Plants help moderate climate warming, says study

According to new research, plants may not be helpless victims as we take our toll on the environment, but instead may actually be helping to moderate the warming of the Earth's climate.

The research, led by University of Helsinki researchers Pauli Paasonen and Ari Asmi, looked at how the production of 'biogenic' aerosols — tiny particles or droplets that float in the air and come from gases emitted by plants — is affected by warming temperatures.

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Scientists are already aware of how aerosols can have a cooling effect on the environment. They can directly reflect sunlight back into space, they can accumulate on other aerosol particles to make them bigger and better able to reflect sunlight back into space, and they can also act as 'seeds' for clouds to form. However, although it was predicted by models, the actual effects of these biogenic aerosols wasn't well known, nor was known how their production was affected by changing temperatures, or how much of an effect they would have on the regional scale or the global scale.

Working with scientists from over a dozen different institutions in Europe, Africa, the United States and Canada, they collected temperatures, aerosol concentrations, plant gas concentrations and measurements of the height of the boundary layer — the layer of air closest to the ground that aerosols mix into, which can change in height from day to day with shifting weather patterns. Taking readings from 11 different sites around the world, they found that plants are reacting to warmer temperatures by producing more of these aerosols, which create more clouds, and thus help to reduce the amount of overall heating.

"Plants, by reacting to changes in temperature, also moderate these changes," said Paasonen, according to Science Daily.

"One of the reasons that this phenomenon was not discovered earlier was because these estimates for boundary layer height are very difficult to do. Only recently have the reanalysis estimates been improved to where they can be taken as representative of reality."

Working with this data, they found that the overall global effect of this is fairly small, only reducing warming by about 1 per cent, but it has a much bigger impact on the regional scale, perhaps up to 30% in rural areas, where these natural aerosols have high concentrations than man-made aerosols. Also, unlike previous studies that only looked at single sites and short time-scales, this new work shows that this can have long-term effects on a much larger scale.

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"This does not save us from climate warming," cautioned Paasonen, according to Science Daily.

Although their study shows that these aerosols from plants can help to cool the planet, the overall effect that plants have on the climate isn't that simple. Plants remove carbon dioxide from the atmosphere, and release water by 'sweating' it out onto their leaves where it can evaporate. This evaporation cools the local environment too, but it's been shown that as carbon dioxide levels increase, it leads to smaller leaf pores and thus less water evaporated into the local air. This may account for the low overall global effect found by this study, however, the true importance of this new work is that it adds to our understanding of how everything in the climate fits together.

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

(Photograph courtesy: Getty Images)

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