In hopes of slowing down the progression of global warming, some scientists have suggested that the carbon dioxide (CO2) pollution expelled by powerplants could be captured and stored before it enters the atmosphere; at which point it could be liquefied, and pumped deep in the ocean. There, they hope that the extreme pressure will prevent the CO2 from rising back to the surface, because such an event would not only defeat the purpose, but it could also be catastrophic.

There is an event called a “limnic eruption” which can occur when water becomes oversaturated with carbon dioxide. Some paleontologists have suggested that such an eruption may have been responsible for the greatest mass extinction in Earth’s history, which occurred about 252 million years ago. In recent history, hundreds of people have died from limnic eruptions in small lakes, most of them from two events in the mid-1980s in lakes Nyos and Monoun near Cameroon, in western Africa.

In each case, volcanic vents on the lake bottoms slowly allowed carbon dioxide to seep into the water, which absorbed the gas over a period of years. When the water became oversaturated, the lakes released the gas in a chain-reaction eruption, and created a dense, invisible cloud tens of meters in height. The huge blanket of CO2, which is heavier than oxygen, flowed down into low-lying valleys and asphyxiated all who dwelled there. The 1984 event took 37 lives, and the 1986 event killed almost 1800 people. The normally clear lakes turned rust-colored, and the vegetation on the lake shores was severely disturbed by the waves and strong winds of the eruptions.

Once the cause of the eruptions was discovered, efforts got underway to prevent future catastrophes there. Lakes in the region now have fountains in place which expel the carbon dioxide into the atmosphere are a more regular rate, preventing the buildup of CO2 in the lake water.

Now, with some scientists suggesting the oceans as a possible long-term dumping ground for excess CO2, researchers are testing the viability of the approach. A researcher at the University of Michigan named Youxue Zhang has performed experiments that indicate that the minimum safe depth to prevent CO2 from rising to the surface would be about 800 meters down– about half a mile– but possibly as much as 3,000 meters, which is just short of two miles.

From the University of Michigan News Service article:

“Droplets injected to a depth of 800 meters will rise, but if they are small enough they should dissolve completely before reaching the liquid-gas transition depth—assuming everything works perfectly,” said Zhang, a professor of geological sciences. However, at a high injection rate, seawater full of CO2 droplets would have an average density smaller than that of surrounding seawater, creating conditions that could lead to a rapidly-rising plume. Problems also could occur if the injection device malfunctioned, producing larger droplets.

Of course all of these data are based on computer models, and cannot possibly account for every possible variable, so one cannot have complete confidence in the results. But perhaps this does afford a way to dispose of some excess CO2 and slow down the progression of global warming, at least in the short-term.

Trying to bury away our troubles in the oceans is certainly a problematic and irresponsible approach, but it may serve as a stop-gap while measures are taken to reduce overall carbon dioxide pollution. But considering the deadly examples of lakes Nyos and Monoun, one hopes that humankind will not be foolish enough to adopt this solution in the long term.

Links:

University of Michigan News Service article Background on the limnic eruptions near Camaroon in '84 and '86

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Written by Alan Bellows, posted on 11 November 2005. Alan is the founder, developer, designer, and managing editor of Damn Interesting, and he likes the Oxford comma.