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Earth Sense: Long-term effect of CO2 levels unknown
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In the debate about rising atmospheric CO2 levels, it’s rarely mentioned that there’s a host of unknown factors. That’s not a reason to lay back and continue business as usual. 

But atmospheric carbon dioxide doesn’t get there and simply stay there. It’s part of a much bigger picture: the global carbon cycle. The oceans have a lot of it dissolved in the water, just like the carbonation in an unopened bottle of soda pop. If you open the bottle and set it in the sun, the drink will lose its fizz over time.

The CO2 goes from the dissolved state (carbonic acid) into a gas, which lets it escape into the atmosphere. In this manner, warming of the world’s oceans could further increase CO2 levels.

But the unknown factor is plant life. There’s no good way to predict what ocean- and land-based plants will do when there’s more carbon dioxide available, which they love. Plants use CO2 as a nutrient for cell growth. In that way, a carbon-rich atmosphere could actually be beneficial by encouraging forest growth.

Another unknown factor is soil CO2. The layer of topsoil above the bedrock has its own atmosphere, contained in its many pore spaces. The roots of trees and other plants enrich it with carbon dioxide. What the effect of rising concentrations in the free atmosphere would be is unknown.

In the Lafayette area of northern Georgia, the bedrock is limestone. I’ve measured soil CO2 levels as high as 2 percent, which is quite normal. Increased activity by the trees could raise it higher. But that wouldn’t result in climate change.

The soil CO2 forms carbonic acid (like filling that soda bottle with fresh soda). This acid migrates downward and dissolves some of the limestone. This makes what’s known as “hard water,” rich in calcium, carrying the lime away.

Eventually, it drops out of solution again and forms new rock. That can happen in a cave, where you see stalactites and stalagmites as a result. Some calcium is carried all the way to the ocean, where it builds new ocean floor.

Simply speaking, in a very slow process, atmospheric CO2 is in part converted into bedrock and, at some point, mountains when that rock rises from the sea. Lookout Mountain came into existence that way. But what effect the increasing world CO2 levels will have on this carbon cycle is still unknown.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays.

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