I've often wondered what happened to the carbon dioxide emitted from various natural sources, including volcanoes which can spew out in few days what it takes a coal-energy plant an entire year to emit. Don't these natural 'emissions' themselves contribute to global warming? Was there such a thing as stability of carbon dioxide in the atmosphere before humans came along?
There are some answers to these questions in a new study reported in Nature Geoscience this week. It is to do with minerals and molluscs. Scientists have found that when CO2 levels in the air rise, silicate minerals found in soil begin to break down faster, and this releases calcium ions. The calcium ions then dissolve in water and get washed to the oceans by rain and rivers, where the molluscs await.
To make their oh-so-pretty shells of calcium carbonate, these little creatures use both the calcium and the carbon dioxide dissolved in the water, thus taking them out of the system.
The study used air bubbles trapped in Antarctic ice as far back as 610,000 years ago, and found that for all this while the balance of CO2 in the atmosphere was never off by more than one or two percent. Until, of course, we clever beings came along. The researchers say this delicate system "probably helped to prevent runaway greenhouse and icehouse conditions over time scales of millions to billions of years — a prerequisite for sustaining liquid water on Earth's surface."
“The system is finely in tune,” says Ken Caldeira (one of the two authors of the study). “That one or two percent imbalance works out to an average imbalance in natural carbon dioxide emissions that is thousands of times smaller than our current emissions from industry and the destruction of forests.” (Carnegie Institution for Science)
Volcanoes and hydrothermal vents add about 0.1 billion tons of carbon annually to the atmosphere and oceans. A quantity that other natural systems are able to harness and balance. But human activity pumps out a staggering 10 billion tons of carbon each year. Clearly, we need to clam, er clean, up our act.