Lubna Dada creates clouds from September to December every year. Dada, an atmospheric scientist, has gathered with dozens of colleagues to conduct experiments in a 7,000-gallon stainless steel chamber at CERN in Switzerland. “It’s like a science camp,” Dada said. He studies how natural emissions react with ozone to produce aerosols that affect the climate.
Clouds are the biggest source uncertainty In climate prediction. Depending on the location, it may be cloudy. reflect sunlight away Heat sources from land and sea that would otherwise absorb heat. This is a rare perk in a warming world. But clouds can also do things like: trap Heat on the ice of the Arctic and Antarctic. Scientists want to learn more about what causes clouds to form and whether the effect is cooling or heating. More than anything, Dada says, “I want to understand how we humans have changed the clouds.”
In the sky, aerosol particles attract water vapor and ice. When the small wet mass becomes large enough, cloud seeds. Half of Earth’s clouds are formed around things like sand, salt, soot, smoke, and dust. The other half nucleates around vapors emitted by organisms and machines. Sulfur dioxide produced when burning fossil fuels.
At CERN, scientists recreate the process by injecting steam representing a particular environment into a steel chamber. (This is called a cloud chamber, in the sense of space that leaves droplets outdoors.) For example, it can mimic the gases found in the sky above a city. But Dada, who normally works at the Paul Scherrer Institute in Switzerland, went to CERN to peer into the past. Her team of scientists from around the world wanted to recreate the air above a forest. That’s because a “pristine” atmosphere suggests what cloud formation was like before industrialization. “To revise climate models, we need to compare them to a time when there were no human emissions,” she says.
Among the published papers this month In Science Advances, Dada’s team established a new dominant player in cloud formation: a type of chemical emitted by trees.trees emanate natural volatiles Potentially flammable, such as isoprene and monoterpenes cloud formation Chemical reaction. Dada’s new book focuses on an often overlooked class of volatile substances called sesquiterpenes, which can be used to smell woody, earthy scents, depending on the molecule and type of plant or microorganism that releases them. scent, citrus, or spicy.
The research team showed that sesquiterpenes were more effective than expected in cloud seeding. The ratio of sesquiterpenes to other volatiles is only 1:50 doubled cloud formation.
The role of trees in seeding clouds is important because it suggests what the skies above some regions might look like if governments were able to curb sulfur emissions. In a world with reduced pollution, plants and trees will become more dominant drivers of cloud formation. This is an echo of the pre-modern world.
This research could help improve estimates of what the pre-industrial atmosphere was like. Perhaps we have overlooked a large portion of aerosols generated by trees and have underestimated the world’s aerosol population. If so, climate models will need to be rebuilt.
“The formation of new particles is a pretty hot topic right now,” says Paquita Zuidema, an atmospheric scientist at the University of Miami who was not involved in the study. “We’re becoming increasingly aware that we don’t know exactly what a pristine atmosphere looks like.”
Anthropogenic emissions dominate cloud formation in populated areas, whereas elsewhere plant volatiles dominate in more natural lands. Lab tools have recently become sensitive enough to understand which tools contribute the most.
Many discoveries regarding sesquiterpenes are relatively recent. In 2010, researchers discovered them Near the Amazon forest floor. Higher in the tree canopy, sesquiterpenes were difficult to track. This suggests that ozone converts sesquiterpenes into aerosols that seed clouds. Dada reported a similar system. Finnish forests and peatlands last year. “We’re seeing more and more because our equipment is much better now,” she says. “They’re not just Amazon.”
When Dada and colleagues began their new study, they aimed to test the cloud-forming ability of sesquiterpenes by mimicking forest air unpolluted by anthropogenic emissions. They started with a baseline measuring what happens after ionizing an atmospheric mixture of the most common “biological” volatiles, isoprene and alpha-pinene, a type of monoterpene. This combination produced clouds, as expected. Next, the team did the same thing and mixed in a sesquiterpene called β-caryophyllene. It is collected from pine and citrus trees and has a cracked pepper-like aroma.
Dada hypothesized that β-caryophyllene should chemically react to form an aerosol and eventually a cloud. She and her team stood in a control room and monitored 15 screens displaying real-time readouts of data such as aerosol size and concentration. You’ll know she was right when the particle size graph on one of her screens changes color. As the cloud seeds more, it grows and turns from blue to banana-yellow.
On the first run, the graph turned yellow. Dada was right. (“We were all screaming, ‘Banana! Banana! Banana!'” she recalls.) Adding just 2 percent by volume of beta-caryophyllene to the mixture stopped cloud formation. She doubled in size and the particles grew. Faster. This was the first experiment to demonstrate how sesquiterpenes produce clouds. Dada said that while these represent only a small portion of the compounds emitted by trees, the results showed that “their contribution is very large.”
“Adding small amounts of sesquiterpenes has a very large effect,” says Jiwen Huang, an atmospheric scientist at Argonne National Laboratory who was not involved in the study. Even if sesquiterpenes produce “ultrafine” aerosols that are not large enough to seed clouds, they can still affect the weather. In 2018, fans discovered that when giant rain clouds “capture” ultra-fine aerosols, they form new droplets, cheer up the thunderstorm.
For Huang, the new data suggests that sesquiterpenes could help better explain global flows of aerosols. Through aerosols, clouds move more heat away from Earth. This is an effect known as “radiative forcing.” (That’s the idea behind plot To geoengineers Aerosol Atmosphere: Artificial cloud seeding that can cool the ground. ) More aerosols mean clouds reflect more, appear whiter, last longer, and produce less rain.
But scientists have struggled to simulate how much aerosol to account for in their models. “It’s been a long-standing problem,” Huang said. “Many climate models overestimate anthropogenic aerosol forcing.” Perhaps that’s because they underestimate the prevalence of natural aerosols from microorganisms, plants, and trees before the industrial revolution. “Maybe what we’re using as a reference point is actually not as low aerosol as we thought,” Zuidema agrees.
By quantifying how trees create clouds, scientists can better predict the future and past of our climate. Industrial emissions reduce warming to some extent through radiative forcing, as sulfur aerosols can generate reflective clouds.However, if biological aerosols were more abundant than expected. in front As industrialization increases, the contribution from industry becomes less important.
There are so many moving parts to a dynamic climate that it is difficult to predict what this recalculation will tell us about global warming. For example, heat stress, extreme weather, and drought can affect plants by: Release more biogenic volatiles— creates more clouds. Deforestation and heat stress Promote tree line transition To higher altitudes and latitudes.it affects where Clouds form.
“It’s a feedback loop,” Dada says. “Climate influences the formation of clouds, and clouds influence climate.”
Better climate models can help scientists predict the best mitigation measures. “When you want more clouds, when you want less clouds,” Dada says. The problem, however, is that climate models are incredibly computationally demanding. Incorporating the physics of something as small as these tree aerosols may not be easy.
Dada returned to CERN this fall for further testing. Her team now wants to examine how anthropogenic emissions such as sulfur dioxide affect plants’ ability to form clouds. They may slow each other down or speed them up. Their goal is to extend their conclusions to areas that are less pristine than forests, where different types of emissions are mixed. “We’re adding in the human factor to get a more realistic view of almost any place in the world,” she says.
This story was originally wired.com.