Tree detection messes with climate calculations

Zoom in / The early morning sun shines through morning fog in rural Chongqing, China, September 14, 2023.

Every year between September and December, Lubna Dada creates clouds. Dada, an atmospheric scientist, gathers with dozens of colleagues to conduct experiments in a 7,000-gallon stainless steel chamber at CERN in Switzerland. “It’s like science camp,” says Dada, who studies how natural emissions interact with ozone to create aerosols that affect the climate.

Clouds are the biggest source suspicion In climate predictions. Depending on the location, it could be cloud cover Reflect sunlight away of land and oceans that would absorb its heat, a rare feature in a warming world. But it can also be withdrawn trap Heat above the ice in the Arctic and Antarctica. Scientists want to know more about what causes clouds to form, and whether this effect is cooling or heating. Most of all, Dada says, “we want to know how we humans changed clouds.”

In the sky, aerosol particles attract water vapor or ice. When the little wet balls get big enough, they become… Cloud seeds. Half of Earth’s cloud cover is made up around things like sand, salt, soot, smoke, and dust. The other half is formed around vapors released by living organisms or machines, e.g Sulfur dioxide, which arises from burning fossil fuels.

At CERN, scientists repeat this process by injecting the steel chamber with vapors representing specific environments. (It’s called a cloud chamber, after the cosmic droplets left outdoors.) For example, it could simulate the gases found above cities. But Dada, who usually works at the Paul Scherrer Institute in Switzerland, went to the European Organization for Nuclear Research (CERN) to look into the past. Her team of scientists from around the world wanted to recreate the air above forests, because a “pure” atmosphere refers to what cloud formation was like before industrialization. “We need this comparison to a time when there were no human emissions, so we can fix our climate models,” she says.

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In a published paper This month In Science Advances, Dada’s team has created a powerful new factor in cloud formation: a type of chemical released by trees. Trees emit Natural volatiles Such as isoprene and monoterpenes, which can spark Cloud formation Chemical reactions. Dada’s new work focuses on a neglected class of less abundant volatiles called sesquiterpenes, which have a woody, earthy, acidic or spicy scent, depending on the molecule and the type of plant or microbe emitting them.

The team shows that sesquiterpenes are more effective than expected at seeding clouds. Just a 1 to 50 ratio of sesquiterpenes to other volatiles Doubled Cloud formation.

The role that trees play in seeding clouds is important, because it suggests what the sky might look like over some areas if governments could limit sulfur emissions. In a world with less pollution, plants and trees will become the most dominant driver of cloud formation, an echo of the pre-modern world.

This research could help improve estimates of what the atmosphere was like before industrialization. We may have underestimated the number of aerosols in the world by overlooking a large portion of those that come from trees. If so, climate models will need to be retooled.

“The formation of new particles is a very hot topic right now,” says Paquita Zuidema, an atmospheric scientist at the University of Miami, who was not part of the study. “We’re starting to realize more and more that we don’t know exactly what pure weather looks like.”

While anthropogenic emissions dominate cloud formation in populated areas, plant volatiles dominate pristine lands elsewhere. Laboratory tools have recently become sensitive enough to understand which ones contribute the most.

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Many discoveries about sesquiterpenes are relatively recent. In 2010, Researchers discovered them Near the Amazon forest floor. High up in the canopy, sesquiterpenes were difficult to track. This suggests that ozone was converting sesquiterpenes into cloud-feeding aerosols. Dada reported a similar system in Finnish forests and peatlands last year. “We’re seeing more and more because our tools are so much better now,” she says. “They’re not just in the Amazon.”

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