The greenhouse effect and all that. It's not easy deduce climate from weather.
Also consult the end of the article on atmospheric radiation, which has a discussion of this debate.
"Global Warming" is the name for the current environmental cause célèbre whose protagonists are politicians and atmospheric scientists, with a chorus of industrialists, environmental activists, and other rabble with this or that axe to grind. The Kyoto Protocols of 1997 bound its signers to a 5% reduction (7% for the US) in the amount of carbon dioxide released into the atmosphere by 2012, based on 1990 levels. The U.S. has just reneged on the deal, raising a furore. This paper will take a look at the problem from the scientific side, and try to explain what it is all about and what the outcome might be.
First, let's consider the so-called "greenhouse effect," which always crops up, although those who use the term seldom know what it means. In a greenhouse, radiant energy, sunlight, enters the glass walls and is absorbed inside, heating things up. The things inside the greenhouse also radiate energy, but at a longer wavelength than the sunlight, as what is called infrared radiation. Glass is transparent to sunlight, but opaque to infrared, so the energy cannot radiate away easily. The temperature inside the greenhouse then rises, until the losses by convection and conduction through the glass equals the energy coming from the sunlight. This warms the greenhouse nicely, as you know.
The atmosphere is transparent to sunlight, like glass. Nearly all of the dry, pure atmosphere consists of nitrogen (70%), oxygen (29%) and argon (1%) and is just as transparent to infrared as it is to light. The sun shines down and heats up the surface of the earth. However, more complex molecules present in small quantities in the air, such as water vapor, carbon dioxide and methane, absorb and emit infrared radiation and slow down its outward movement through the atmosphere. The effect is like a greenhouse; the earth receives more light than it radiates as infrared until it heats up a little to increase the infrared radiation. When a balance is achieved, the earth is a little warmer--the greenhouse effect.
If you know the concentration of these infrared-active molecules and the structure of the atmosphere, it is a complex but straightforward calculation to find the equilibrium temperature of the earth. Atmospheric scientists are very proud of being able to do this, using computer programs reflecting their best ideas and assumptions. When they assume more and more carbon dioxide, the calculated equilibrium temperature of the earth rises. It seems that recent calculations give a rise between 2.5°F and 10°F by 2100, assuming some rate of release of carbon dioxide. Exactly what this is the temperature rise of is not clearly stated. Also, the fact that these figures are in Fahrenheit is a little curious, as if they were created for a particular audience.
The greenhouse effect is not in doubt--it is real and effective. What is in doubt are the assumptions used in the radiative calculations, and the application made of them. What is needed are some comparisons between such calculations and what is observed, and these comparisons seem to be lacking. With that said, a real increase in the observed temperatures around the globe seems to be established. In fact, observed temperatures must either decrease or increase; it is pretty sure they will not remain constant. Apparently it happens that they are increasing, however poor the definition of "average temperature."
The syllogism is that the temperature is increasing, the greenhouse effect of added carbon dioxide will cause an increase in temperature, the amount of carbon dioxide in the atmosphere is increasing (all true), and therefore the increase in temperature is caused by added carbon dioxide. Not only that, but it is concluded that if the amount of carbon dioxide from burning fuels is reduced, then the temperature of the earth will decrease or stabilize. The conclusion is possible, but not proved in any way. Let's look at some factors that could disturb this specious syllogism.
First, we are in a geological epoch called the Pleistocene, characterized by continental glaciation, that has proceeded for about 1,800,000 years. Yes, the last 10,000 years is called the Holocene, as if all history were only a preparation for the current instant, but if there are geologists 1,000,000 years hence, we will have been assigned to the Pleistocene, and they will rule the Holocene. There have been about four cold glacial periods, and four warm interglacial periods so far in the Pleistocene. If things go as they have been, we are about 1/4 of the way through the fourth interglacial period, 25,000 years in. The earth's temperature is not stable; either it swings quickly to cold and ice, or quickly to hot and sunny. Nobody knows why, how or when. This is very unusual behavior for the earth. The last time anything like this happened was during a time called the Carboniferous, when similar ice ages occurred in the southern continents for a while. Normally, the earth is nice and cosy, with no ice caps or glaciers anywhere. The earth's temperature has been decreasing steadily since the dinosaurs disappeared. A slight increase since 1912 was ascribed to the lack of volcanic eruptions. Considering all this, the only way we could reasonably expect the earth's temperature to go is up.
The previous paragraph may give an inkling that geological time is a good deal different from human time. Humans have evolved and spread thickly over the earth in the Pleistocene, in the last 1 million years of the earth's history of at least 4300 million years. We are now in a time of the greatest extinction of species ever seen; all will happen in a mere flash of time, geologically. The Time author states as if he knew, that the recent rise in global temperature "outstrips anything in the past 100 million years." Nobody has been keeping records that long. This is just a meaningless statement meant to impress, a statistic that no one could possibly know. Human events are on the scale of weather; global warming is on the scale of climate.
The author also asserts that carbon dioxide is "the most abundant heat-trapping gas." It is not, not by a long way. Water is. Water is a very abundant greenhouse gas whose atmospheric concentration varies widely with time and location, unlike carbon dioxide. Water has a great effect on the temperature of the earth, not only as vapor in the atmosphere, but as clouds, precipitation, and, above all, the oceans. Carbon dioxide is not even the most effective greenhouse gas; methane is more effective. Like water, carbon dioxide is essential to life. All of our food comes from water and carbon dioxide, combined by photosynthesis to make carbohydrates and all the other organic compounds.
Carbon dioxide takes part in many chemical and physical processes; most free carbon dioxide is dissolved in the ocean, most combined carbon is in carbonate rocks, limestone and dolomite. All the carbon dioxide was originally in the atmosphere, and oxygen was absent. Life has locked up the carbon dioxide and liberated oxygen, while plants and animals have evolved to live in an oxygen atmosphere with a small carbon dioxide component that is constantly exchanged. No one understands the carbon dioxide cycle quantitatively, and so the prediction of the amount of atmospheric carbon dioxide is difficult if not impossible. Once again, the false syllogism occurs: carbon dioxide in the atmosphere is increasing; burning coal releases carbon dioxide into the atmosphere, therefore burning coal is responsible for the increase in carbon dioxide. Well, perhaps, but it is a long way from certain.
In fact, the burning of any carbon-containing fuel, whether natural gas, coal, oil, wood or dollar bills, releases carbon dioxide. Coal is mainly carbon, so the product of combustion is carbon dioxide. Gasoline is also mainly carbon, and the main product of combustion is again carbon dioxide. Natural gas, CH4 burns to CO2 + 2H2O, producing carbon dioxide and another powerful greenhouse gas, water. Most of the carbon dioxide produced by the United States comes from gasoline, kerosene and diesel fuel, not coal. The Time author states that there is work on "cleaner ways to burn coal." Whatever this may mean, there is no way to reduce the amount of carbon dioxide. All fossil fuels contain impurities, notably sulphur. It is just harder to separate sulphur from solid coal than from gaseous natural gas. In both cases, there are sources largely free of sulphur that are readily available.
The Time author shows his ignorance in claiming that a combined-cycle plant (gas turbine with steam turbine final stage) can approach "90% efficiency." This he gets from a cycle efficiency of 60% (rather doubtful, actually, except in advertising claims) plus using the 30% of the waste heat for heating. Hell, on this basis burning coal in the fireplace is 100% efficient. Efficiency only means that you burn less fuel, of course.
Among the other greenhouse gases is methane, which comes from belching cows, rice paddies, pipeline leaks and other inefficiencies. Methane is not only an effective greenhouse gas, it also disappears rather slowly when it gets into the atmosphere. It is not part of a complex cycle the way carbon dioxide is. There may be methane locked up in gas hydrates in the Arctic that could be released. In fact, methane is a big worry, but since it has nothing much to do with coal, it is pushed into the background.
Suggested controls of climate have been (1) astronomical, (2) atmospheric, (3) oceanic, and (4) magnetic. Astronomical theories are hard to support, since they provide periodic causes, while the effects are not. Variations in the sun's energy flux also have been suggested. It has been noticed that ice ages have begun when the earth's magnetic field reversed in direction, which it does now and then. The link to climate, however, is elusive. Atmospheric or oceanic controls are more likely, but causes are obscure. Except, of course, for the emission of carbon dioxide.
Atmospheric scientists are, naturally, concerned specifically with the atmosphere and know more about it than anyone else, as they will be happy to tell you. Like all modern professional scientists (one cannot speak of individuals, but in the mass the trends are clear) atmospheric scientists know only the atmosphere, and almost nothing else. You probably have heard of El Niño, and its great effect on the weather. This gives some idea that the ocean determines climate, and the ocean is much more massive and powerful than the puny atmosphere, which governs weather. The oceans contain some 270 times more mass than the atmosphere, and are in contact with it over 71% of the earth's surface. That the oceans are the key to the ice ages has been suggested from time to time, and there is no better cause waiting in the wings.
King Canute is reputed to have staged a demonstration to refute his flattering courtiers who called him all-powerful by setting his throne on the beach and commanding the tide to reverse. When his ankles got wet in the surf, he proved his point. The Kyoto Protocol, and everything like it, presumes that its provisions will be effective in reversing global warming. If carbon dioxide really is the problem, it is too feeble to have any effect. If carbon dioxide is not the problem, it will also have no effect. The piddling most that humans can do is probably a long way from controlling geology.
Composed by J. B. Calvert
Created 8 April 2001
Last revised 6 June 2009