Rain

[awakening2lite]

Airborne Bacteria Make It Rain, Researchers Find

By Brandon Keim 02.29.08 | 4:45 PM

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The green dots indicate Pseudomonas syringae bacteria suspended in ice. Like other so-called biological ice nucleators, P. syringae gives water vapor a place to meet, join and form ice crystals that later fall to Earth.
Brent Christner/Louisiana State University




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.

Donner agreed that climate scientists had not appreciated the ubiquity of precipitation-causing bacteria in the atmosphere.

"One of the real uncertainties in the climate system is how cloud particles are nucleated," he said. "Climate models need information on nucleators. This is especially relevant for understanding how clouds change as atmospheric composition changes."

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.

Unable to discover the source of repeatedly infected fields, Sands exasperatedly took to the skies. He did the scientific equivalent of dragging a cup through the clouds -- and lo and behold, there was P. syringae.

P. syringae is not the only biological ice nucleator, but it is the most common, and all varieties share a protein structure that provides a scaffold for free-floating water molecules. Once bound to the bacteria and to each other, the water vapors are able to freeze, and eventually fall back to Earth.

In a pure state, water vapors freeze at temperatures below -35 degrees Celsius. Nucleators allow this to happen in warmer conditions, and Christner's study found that bacteria are the most common warm-temperature nucleators of all.

Researchers never realized bacteria could be so widespread in the clouds, said Christner, because the technologies used to measure fine dust -- traditionally seen as the most important nucleator -- ignore microbe-sized particles.

"It's not that these atmospheric scientists are idiots -- they're not," he said. "But biological nucleators were not previously recognized as being that abundant or important. They're going to have to revise that."


http://www.wired.com/science/planetearth/news/2008/02/bacteria_clouds

[awakening2lite]

Plankton Cool Off With Own Clouds

Amit Asaravala 07.16.04 | 2:00

Phytoplankton may be small, but that doesn't mean they can't do big things -- like change the weather to suit their needs.

A recent study funded by NASA's Earth Science Department shows that the tiny sea plants release high quantities of cloud-forming compounds on days when the sun's harmful ultraviolet rays are especially strong. The compounds evaporate into the air through a series of chemical processes that result in especially reflective clouds. This, in turn, blocks the radiation from bothering the phytoplankton.

The findings not only confirm earlier theories that plankton are linked to the creation of clouds above the ocean but could also lead to a better understanding of how living things affect the Earth's climate.

"The take-home message is that all the processes that are going on in the ocean and the climate are very tightly connected," said David Siegel, co-author of the study and director of the Institute for Computational Earth System Science in Santa Barbara, California. "This is really the impetus for other researchers to look into the whole cycle of how biology and climate interact."

Siegel and Woods Hole Oceanographic Institution researcher Dierdre Toole announced the results of their study in the May issue of the Geophysical Research Letters, a scientific journal.

The two researchers performed the study on measurements taken off the coast of Bermuda. There, they found that the ocean levels of a compound called dimethylsulfoniopropionate, or DMSP, were directly related to the level of ultraviolet radiation reaching the phytoplankton that live near the ocean's surface.

DMSP is an important link in the plankton-to-cloud cycle because, as it leaves the phytoplankton cells and enters into the water, bacteria break it down into a chemical called dimethylsulfide, or DMS. Evaporated water, in turn, carries the DMS into the air where the chemical reacts with oxygen to form various sulfur compounds. These compounds collect as dust particles that promote water condensation, which, finally, leads to cloud formation.

The entire process takes place very rapidly, ensuring that the plankton aren't under the sun's rays too long. In their study, Siegel and Toole found that the upper layer of DMS in the atmosphere could be replaced in just a few days.

That the process happens at all may be a sign that the Earth is better prepared to handle climate forces like the depletion of the ozone layer, which also blocks ultraviolet light, than previously thought. However, Siegel believes it's too early to make such assessments because it's unclear just how widespread the phenomenon is. It's also unclear just how much ultraviolet light and other forces the system can tolerate.

The researchers now plan to create computer models that explore how the presence and absence of phytoplankton might change the climate. They also hope to add to their study by using information from NASA's Sea-viewing Wide Field-of-view Sensor mission, which collects data on shifts in visible light reaching the ocean's surface.

It's possible that the extended work will show that phytoplankton do affect climate on a global scale, said Siegel.

If that's the case, it's also possible that scientists who like to talk about the "butterfly effect" -- the theory that the flapping of a butterfly's wings in one part of the world could eventually lead to violent weather patterns in another -- may soon find that it's more hip to talk about the "phytoplankton effect."

http://www.wired.com/science/discoveries/news/2004/07/64239