How climate change is altering petrichor, the glorious smell after it rains
Scientific American · LC · trust 58/100
How climate change is altering petrichor, the glorious smell after it rains
As the planet changes, so will this nostalgia-triggering scent
The distinct, earthy smell that fills the air after rain following a long dry spell can trigger some serious nostalgia. This scent, petrichor , goes right to our brain’s memory and emotional centers for reasons that may be to do with our very evolution. But as climate change alters Earth’s weather and environment, petrichor is going to transform, too.
First, it helps to know why petrichor even happens. During dry periods, soil-dwelling bacteria produce a compound called geosmin that deters insects such as fruit flies. The chemical signals to the flies that the plant material the bacteria grow on isn’t appetizing and that it might be toxic. Geosmin also attracts spore-spreading animals, such as springtails, which help disperse the compound even more widely.
“Humans are extremely sensitive to geosmin,” says Johan Lundström, a psychologist specializing in olfactory perception at the Karolinska Institute in Sweden. “If there was one drop of geosmin stirred up into an Olympic-sized swimming pool, we’d still smell it.”
If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
While bacteria in soil produce geosmin, plants discharge aromatic oils during a drought to create a shield to protect against harsh heat and minimize water loss. When raindrops hit dry ground and plants, the impact creates microscopic bubbles filled with geosmin and oils that rise into the air, pop and scatter into tiny particles that can then fill human nostrils.
Exactly how petrichor changes will depend on where you are as the effects of rising global temperatures on weather and climate patterns will vary from place to place and year to year. Overall, parts of the world that get more rainfall will experience less petrichor, whereas areas that have droughts will experience more, says Jeppe Lund Nielsen, a professor of microbial physiology at Aalborg University in Denmark.
Droughts cause geosmin to build up, and when they occur with hotter temperatures, bacteria produce even more geosmin as heat speeds up chemical reactions inside the microbes. “If you get a higher temperature, you also get a higher production of the compounds,” Nielsen says. So when it finally does rain, more geosmin is released. But if soils get too dry, “the geosmin will dry up and not be released,” Lundström says.
Where rain falls more frequently, there will be less petrichor because the aromatic compounds won’t have enough time to accumulate. And heavy downpours—which are increasing as the planet warms—are too forceful to trap the tiny air bubbles required to launch the scent into the air. Instead the compounds are diluted, pushed underground or mixed in surface floodwaters.
Soil degradation—which has also increased as a result of higher temperatures and heavier downpours—plays a role, too, because it means fewer geosmin-producing bacteria can grow.
Any changes to geosmin won’t stop at what humans smell. Insects that react to petrichor will also have to adjust their behavior, Nielsen says. For example, areas with large amounts of petrichor will likely see an increase in mosquitoes, because the smell indicates to these insects that the dry ground is now a moist fertile environment in which to lay their eggs.
Gregory Wakeman is a writer from northern England, now based in Washington, D.C. He has written for the BBC, the New York Times, the Guardian, National Geographic and Smithsonian, to name but a few, all while defiantly keeping his accent.
Great science journalism requires human expertise, time, effort and creativity. And it costs money. That’s why I and the journalists here at Scientific American hope you’ll join our community.
When you subscribe, you are supporting staff and freelance journalists who are passionate about telling science stories that are true, important and compelling. Our editors and reporters are often experts in their fields, which means they understand the nuances of big discoveries and can untangle the breakthroughs from the hype. With a subscription, you are also supporting rigorous fact-checking to ensure the words we publish are precise and accurate. And you’re supporting original illustrations, graphics and photos that bring you closer to an advanced laboratory, an ice sheet in Antarctica or a space mission in orbit. You’re helping us craft other types of high-quality journalism as well: Our newsletters are carefully written, edited and curated by staffers you have or will come to know and love. Our Science Quickly podcast is based on original reporting, collaboration with editors and scientists and exacting production.
Subscriptions keep this engine running so we can continue to deliver thoughtful, rigorous and independent science journalism to you. In an era of viral misinformation, this work is crucial. If you value what we do, I hope you’ll consider joining us as a subscriber
Jeanna Bryner, Editor in Chief, Scientific American
Read the original at Scientific American →
Open in TruthVane →