How Plants May Help Offset Global Warming

Could plants help to slow the march of global warming?

It's possible, suggests a new study, which finds that as climates warm around the world, plants may respond by releasing more aerosol particles into the atmosphere.

The research, published online April 28 in the journal Nature Geoscience, finds that these natural aerosols can fuel cloud formation, which may help cool a warming climate. [The Reality of Climate Change: 10 Myths Busted]

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Aerosols are fine particles of solid or liquid matter, suspended in air. Most of the aerosol particles in Earth's atmosphere come from human activities such as vehicle exhaust, according to the environmental blog The Carbon Brief. Volcanic eruptions also contribute some aerosols to the atmosphere.

But a small percentage of atmospheric aerosols come from living plants, according to a news release from the International Institute for Applied Systems Analysis (IIASA), which co-sponsored the study.

Plants release gases such as water vapor and oxygen; these combine with the aerosols released from plants to form larger airborne particles that reflect sunlight and form cloud droplets.

"Everyone knows the scent of the forest," Ari Asmi, University of Helsinki researcher and co-author of the study, said in a statement. "That scent is made up of these gases."

To measure the cooling effect, researchers collected data from 11 sites around the world, measuring aerosol particle concentrations, plant gases and temperatures.

In warmer temperatures, it was revealed, plants emit more of the gases that stick to aerosol particles. These can lead to cloud formation and, as a result of cloud cover, cooler temperatures.

Other natural phenomenon may help to cool the planet: Some researchers believe that phytoplankton — microscopic plants that drift on ocean currents — may reduce carbon dioxide levels in the atmosphere and lower the atmosphere's temperature.

Other research finds that tropical rainforests, which also absorb massive amounts of carbon dioxide and release water vapor that forms clouds, are critical to stabilizing atmospheric temperatures.

It's unclear how much cooling might actually occur as a result of so-called "biogenic" aerosols.

"This does not save us from climate warming," Pauli Paasonen, lead author of the study, said in the release.

Though in some areas, such as the forests of Finland and Canada, the cooling effect can be as large as 30 percent, the overall global effect is very small, offsetting only about 1 percent of global warming, according to the study.

Nonetheless, the impact of plant-based aerosol formation is an important element in fine-tuning climate forecast models, the researchers believe.

"Aerosol effects on climate are one of the main uncertainties in climate models," Paasonen said in the release. "Understanding this mechanism could help us reduce those uncertainties and make the models better."

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