Discovery That Trees Release Aerosols Alters Climate Change Predictions

May 31, 2016 | Joanne Kennell

Tree in a field, clouds
Photo credit: Holly Victoria Norval/flickr (CC by 2.0)

With a little help from the cosmos.

A research group from CERN has unearthed one of the processes behind the formation of small atmospheric particles, also known as aerosols, that could change the way we think about climate change.

Clouds and aerosols — small airborne particles that assist in the formation of clouds — are a necessary ingredient for complete climate prediction models. Why? Because they reflect sunlight away from Earth and back into space. This reflection can have a cooling effect, reducing some of the warming caused by greenhouse gas emissions.

"The best estimate is that about one-third of the warming by greenhouse gas emissions is masked by this aerosol cooling, but the fraction could be as large as half and as little as almost nothing," said Neil Donahue, professor of chemical engineering, engineering and public policy, and chemistry at Carnegie Mellon University, in a press release.

How aerosols form and grow in the atmosphere, as well as how they affect clouds and climate, is the biggest source of uncertainty in human-driven climate change, according to the Intergovernmental Panel on Climate Change (IPCC). It was thought that sulphuric acid, which is produced predominantly from fossil fuel emissions, was required. But according to the new study published in the journal Nature, these aerosols are not just produced as a side effect of pollution — they originate from natural sources too.

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It turns out that these particles can form from a mixture of tree vapors (oxidized molecules) and cosmic rays, which are highly energetic particles from outer space.

"We found that nature produces particles without pollution," Jasper Kirkby, European Organisation for Nuclear Research (CERN) particle physicist and spokesperson of the CLOUD experiment, told Business Insider. "That is going to require a rethink of how human activities have increased aerosols in clouds."

Using CERN’s cloud chamber, scientists recreated Earth’s atmosphere, along with ultraviolet rays at the top of the chamber to simulate sunlight. Then, by directing a beam of artificial cosmic rays from a CERN particle accelerator at the chamber, the team found that the rays affected the rate of aerosol formation. In fact, they found that aerosols formed 10 to 100 times more abundantly if there was an ion from a cosmic ray present.

To estimate how much the planet is going to heat up, scientists look at how warm it will get as carbon dioxide increases from levels before the industrial revolution. But considering that these aerosols naturally exist, albeit likely in smaller numbers, there could have been more white, reflective clouds in the preindustrial era than was previously thought. What this means is that current estimates about Earth’s future warming could be reduced, but only by a little.

"This softens the idea that there may be many more particles in the atmosphere today due to pollution than there were in 1750, and suggests that the pristine pre-industrial climate may have had whiter clouds than presently thought," said Donahue in the release.

But that doesn’t mean humanity is off the hook.

"Human impact is not going to go away," Kirkby said to Business Insider. "Temperature will still go up and warming will still occur. But now that we’ve got this important result that is going to pin down the pre-industrial atmosphere, it’s going to sharpen our results and shrink the range of predictions."

Read next: Tiny Ocean Organisms Play a Surprisingly Big Role in Regulating the Climate

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