The sky is not an ethereal, sterile realm. It’s teeming with bacteria, and scientists say that the microbes play a powerful role in producing rain and snow.While the idea that bacteria could prompt precipitation was previously known, a paper published this week in Science shows that they’re more important than anyone expected.
Researchers led by Louisiana State University microbiologist Brent Christner analyzed snow samples from around the world, categorizing the content of their “nucleators” — tiny particles that help water vapor coalesce and freeze.
All snow and most rain begins as ice. Though water is widely thought to have a freezing point of zero degrees Celsius, it’s not so simple in the clouds, where pristine vapors only bind to form ice crystals at exceedingly cold temperatures. Nucleators let crystallization happen in the less extreme conditions that prevail in much of Earth’s troposphere.
Christner found bacteria, technically known as “biological ice nucleators,” in an atmospheric context. High levels of bacteria were present in nearly every sample.
“Atmospheric scientists haven’t previously recognized that these particles are so widely distributed,” he said.
The findings raise the question of how climate change and human activities will affect bacterial balances in the sky. More immediately, they’re a starting point for research on bacterial contributions to cloud formation and precipitation.
In its latest report, the International Panel on Climate Change said that the impact of feedback loops involving clouds on global weather patterns are the “largest source of uncertainty” in current predictions of climate change.
Christner’s findings won’t overturn the IPCC’s fundamental conclusions — a high probability of dramatically rising global temperatures — but they should spur research that will help scientists predict the changes in greater detail, said Princeton University climate scientist Leo Donner, who was not involved in the study. …
The fact that bacteria could cause snow and rain was discovered almost by accident in the 1970s by study co-author David Sands, a Montana State University plant pathologist, during his research on Pseudomonas syringae, a microbe that causes ice to form on leaves.