The Carbon Cycle and the Global Climate System
Sep 8, 2005
Popular Products in Sport and OutdoorThe Bottom Line A vast problem that will not be solved by half-vast ideas!
Carbon is life and life is carbon, at least as it exists on this planet. The composition of the Earth, in total, is 0.19% carbon---but living things, plants and animals, average 18% carbon. Carbon is the principle building block for living molecules, both plant and animal. So where does carbon come from?
Carbon exists in a cycle, but for the sake of discussion I'll say that carbon comes from carbon dioxide in the atmosphere. Plants absorb carbon dioxide and use sunlight in the process called photosynthesis to convert carbon dioxide into complex plant matter, and produces free oxygen in the process. So vegetation of all kinds removes carbon dioxide from the atmosphere and releases oxygen.
Plants die and decay, and the carbon again combines with oxygen to form CO2 once again. Some plants are consumed by animals, many of which remove oxygen from the air and release CO2 in the respiration process. The carbon from the plants and from other animals up the food chain is converted to complex animal matter. When animals die their bodies decay and the carbon is again converted to carbon dioxide.
But some of the animal and plant matter is processed over millions of years in a geologic process to form coal and oil, held in the Earth's crust and taking carbon "out of circulation" for eons. So there are actually two carbon cycles that overlap: a biological cycle and a geological cycle. And the two have interacted for millennia to maintain a robust balance between carbon, oxygen and other elements in a way that perfectly supports life.
Then along has come an animal species that is disturbing the carbon cycle by extracting coal and oil from the Earth's crust in huge volumes, combining it with oxygen to produce energy, and releasing an "unnatural" amount of CO2 into the atmosphere. Scientists have devised ingenious methods to track the concentration of CO2 in the atmosphere for the past 160,000 years. On that time scale, the data show that the level has cycled between 200 and 300 parts per million (ppm) two or three times. The low points roughly correspond to the ice ages.
Since 1700 the concentration of CO2 in the atmosphere has increased dramatically from about 300 ppm to 400 ppm, the effect of human activity, primarily burning of fossil fuels, and clearing of forests for agriculture. Generally accepted figures are that burning of fossil fuels has increased the release of CO2 by over 5 billion tons per year over the "natural" level. Deforestation is thought to have decreased CO2 uptake by another 3 billion tons per year. The increase in atmospheric CO2 is only about half of what would be expected by these human activities. The difference is evidently not well understood and there are competing theories to explain why the CO2 increase is only half of what would be expected from measurements of man-made CO2 being released into the atmosphere. Of course the cycle is extremely complex and quantitative measurements are subject to very large errors. The general explanation is that some CO2 is being absorbed by an increased amount of vegetation and ocean plankton---somewhere.
Scientists extrapolate the present rate of increase in atmospheric CO2 to lead to a level of 600 ppm, double the "natural" level by the year 2100. The addition of that much CO2 to the atmosphere is projected by scientists to have many effects, some positive, some negative, and some disastrous. The effect that gets by far the most attention is the projected effect on the global climate system.
The global climate system is extraordinarily complex, and strongly influenced by thousands of variables. The global climate has it's own cycle with "natural" causes like the circulation of warm ocean waters, leading to concepts like "el nino," that are very subtle but can have a major effect on worldwide climate, in ways that scientists are only beginning to understand.
Climate scientists have put together huge global climate models that can be simulated on large-scale computers. These models have been refined over recent decades to the point that variations predicted by the models can be at least partially confirmed by observation and measurement. This, of course, is a necessary part of establishing the validity of these highly sophisticated simulation models. The global climate they are trying to simulate is orders of magnitude more complex than the model. Since we are trying to predict and measure the effects of relatively small changes in only a few of thousands of variables the problem is mind-numbingly difficult.
Notwithstanding the difficulties, a consensus has developed that the models are making a valid prediction of the effects of CO2 concentration on climate, and that these predictions are being confirmed by observation and measurement.
The effect of CO2 in the atmosphere is to change the way the sun's energy is absorbed by Earth and reflected back into space. Increased CO2 inhibits the radiation of heat energy, reflecting it back to Earth and creating a "greenhouse" effect. With all the temperature variations around the Earth, the variations from night to day, and from season to season, it is easy to grasp how difficult it is to measure any actual change in the average temperature of the Earth. But there is scientific concurrence that since 1900 we can measure that the Earth has warmed by about one degree Fahrenheit! Furthermore, that small amount of change is consistent with the change predicted by the simulation models, holding everything constant and increasing the CO2 content of the atmosphere by an amount equivalent to the measured increase.
Those results give scientists confidence in their prediction that when CO2 concentrations reach 600 ppm in 2100, it will cause a warming of the Earth of 4 to 5 degrees Fahrenheit. Doesn't sound like much? Well, scientists have also put together scenarios to predict how the world will change with that amount of warming. Melting of the polar ice caps will increase the sea level by several feet, changing every coastline in the world, and completely inundating the state of Florida, for example. Warming of the oceans will change ocean currents and stimulate much more frequent and more severe hurricanes. Rainfall worldwide will be drastically changed, some areas getting more and others less.
Some may benefit from those changes, and others will be drastically impacted, or even wiped out. But there's no doubt that warming of only a few degrees would change the world very dramatically!
The issue with regard to global warming is whether the observed warming to date has actually been caused by CO2 and other man-made greenhouse gases like methane and chlorofluorocarbons---or whether the increase is part of a "natural" global climate cycle caused by "natural" causes like sun spot activity, for one example. Detecting a man-made (or anthropomorphic) component of observed warming is like trying to detect a very small signal buried in a lot of random noise, and a lot of other signals. Not too unlike trying to seperate fly droppings from pepper, as the old analogy goes.
There are many legitimate pros and cons that warrant discussion of the whole subject of global climate change and what, if anything, could be done about it. There is little disagreement that it would be desirable and prudent to replace fossil fuels with a different form of energy production; but the problem is that the production of energy from fossil fuels is far, far less expensive than any other available technology, and the demand for energy is increasing at a rapid rate worldwide.
Using less energy through conservation and better efficiency will help, but will be overwhelmed by increasing energy use in developing countries like China. Some advocate a drastic change of culture and the modern way of living, but that's not going to be widely adopted anytime soon.
My confidence is in technology. As fossil fuels become more expensive other solutions become more feasible. As global warming caused by CO2 is proven, means of removing, or sequestering, CO2 are being developed. As one example, I recently saw a brief article of a device described as a "synthetic tree," capable of removing 1000 times as much CO2 as a living tree, an amount that would eliminate the CO2 emissions of 15,000 vehicles.
Geneticists have spoken of adapting algae to use photosynthesis to produce hydrogen directly, leading to enough fuel for 200 million vehicles from an area of pond scum 100 miles on a side. Wow!
But for now we're stuck with fossil fuels and continued worry about global warming. The Kyoto Accord is a non-answer, and will never be accepted, in my opinion. Let's get over politicizing the subject, and be serious about balancing conservation, production, research and development for now!