One of the most popular environmental problems is the global warming caused by the greenhouse effect, though most of the people are not sure what bad effect it will have on us.
1. What is the global warming?
The greenhouse effect is a natural process by which some of the radiant heat from the Sun is captured in the lower atmosphere of the Earth, thus maintaining the temperature of the Earth’s surface. As an actual greenhouse does not capture heat inside, this metaphor is not appropriate, but we must use this generally established term.
The most influential greenhouse gas is not carbon dioxide, which absorbs only a part of infrared spectrum, but water vapor, which absorbs most of infrared spectrum. We can attribute 67% of the greenhouse effect to water vapor. Next to carbon dioxide, methane, which is generated from decomposing organic matter without oxygen, is the third most important cause of global warming.
The density of carbon dioxide in the atmosphere, which was about 280 ppm around 1900, is now 363 ppm and the average temperature of the earth rose by 0.5 centigrade these 100 years. A survey of Carnegie Mellon University surmises that the temperature in the 21st century will rise by 1 to 4 centigrade, though the probability of it rising by more than 4 centigrade is less than 20%.
It was not until recently that the global warming was worried about. In the 1970s scientists was worrying that the earth was rather chilling. The whole history of earth shows that the density of carbon dioxide tends to lower and the earth will enter the next ice age, because these million years have repeated the cycle of ten thousand year long rapid heating and ninety thousand year long slow chilling and this cycle seems to continue from now on.
2. Skepticism on the Agitation
There are diversity of opinions among scientists as to whether it is because of human activities that the global temperature is rising, whether it will go on rising and whether the global warming has an undesirable influence on us. The counterarguments offered by those who doubt the greenhouse effect hypothesis are as follows
2.1. Men are not responsible for the warming
The rise and drop of temperature precedes that of the carbon dioxide density in the atmosphere. This indicates that the rise in temperature has heightened the carbon dioxide density and not reversely. The carbon dioxide density depends on the temperature of the surface water of seas, which depends on changes in insolation (solar heating) brought about by variations in the eccentricity of the earth’s orbit and in the short term by the number of sunspots. The growth in temperature and carbon dioxide density for the last 100 years is therefore not to blame for men.
2.2. The warming is good for living things
During the Mesozoic era, about 245-65 million years ago, when dinosaurs were striding, the carbon dioxide density was ten times as high as that of today and temperature was about ten centigrade higher than today but the earth those days was a paradise for a life. To take a recent example, the temperature in BC6000-3000 was higher than it is today, but meteorologists call this period climatic optimum, which enabled men to start agriculture and civilization. Generally speaking, the higher the temperature and carbon dioxide density gets, the more active plants make their photosynthesis and the better-off animals including men are.
2.3. Air Pollution prevents the warming
How can you explain that the temperature gets higher in the Southern Hemisphere than in the more industrialized Northern Hemisphere, if burning coal and oil heightens the global temperature? The fact is that aerosol produced by combustion of coal or oil including much sulfur reflects part of solar energy and thus chills the earth. If you want to prevent the global warming, you should burn more oil or coal.
3. The essence of the problem
My answer is as follows
3.1. Men are also responsible
Although scientists have explained the change of temperature by means of that of insolation since the Milankovitch theory, the former does not necessarily correspond with the latter. The behavior of climate is typical chaos and we have not found its deterministic rule. Granted that the increase in insolation heightens the temperature, we cannot deny the positive feedback of increased greenhouse effect gases heightening the temperature.
3.2. The warming causes cooling
The growth in temperature and carbon dioxide density itself is not a problem. If carbon dioxide density should exceed 5000 ppm, it will affect human bodies. But we do not need to worry about such an improbable case. The real problem is the rapid rate of change: 0.5 centigrade per 100 year. When it gets rapidly hot, ice in the Polar Regions melts, which in turn decreases surface layer salinity and, as fresh water is less dense than saline water, this freshening reduced water density and slowed the deep water formation process. At the poles, the water is cooled and sinks as a plume to the deep ocean. The depth of the plume used to be 4000 meter but turns out to be only a tenth of the past in the 1990s.
The ocean conveyor belt that sinks in the North Atlantic and along Antarctica, floats to Indian Ocean and Pacific Ocean and gradually returns to the Polar Regions is called thermohaline circulation because it conveys heat and sunken nutrition. This thermohaline circulation will stop and be never restored, if carbon dioxide density increases by 2% or more and reaches 750ppm.
Greenland Ice Core indicates that the Holocene epoch, which began at the end of the last glacial epoch about twelve thousand years ago, experienced an unusually stable climate. It is because of the thermohaline circulation that transfers heat and keep climate stable. If the global ocean circulation should stagnate, it will threaten our civilization. We have a historical evidence for it. When the last ice age ended and the ice caps began to melt, the warming trend reversed and the earth reverted to ice age conditions for a period of 700 years known as the Younger Dryas. The large amount of fresh water would offset the salinity levels around the Northern Atlantic. These new, fresher waters would inhibit the downward circulation of the conveyor belt in this area. Shutting off the conveyor belt entails shutting off the atmospheric trends that accompany the conveyor belt. Thus, Europe would gain no warming winds through the conveyor belt. This would lead to dramatic cooling trends until the runoff became absorbed, incorporated into the oceans and the conveyor belt could begin again. Sudden cooling follows sudden warming. This roller coaster climate change would increase indeterminacy, namely information entropy.
Some scientists suspect that abnormal weather like El Nino has to do with the stagnation of thermohaline circulation. El Nino is a stagnation of ocean and atmosphere circulation. Trenberth analyzed the data in 1882-1995 and pointed out that the long-term El Nino phenomena these days are far larger than the past. As growth of carbon dioxide density stagnates atmosphere as well as ocean circulation, recent abnormal weather might be caused by global warming.
3.3. The warming also increases entropy
We must throw away entropy into environment to maintain our lives and civilizations. The entropy is carried by ocean and atmosphere circulation and finally thrown away into the universe in the form of waste heat. The essential problem of global warming is that, if greenhouse effect gasses go on increasing, we will be not able to discard the waste heat, the last form of garbage, into outer space and this will bring our living world close to a thermal equilibrium.
The problem of sea level rising is a minor one and if you took this problem for an essential problem of global warming, you might agree to burning coal or oil to produce aerosol and thus chill the earth. Although air pollution lowers temperature temporarily, it increases entropy of atmosphere and has a bad influence on environment.
Generally speaking, a rise in temperature heightens thermal entropy but a rise of average global temperature does not mean an increase in global entropy. The average temperature of 1-liter air of 10 centigrade and 1-liter air of 30 centigrade is the same as that of 2-liter air of 20 centigrade. In order to express the essence of the problem, we should substitute "global heat death" for the misleading term "global warming".
What kind of energy should we rely on to prevent global heat death? – That is the theme of the next article.