For the rain to fall, the water and clouds have to freeze. But pure water doesn’t always freeze at 32 degrees Fahrenheit. It can reach temperatures as low as negative 40 before freezing while clouds hover around five degrees. To crystallize, water molecules need something to hold on to enter bacteria. Some plant pathogens are coated with proteins that bind to water molecules. It helps water freeze at warmer temperatures. Sometimes these bacteria are swept up into the clouds by wind currents.
Some scientists believe they may have a saying when they come back down. By latching on to water molecules, bacteria can initiate ice formation in the clouds and trigger rain. This process is called bio precipitation. Researchers don’t completely understand the chemistry of what the ocean dispatches into the atmosphere, but they know there are many compelling reasons to study it.
How bacteria make rain?
Bacteria are everywhere, on every surface of everything, all the time. They can live in the air down here, but they’re tiny after all and thus can be easily picked up by the wind. Bacteria have been found almost 25 miles up and all over in the clouds! Scientists have found bacteria living above rainforests and deserts, mountains, seas, even inside hail and snow!
They help in cloud formation and can even live in lightning-prone storm clouds to encourage rain or hail. Researchers have found as many organisms in parts of the sky as in an average river. Clouds look pure and pretty, but they’re teeming with bacteria, algae, fungi, and other tiny plants and animals on the micro-level.
Microorganisms may see clouds as a giant transportation system, growing and multiplying so the colony can populate a new area, “piggybacking on the hydrological cycle,” said one scientist.
The composition of aerosol particles in the atmosphere and the relationship of that chemistry to weather are mysterious. When people think of aerosol particles in the sky, they usually think of soot, the small, carbon-rich chunks that come from burning fuels like wood and gasoline. The dark particles in the atmosphere can absorb radiation from the sun and warm up the planet. But there are also natural aerosols: dust from deserts, particles formed with the help of fragrant terpene compounds from forests. These natural particles can also contribute to global heating and cooling, and they play an important role in precipitation.
When it comes to sources of natural aerosols, it makes up more than 70% of the Earth, and so much of its chemistry is still a mystery. The ocean sprays salt into the sky! But most of what the sea sends up is an organic material, things like proteins, lipids, and even bacteria. There’s a really thin layer that coats the entire surface of the ocean. It’s less than a millimeter thick. There’s a lot of hydrophobic organic material. The ocean can easily kick this stuff out into the air through waves crashing and air bubbles bursting.
When it comes to bacteria, though, the ocean isn’t throwing things out willy nilly. The ocean appears to shoot certain bacteria out preferentially. That’s a compelling mystery and that certain bacteria, such as Pseudomonas syringae, can help make it rain. Scientists call them bioprecipitation. The ocean and other natural sources can launch bacteria high enough into the atmosphere to join other aerosol particles. It helps ice crystallize and form clouds which are rainmakers.
At the center of every cloud drop, at the center of every ice crystal, is a particle. Only one in a million particles in the atmosphere will form an ice crystal. And there’s something very magical about the chemistry of those particles that do. That’s the big question that chemists work hard to try and answer. The chemistry of natural aerosols could be particularly magical.
Atmospheric chemists joined forces with meteorologists and found that storm clouds grown naturally with bacteria. And desert dust appears to drop more precipitation than clouds seeded with other aerosols, such as those from pollution. Understanding the chemistry of natural aerosols could therefore help us learn to grow better rain clouds. It is something we’ve worked on since the 1940s.
Frequently asked questions
How do mushrooms make it rain?
In a single day, one mushroom can catapult millions of tiny spores into the air. And not only do these spores help seed baby fungi, but they also help seed clouds. That’s because, to form clouds, moisture in the air needs microscopic particles to glom onto, like airborne dust, sea salt, or pollution. But in places with lots of life, rain-making particles are often biological in origin, like bacteria, pollen, plant fragments, and spores from mushrooms.
Earth has so many mushrooms intent on reproducing that there are a billion spores above every square meter of its surface. Many of these spores drift high up into the atmosphere. They provide scaffolding for water to condense onto seeding rain droplets and ice crystals. It forms in literal mushroom clouds.
How much bacteria is in drinking water?
According to their paper in Applied Microbiology and Water Resources, our drinking water has eighty thousand bacteria per milliliter and a couple thousand more bacteria species in the pipes themselves!
Using flow cytometry, a laser-based system, scientists counted what was previously uncountable: every tiny particle flowing through our water pipes. Then using DNA sequencing, they uncovered a vast diversity of bacteria lurking behind our faucets.
Which bacteria lives in water?
Researchers isolated four microorganisms commonly found in drinking water: Sphingobium, Xenophilus, Methylobacterium, and Rhodococcus. These are primarily harmless genera of bacteria found in soil, on leaves, and in lakes. Drinking water is fed by snow and rain, which streams down mountainsides to rivers pumped, diverted, or dammed to supply drinking water.
Brent Christner, “LSU scientist finds evidence of ‘rain-making’ bacteria”. American Association for the Advancement of Science.
Christine Dell’Amore, “Rainmaking Bacteria Ride Clouds to “Colonize” Earth?”. National Geographic.
Halsall, Mark, “Snomax: Need more snow?”. Snow Grooming Magazine.