climate or put together what might happen in the future when all these things act together. One by itself may not be that important but when thousands of these small things act together, then?"

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