03/03/2004
Helpful Shells
The beach on Marco Island is loaded with seashells of many shapes and sizes. This past month I’ve restrained myself and have picked up only a handful of shells and a couple of sand dollars. Until last week, I had not considered that the zillions of shells on and ground into this beach are representative of a significant contribution to combating global warming. This was brought to my attention when I saw a picture of seashells on nearby Sanibel Island in the February issue of National Geographic. Sanibel is well known for its shell-laden beaches.
The caption to the picture, part of an article by Tim Appenzeller titled “The Case of the Missing Carbon”, identifies the shells as a “lovely carbon reservoir”. The marine animals that build these shells and leave them behind when they die indeed perform a valuable service that helps to preserve our environment. A major culprit in global warming is the greenhouse gas carbon dioxide, CO2, which we humans generate in copious amounts through our various activities. The mollusks in the seas use CO2 dissolved in the water to manufacture the carbonate compounds that are major components of their shells. Long after the animals are gone the carbon still remains locked up in the shells.
The Geographic article does a fine job of illustrating the complex nature of global warming, especially when it comes to the generation and fate of the carbon dioxide attributable to human activities. As we charge into the 21st century, the concentration of carbon dioxide in the global atmosphere is on average about 370 parts per million. This doesn’t sound like much but it’s enough to affect the earth’s climate significantly. The atmospheric carbon dioxide level has been shown to have varied in cycles over hundreds of thousands of years. Generally, the more carbon dioxide the warmer the temperature.
With the advent of the industrial revolution, the carbon dioxide level rose to a bit higher values than the peak levels over the past 400,000 years. This might not be so worrisome except that today’s levels are about 30 percent higher than the industrial revolution levels, possibly even higher than at any time in the past 20 million years, according to the article! And, at the rate we’re going, the CO2 levels in the future will be much higher. Other greenhouse gases, such as the chlorofluorocarbons we’ve contributed to the atmosphere, don’t help the situation.
Unfortunately, global warming weaves a tangled web and some areas of our globe may benefit from the warmer weather and longer growing seasons. We’ve discussed the alternate possibility, that melting glaciers could shut down the global circulation patterns in our oceans, leading not to warming but to drastic cooling of certain areas in Europe, for example. This variation in the climatic effects of global warming can lull us into a sense of false security but eventually, if left unchecked, humanity as a whole will have to pay the piper and it may not be pretty.
If you follow even casually media reports on global warming, you know that one of the big problems is trying to figure out what happens to all that CO2 we spew into our atmosphere. The Geographic article states that we are responsible for adding some 8 billion metric tons of carbon dioxide each year. How do we accomplish this? We burn enough fossil fuels to account for 6.5 billion tons. These fossil fuels, notably oil and natural gas, have served to store huge amounts of carbon in the ground for millions of years and now it’s being released. The other 1.5 billion tons of carbon dioxide comes from burning forests to clear land, mostly in the poorer nations.
OK, we’ve dumped 8 billion tons into the air. But we’ve been lucky. Nearly 5 billion tons of it disappear, leaving only about 3.2 billion tons of extra carbon dioxide to warm us up. We’re getting off more lightly than we deserve but there’s a problem. We don’t know where all that carbon is going and, what’s worse, we don’t know if whatever is taking up so much carbon dioxide will keep it up. If it doesn’t, it’s going to be just too darn hot.
Where does the carbon dioxide go? Dickinson College, my undergraduate alma mater, is proud to have in its collection the burning glass of Joseph Priestley. Joe was an English minister who, back in 1774, used a burning glass to discover oxygen. But before he did this, he did some experiments that are key to our CO2 problem today. Priestly showed that a mouse in a sealed jar would die. We know that as the carbon dioxide it exhaled built up in the jar and the oxygen was exhausted the mouse suffocated. But then Priestley put a mint plant in the jar along with the mouse. This not only may have freshened its breath but the mint plant also allowed the mouse to survive. The plant took up the carbon dioxide exhaled by the mouse and used the carbon to grow itself. The oxygen in the CO2 was released, to be rebreathed by the mouse.
Although Priestly at that point didn’t know the identity of the gases involved, he had demonstrated the natural carbon cycle involving photosynthesis that is crucial to our existence. This same carbon cycle is responsible for one carbon sink, our expanding forests and grasslands that soak up CO2, turning it into wood and other plants. But, lest you think it’s obvious that the trees and plants serve as sinks for carbon, consider the fact that when leaves fall off the trees and when plants die, as they decompose CO2 is returned to the atmosphere. So, it isn’t necessarily true that a given swatch of forest will be a net sink for the carbon from CO2. It could even be a net source.
Surprisingly to me, the ravishing of our land by our forefathers here in the U.S. has apparently done us a favor. Today, in many cases, we are in the process of returning some of that land back to forests and grasslands. This new growth tends to lead to a favorable carbon balance. When a tree is growing, the wood that is formed uses up a good bit of carbon that stays relatively locked up as long as the tree keeps growing. When the leaves fall off and decay, they give off CO2 but there seems to be enough wood formed to make the forest a net sink for carbon. When the trees stop growing or growth slows down, as in a dry period, the balance becomes less certain and our sink can become a net source of carbon.
The oceans and our mollusks forming those shells are the other big sink for carbon. Carbon dioxide dissolves in water, making it more acidic. This carbonic acid is used, as noted above, to form the carbonates the mollusks incorporate in their shells. How long can this go on? The oceans have their own carbon cycles involving the plants and animals that live in them. All in all, it seems that the oceans take up about 2 billion tons of CO2 while the land plants take up a bit more. This leaves some of the missing CO2 unaccounted for. Obviously, accounting for anything on a global basis is a monumental task so it’s not surprising to me that there’s still some lack of balancing the books.
Remember old Joe Priestley? Another of his accomplishments was to develop a way of infusing carbon dioxide into water. In other words, for better or for worse, he invented carbonation and perhaps should be considered as the father of all sodas. We’ve all had the experience of opening a can or bottle of warm soda and having the stuff pour all over us. This illustrates that the solubility of CO2 in warm water is less than the solubility in cold water. As global warming occurs and the oceans warm up, the solubility of CO2 in the saltwater will also go down. I don’t imagine the oceans will start fizzing violently but the lesser amount of dissolved CO2 could become a problem. If the oceans dissolve less CO2, there will be less stuff from which our little mollusks can form their shells and less carbon will be stored in those shells.
If all this talk of global warming sounds like bad news, I’ve got some good news….. I just saved money by switching to GEICO! (Readers who don’t watch American TV will not recognize this as alluding to a TV commercial.) No, actually for me the good news is that I don’t have to give up golf. Last week I noted that, in an attempt to improve my golfing performance, I purchased a flea market 2-metal and 50 pre-owned golf balls. I’m happy to report that the technology of the 2-metal design indeed has allowed me to clear at least some of the water hazards. I only lost half the dozen or more balls that I lost in my previous round at the same course. Staying away from the water’s edge is also a good safety strategy here, what with the alligators prowling the waters.
Allen F. Bortrum
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