Plants Help Cool Down the Climate, Aerosol Moderates Weather

Just as the summer comes, it's important to remember that plants release gases to help form clouds and cool the atmosphere, or at least that's what researchers from IIASA and the University of Helsinki believe.

The study identifies a connection between higher temperatures to an increase in concentrations of natural aerosols that have a cooling effect on the atmosphere.

"Plants, by reacting to changes in temperature, also moderate these changes," said IIASA and University of Helsinki researcher Pauli Paasonen, according to a press release.

Some aerosols have been known to cool the climate. However, the effect of so-called biogenic aerosol - particulate matter that originates from plants - had been less well understood. Plants release gases that, after atmospheric oxidation, tend to stick to aerosol particles, growing them into the larger-sized particles that reflect sunlight and also serve as the basis for cloud droplets. The new study showed that as temperatures warm and plants consequently release more of these gases, the concentrations of particles active in cloud formation increase.

"Everyone knows the scent of the forest," said Ari Asmi, University of Helsinki researcher who also worked on the study. "That scent is made up of these gases." While previous research had predicted the feedback effect, until now nobody had been able to prove its existence except for case studies limited to single sites and short time periods. The new study showed that the effect occurs over the long-term in continental size scales.

The effect of enhanced plant gas emissions on climate is small on a global scale - only countering approximately 1 percent of climate warming, as noted in the study.

"This does not save us from climate warming," Paasonen said. "Aerosol effects on climate are one of the main uncertainties in climate models. Understanding this mechanism could help us reduce those uncertainties and make the models better."

The study also showed that the effect was much larger on a regional scale, counteracting possibly up to 30 percent of warming in more rural, forested areas where anthropogenic emissions of aerosols were much lower in comparison to the natural aerosols. That means that especially in places like Finland, Siberia, and Canada this feedback loop may reduce warming substantially.

The results of the study were published in the journal of Nature Geoscience.