Microscopic bacterial particles couched in clouds have been found to catalyze rainfall. To make it rain, clouds ordinarily have to first form ice crystals, however pure water droplets stubbornly remain liquid in temperatures as low as -40°C in the atmosphere.
"It has long been a paradox that lots of ice-containing clouds form at temperatures warmer than –15 °C,” says Brent Christner, a researcher at the University of Florida in Gainesville. “We now think that bacteria may be at least part of the explanation.”
In the 1970s pseudomonas syringae was discovered, otherwise known as an “ice nucleator”, which employs membrane ice-nucleation proteins (INPs) to form ice crystals at relatively high temperatures. Whilst investigating a persistent wheat blight in Montanta in 1978, scientist David Sands captured these ice nucleators in a petri dish midflight, leading him to develop a theory that rainfall may be born from bacteria - naming the process bioprecipitation. However atmospheric scientists at the time did not give the notion much credence, preferring to focus instead on the role of minerals in dust.
Bioprecipitation remained a fringe theory until recent research awoke interest in the atmospheric microbiome. These are the bacteria and fungi carried into the sky by clinging to soil and dust particles, as well as microscopic phytoplankton launched into the atmosphere by breaking sea waves. The atmospheric microbiome’s role in regulating rain and snowfall is now being unravelled; raising hopes that clouds might be persuaded to precipitate at our convenience.
How might human practice wage alterations in the weather? Research suggests that intensive industrial agriculture and factory farming which employs glyphosate and glufosine may play previously unsuspected role in triggering drought and severe weather patterns. Sands believes that concentrating crop cultivation on one or two variants rich in ice-nucleating bacteria can actually constipate the clouds - if too many ice nuclei are formed, they never grow large enough to rain. This may have happened during the 1930s dustbowl in the US, when epidemics of wheat rust plagued the prairies and millions of ice-nucleating spores were released by ploughing into the atmosphere.
Sands' ambition, with research partner Cindy Morris, is to find the ideal balance of ice-nucleating bacteria to regulate rainfall. Bioprecipitation looks more promising than the standard cloud seeding technique that uses silver iodide and has little evidence to show that it actually increases rainfall. However the possibilities of bioprecipitation are certainly not limitless and will not dissolve our droughts. One can’t draw showers without water vapor, meaning in severely water scarce regions this technology may not be of great use. On the other hand could damaging deluges be avoided?
In the era of anthropogenic climate change, reliable rainfall is more or less recent history. Man is turning to new strategies to manage water resources, tactics include adjusting our lifestyles, making production practices more water efficient, as well as more extreme approaches like building mountains. What is clear is that we are in increasingly short supply of that which is indispensable to our survival, meaning desperate decisions lie on the horizon. Two thirds of the global population, 4 billion people, already experience severe water scarcity at least one month of the year. Research suggests geoengineering methods are likely to take a toll on global rainfall patterns, triggering extreme precipitation events. Assuming we can tweak a dial on rainfall, a familiar water woe question surfaces: how do we ensure that one community’s gain is not another’s loss?
Image credit: Bryce Bradford
New Scientist “Rain makers: How high-flying bacteria could control the clouds” (April, 2016)
Signs of the Times “Atmospheric dysbiosis: Is the loss of rainmaking bacteria causing the drought in the Western US?” (July, 2015)
GeoSpace “Study: Most rain comes from ice clouds” (July, 2015)