Cloud seeding, the science of stray particles forming rain, may have an unlikely foe in its territory – marine pollution.
The research says that marine pollution reduces the ability of aerosols to seed clouds by about a third, indicating that ocean biology will be key in finding answers to the growing threat of climate change.
Aerosols, science says, are tiny atmospheric particles that influence the likelihood of rain formation by absorbing or reflecting sunlight, a chemical process that is referred to as cloud seeding.
Marine aerosols occur when ocean waves break, forming tiny air bubbles which rise to the surface and burst, releasing gases and the particles into the atmosphere, science says.
Meteorologists define cloud seeding as a technique that enhances rainfall by introducing particles, often dry ice or silver iodide crystals, into cloud systems to influence water vapor condensation into raindrops.
Silver iodide lowers the temperature in the cloud and provides more ice crystal seeds, but doesn’t freeze all of the liquid water, either.
At the same time, ice crystals grow from the liquid freezing onto them and then the ice lumps together, then fall and create snow where they can produce rain if they melt before reaching the ground, officials say.
“The chemical substances are dispersed into the air by aircraft, ground generators or rockets,” explains the climatologist Peter Ambenje. “The process can also be used to dissipate fog and weaken storms.”
Using this background, scientists engineered the breaking waves of natural ocean water under purified air in the laboratory, according to a study published in the online edition of the Proceedings of the National Academy of Sciences on April 22, 2013.
They were able to isolate and analyze aerosols from the spray and determine how life within the water altered the chemistry of the particles, the study says.
Quoted in the Science Daily, 2013 April edition, Kimberly Prather, the research team leader said their investigations were able to establish that ‘as the seawater changed and bacteria levels increased the composition of the aerosols changed in ways that reduced their ability to form clouds’.
“This would indeed suggest that if pollution caused significant increases in bacteria levels, it could affect cloud seeding, and by extension the frequency and intensity of rainfall,” observes Vincent Sweeney of United Nations Environment Programme (UNEP).
However, as the Coordinator, Global Programme of Action for the Protection of the Marine Environment from Land Based Activities (GPA) Division of Environmental Policy Implementation (DEPI), Sweeney adds that: “To what extent it will affect rainfall is the big question.”
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For instance, he says, there are still many unanswered questions such as: Would it be localized or more regionally or globally? What is considered a ‘significant’ increase, or what concentration would need to be present in order to affect the composition of aerosols?
“It is important to remember that bacteria concentrations would be highest near to the pollution sources, that is, nearer to the shore,” argues Sweeney. “The weather patterns are more affected by open ocean issues and therefore pollution from land based sources may have little effect on bacteria concentration in the open ocean.”
But Prather and his team of more than 30 scientists are more hopeful than doubtful.
Findings of the April report explain that the laboratory tests were able to first eliminate other sources of contamination from the ocean sample, a technique that allowed them to probe sea spray aerosol directly for the first time right after it was produced by breaking waves.
According to the report, it took another five days to alter biological communities within the flume by adding various combinations of cultures of marine bacteria and microscopic marine algae, or phytoplankton.
Then, it says, as a hydraulic paddle sent waves breaking over an artificial shoal, instruments positioned along the 33-meter long flume analyzed the chemistry of the seawater, air, and aerosols.
“This is an important finding because current estimates of biological activity in surface waters of the ocean rely on instruments aboard satellites that measure the color of the sea surface, which changes along with levels of chlorophyll, an assessment that will miss blooms of other organisms, such as bacteria,” they conclude.
However, some scientists are not convinced. Dishon Murage, a marine scientist, argues that rain formation from ocean activity still owes its life to recirculation, air pressure and surface temperature.
According to him, these are some of the activities that have for long been used to generate accurate data and map the patterns of the el Nino and la Nina phenomena.
While el Nino refers to a condition where there is possibility of the region experiencing heavy and prolonged rains, la Nina refers to a dry time stretch which is likely to result into drought, he says.
“I am doubtful about marine pollution affecting rain seeding because no such kind of study has been conducted in the regions I know,” argues Murage.
When did it Start?
|Cloud seeding can be done by ground generators, aeroplanes, or rockets.
Cloud seeding first began in the mid 1940s when Vincent Joseph Schaefer was studying cloud formation for General Electric and its ability to enhance precipitation, dissipate fog, modify hurricanes, and decrease lightning and hail in thunderstorms.
His studies formed the foundation for present day science where cloud seeding has been used to evaporate fog at airports by adding large quantities of dry ice which causes the fog to dissipate and clear the air.
Russian scientists say they have successfully used the technique to suppress hurricanes, although US scientists dispute the claims arguing they are inconclusive from experiments conducted in the early to mid 1900s.
At the 2008 Summer Olympic Games, Beijing used cloud seeding to clear pollutants from the air and keep it from raining over the Bird’s Nest Stadium while the games were going on.
It can also occur naturally when fall streaks composed of ice crystals from Cirrus clouds fall into Cumulus or Stratus clouds lower in the atmosphere. The ice crystals act like seeds to start the formation of larger crystals which lead to raindrop formation, science says.
However, the use of cloud seeding is controversial. A section of the scientific community say it isn’t worth the resources, because even the most dramatic rainfall increases only amount to five to 20 per cent.
Others say it could reduce the amount of rain that might have fallen through dissipating clouds, hence, reduction of rainfall downwind and negatively impacting on the natural ecosystem.
For now, both scientific fronts appear to have a fair grasp of their arguments, but it will be further research that will culminate to answering the lingering questions about climate change and artificial rain making, concludes Sweeney.
This article was first published in 2014 and is currently republished for its importance.