by Ken Wear, BSPhys, MSEE
Determining "global temperature" is far from an exact science. While I don't see the published value challenged, that is likely because no one has a better estimate. I have assumed it is determined in this manner: Stations all over the world report what I assume is the average between daily high and low; that value is adjusted for the surface area served by that station, and then a grand average is taken of those values. Arctic regions have fewer stations and are not as well represented in the total. About 3/4 of Earth's surface is ocean and there are no permanent stations there (although there are bouys anchored here and there); however ocean surface temperatures do not change radically around the clock like land temperatures and do give some stability in their contribution to the grand average. Meteorologists are doing the best they can to determine a meaningful global temperature.
People ask me about global warming. While I am scientifically educated, alert and intensely interested in public issues, my opinion is no more than my opinion on an issue that has become charged with partisan politics. Let me cite several pertinent pieces of information; you can assess their impact.
Earth's temperature is a balance between (1) radiant energy produced by the Sun which impinges on our upper atmosphere and is transmitted to the ground and (2) energy radiated from the ground into the atmosphere and thence into space. Incoming energy, because of spectral characterisitics of sunlight and of gases in the atmosphere, is little absorbed in the atmosphere, most of it striking ground cover and the ground, where it is divided between absorption and reflection back into the atmosphere. Outgoing energy is partly absorbed by the atmosphere and the rest transmitted into space. Energy in the atmosphere may be divided between cloud cover, air temperature, etc., and is either radiated into space or returned to the ground. Radiation from a source has been found to be proportional to the fourth power of absolute temperature; equating energy radiated by our Sun to energy radiated by Earth produces a temperature for Earth of zero degrees F. But our average temperature is 59F, which has in the past been determined by natural processes without any influence by man. So the natural greenhouse effect of Earth's atmosphere has made our planet habitable.
Earth has been through temperature swings in its past. During the last million years there were several ice ages, the last ending some 10-12,000 years ago; there have been lesser variations lasting decades to centuries, these with scarcely any impact by man. In the 1950s there was concern Earth was entering a cooling period; present concern is that Earth is entering a warming period. Do the activities of man have an impact on average global temperature? We cannot question that we do, but we can question how much and, if we conclude our contribution is significant, we can begin to explore reasons. And, once we arrive at reasons, we can undertake to minimize our impact. Do we need to be concerned?
During a deep ice age ocean levels drop because the water is bound up in glaciers, and I have no doubt saline content of the oceans is significantly increased. And there is presently enough water bound up in the Arctic and Antarctic to raise ocean levels several feet if it all melted. In fact, migration from Asia to America undoubtedly took advantage of a plateau south of Alaska exposed by lower ocean levels during glacial build-up. I have heard nothing about advancing and retreating deserts but note that the horn of Africa has experienced extended draught because the prevailing winds have shifted. And our food supply, notably agriculture, is strongly affected by moisture.
The greenhouse effect results from spectral characteristics of the gases where nearly all are transparent to ultraviolet and higher frequencies, but in the infrared there are absorption lines and bands. Sunlight incident on the upper atmosphere is at the higher frequencies so the atmosphere absorbs little energy (except ozone intercepts ultraviolet); what is not reflected back into space heats Earth, which in turn emits radiant energy at infrared frequencies (because of its lower temperature). The atmosphere does not retain energy but re-emits it, partly back to Earth. Water vapor is some 1.0-4.0% of the air, while carbon dioxide now represents some 400 parts per million (which has increased some 30-35% since the beginning of the industrial revolution).
Of the greenhouse gases, water is dominant (as humidity, not as clouds), accounting (with significant variation) for about half of the total effect, while carbon dioxide accounts for about 18%, methane about 5% and a number of other gases accounting for the balance. The greenhouse gas attracting the most attention is carbon dioxide; while water vapor and methane have a greater effect while present, concern for carbon dioxide centers on its longevity in the atmosphere, which is expressed as decades-to-centuries. There are tremendous quantities of methane bound up in permafrost, and one effect of rising average temperature in the Arctic regions is melting of permafrost and the consequent release of methane. I have heard of no concern for the increased methane content of our atmosphere. Some decades ago forests in New England were dying due to acid in the air from industrial smokestacks and carried by the trade winds, producing acid rain. Emissions were reduced and publicity about the health of New England forests has ceased. We hear nothing about sulfur subliming from sulfur mines into the air; I have no doubt that sulfuric acid in the air will increase with temperature as the rate of sublimation increases; the planet Venus was likely inhabited at some time in the distant past, but the present sulfuric acid content of its atmosphere precludes life.
In looking to remedies for greenhouse gases in our atmosphere, we should first look at what activities most contribute. The estimate is: greenhouse gases result 21% from power stations, 17% from industrial processes, 14% from transportation, 13% from agriculture, 11% from fossil fuel processing (oil, coal, methane) and lesser proportions from other sources.
Public debate has rarely mentioned the direct release of waste heat from consumption of coal and oil in the generation of electricity or the heat rejected from various processes such as manufacture or transportation. These must surely add to the energy that must be radiated from Earth into the atmosphere and thence into space. One of the most wasteful processes of modernity is production of electricity remote from users, so 60+% of input energy is rejected into the air or into waterways as waste; smaller generating facilities located in the midst of users of heat would both reduce heat rejected as waste and provide a portion of the heat users now derive from other sources with their consequent production of more greenhouse gases.
There is a direct tie-in with greenhouse gases and uses of petroleum since heat from using petroluem products and carbon dioxide from their combustion both make their way into the heat balance of the planet. Of course, combustion of coal and methane also produce waste heat and carbon dioxide. To the extent consumption of petroleum is replaced by consumption of coal and methane, there is little advantage in production of greenhouse gases, so replacement of one fossil fuel by another fossil fuel has little effect on man's contribution to global temperature.
If you linked here from the essay on energy, your BACK button should return you to the essay.