by Ken Wear, BSPhysics, MSEE
Average global temperature is a contrived number taking into account variations in temperature from the poles to the equator; it is at best an imprecise number reflecting an informed scientific estimate. It may be subject to challenge and acceptance is likely because no one has a better estimate. Orbital satellite data is no doubt corroborated by ground-based data from around the world. And projections into the future involve looking back into the past at variations in ice cores, coral reefs, tree rings or thermometer data, each with its own dependence on the time span embraced by our knowledge. Climate scientists are doing the best they can. There can be no question mankind's activities have an impact; today's question is whether that impact is significant.
People ask me about global warming. While I am scientifically educated and intensely interested in public issues, my opinion is no more than my opinion on an issue that has become charged with partisan politics. In researching the topic of contribution by atmospheric gases to surface temperature, I have been concerned that sources and sinks of pertinent gases have not been adequately explored and if we now have a complete catalog of processes that contribute (or absorb) significant quantities of relevant gases. Let me cite several pertinent pieces of information; you can assess their impact.
What is average global temperature? With winter in the southern hemisphere when it is summer in the north, with ups and downs in temperature weekly with weather, with variation throughout the day and night, the reported average global temperature is an average of composites. I recognize two alternate ways to attempt a measurement, one historically-used methods and one based on orbital satellites. Our romance with space-age equipment suggests the latter although that must be consistent with ground-based data..
(1) Stations all over the world measure air temperature at the surface and report their measurements, likely using 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 so their contribution does give some stability to the grand average.
(2) A series of orbital satellites measure surface temperature based on radiation received from a relatively unobstructed view of the surface; that is of course a local temperature but can be integrated over the entire orbit and a series of orbits integrated over the entire earth. Influence of cloud cover and atmospheric gases must be taken into account in the reduction of data using those measurements.
There have been efforts to corroborate trends in "average global temperature" by using data from glacial ice cores (extending from the last total melt some million years ago), coral reefs (and I have no information on life times of reefs), tree rings (depending on tree life, with the bristlecone pine reaching back 5-6000 years), and fossils recovered from sediments dated by the same methods used for the animal bones they contain) and thermometers (since their invention 4-500 years ago).
Due to the fourth power law of radiated energy, equating energy from the sun to energy from the ground produces a ground temperature of 0oF. Our average temperature is 59oF, which results from the natural greenhouse effect of Earth's atmosphere; that is why Earth is habitable. I note that the ice point is 32oF, about half way between those extremes of 0oF and 59oF. (And that midpoint is likely why the behavior of water is a crucial element in evolution as well as the primary determinant in producing either cooling or warming trends that lead to formation or melting of ice.)
Since snow and ice reflect more of the sun's energy than forests and plains, a thin blanket of ice or snow triggers a surface temperature drop that encourages the build up of more ice; without a countervailing warming trend Earth becomes shrouded with a blanket of ice. But the green of forests and grasslands absorbs solar energy, which lends to warming; with the ice cover substantially melted the warming trend prevails until build up of ice is triggered to initiate cooling. Hence in Earth's geologic history there have been events massive enough to initiate build-up of ice during a warm period or cause melting of the ice cover of a glacial epoch.
Each gas in the atmosphere has a characteristic spectral dependence; that is, when transparency to specific wave lengths of infrared, visible and ultraviolet energy are measured, each gas has characteristic windows at certain colors (or frequency or wave lengths, however data is plotted) through which radiation is readily transmitted. There are therefore bands of frequencies where energy is absorbed by that gas. As a general statement, nearly all gases are transparent to sunlight, but at the lower energies of infrared there are absorption bands.
Energy in the atmosphere may be divided between cloud cover, humidity, air temperature, etc., and is radiated either into space or returned to the ground by radiation or precipitation. Energy incident on the top of our atmosphere and transmitted to the ground is divided between absorption at the ground and reflection back into the atmosphere. Outgoing energy is either absorbed in the atmosphere, radiated into space or returned to the ground. It is the limited capacity of the atmosphere to store energy that creates the "Greenhouse effect" by preventing transmission to space of frequencies (energy) in those absorption bands.
Of the greenhouse gases, water vapor (1.0-4.0% of the air) has the greater effect (as humidity, not as clouds), accounting (with significant variation) for about half of the total effect, while carbon dioxide accounts (some 400 parts per million, which has increased 30-35% since the beginning of the industrial revolution) 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. Little attention has been given to the immense quantities of methane stored in permafrost covering vast areas of arctic land, which is, in extensive areas, within a degree or two of melting.
What becomes of the greenhouse gases? Of course water is recycled in precipitation although some becomes dissociated and the lighter hydrogen rises to become lost to space. Carbon dioxide in the lower atmosphere takes part in various exchanges such as being absorbed in sea water to increase its acidity or being used by plants (both marine and terrestrial) in their photosynthesis into organic compounds such as food. As it rises into the stratosphere it is subject to normal mixing of gases although there is no mechanism to decrease its concentration. Since there is little thermal convection in the stratosphere and absorption of solar heat by carbon dioxide causes it to rise, it becomes trapped and remains in the atmosphere for extended times. Knowledge of methane is sparse, but it does not take part in exchanges such as photosynthesis; apparently it is slowly oxidized into water and carbon dioxide; while it remains as methane it is some 22 times as effective in trapping solar heat as carbon dioxide.
Earth's surface temperature is also affected by the heat from Earth's molten core as it gradually by conduction reaches the surface. It is thought that radioactivity in the core (which must diminish over geologic time) maintains the core temperature. It is estimated that heat percolating to Earth's surface from its core is some three times the quantity of heat produced by the total of man's activities.
But materials shrink as they cool. The gradual loss of heat, even a minute fraction of one degree, causes pressure on that incompressible core to force magma upward toward the surface, where it collects until the tensile strength of the ground above it can no longer contain the pressure and a volcano erupts.
The balance of natural forces leads me to the conclusion that a warming trend at Earth's surface is natural, but it has been interrupted from time to time by the effects of massive volcanic eruptions. Others insist that sun spot activity varies the quantity of solar energy emanating from our sun and therefore the quantity incident on Earth's atmosphere; no doubt that also affects the balance of energy at Earth's surface but we have no data on variations in sun spot activity over the ages. I cannot speculate on which effect is dominant but it is obvious that Earth's surface temperature represents a fine balance between competing effects.
I have examined temperature readings derived from glacial ice cores. Speculation on mechanism for changing warming to cooling, or cooling to warming, was not presented, but I note the extended intervals of either trend. (There has been discussion of correlation of sun spot activity with climate, and sun spot activity has been recorded in cycles of decades and longer; I am unaware of a correlation.)
Ice core data shows a succession of glacial epochs, each ended with a warming trend that caused ice to melt more rapidly than new ice formed. During successive seasons compaction of snow into ice causes strata in the ice that makes possible determination of passage of years, comparable yearly growth of tree rings. A graph of temperature versus time shows long-term warm and cold periods with time intervals of thousands of years from a deep ice age to the peak of a warm period and tens of thousands of years from peak warmth to the depth of an ice age. But the graph is extremely ragged with periods of gradual warming or cooling measured in centuries; a decade warm-up or cool-down hardly shows at all.
The most recent glacial epoch ended some 12,000 years ago as an explosion in the human population spread on the surface uncovered as the ice retreated. Thinking in the long term, we cannot know if the natural warming trend has reached its peak, moreover, I suspect (since I have no data) man's cities and loss of natural ground cover have increased the absorptivity of solar heat from the green that previously prevailed. Man's developmental activities may well be reinforcing the natural warming trend and possibly have a greater influence than greenhouse gases.
The recurring glacial epochs suggest a sequence where a natural warming trend is occasionally interrupted by an event that hinders solar energy from reaching the ground long enough to initiate a massive ground cover of snow and ice, then the growth of ice cover is interrupted by an event that increases absorption of solar energy that reaches the ground. Thus the advancing or retreating ice cover represents a fine balance between surface reflectivity and atmospheric absorption of solar energy.
During a deep ice age ocean levels dropped because the water was bound up in glaciers, and I have no doubt saline content of the oceans was increased significantly; evidently there is a limit to ice build-up as the oceans are depleted. And there is presently enough water bound up in the Arctic and Antarctic to raise ocean levels many 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 drought because the prevailing winds have shifted. And our food supply, notably agriculture, is strongly affected by moisture.
Super-volcanoes such as Mt. Pinatubo in the Philippines cause, because of the volume of ejected material, severe atmospheric effects. The Tunguska event in Siberia in 1908 laid waste to forests for hundreds of miles but did not produce blast effects that radiated beyond that. I recall the eruption of Mt. St. Helens in Oregon, which covered the state in ash and deposited ash as far east as Georgia. While a massive eruption may cause a global temperature drop, its ash may cover ice with a blackened layer that absorbs the sun's energy. It strikes me that super-volcanoes may have produced the triggers for glacial epochs as well as the warming trends that ended glacial periods.
There are tremendous quantities of methane bound up in permafrost near the surface and even greater quantities in frozen hydrates of methane underneath lakes and oceans, and one effect of rising average temperature in the Arctic regions is melting of permafrost and the consequent release of methane. Until recently I had heard of no concern for the increased methane content of our atmosphere and, apparently, only recently have observations begun to track methane releases. Surface Siberian permafrost may melt in the summertime, and hydrates near the northern Norwegian coast have produced gases bubbling to the surface. 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 sulfur 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 the 1950s there was concern Earth was entering a cooling period; present concern is that Earth is entering a warming period. Did the activities of man change that cooling trend to a warming trend?
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 although methane contributes roughly half the carbon dioxide from coal for the same energy release. 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.
Public debate never mentions heat that is beneficially used in industry and to heat our homes; of course, this heat adds to the total that ultimately finds its way into the environment. 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, where some 60+% of the energy content of the fuel burned to produce electricity is rejected into the air or into waterways as waste; of the remaining 40% some 8-10% is lost to transmission from generators to consumers. 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. Considering efficiency in our use of electricity, it seems likely that at best some 20% of the energy content of the fuel burned to generate electricity is ultimately turned into useful work. Placing generation close to the users has a potential to improve over-all efficiency to perhaps 50% and using (presently wasted) heat in growing selected algae for food or fuel can improve efficiency even more.
(I have just examined temperature data from a single station in Australia, at the Darwin airport. Equipment is upgraded, moved to better or less sheltered areas, recalibrated, etc., and data "homogenized" (which has led to markedly different reported values) in an effort to adjust for the various changes in equipment, location, etc. On the larger picture stations are added, discontinued, etc. It is the homogenized data taken from the totality of stations that is then used in calculating local, regional or global averages, which can then be graphed to show variations over the years and decades of record keeping. What little confidence I had in interpreting reported average global temperature has been undermined, even without the CRU fiasco.)
It is unfortunate that scientists have made a mockery of the scientific process, thus undermining public confidence in the pronouncements of all scientists in all fields where there might be prejudice, agenda or selfish motive. In the field of global temperature there stands before us the question if some semblance of data accumulation can be repeated by calling on the various sources that had contributed data to CRU; I assume from what I have heard thus far that many source records have been destroyed because of the (false) confidence that was placed in CRU. Whatever betide, prudence suggests we await some degree of restoration in confidence in global temperature data before undertaking possibly ruinous economic remedy.
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Fossil fuels store solar energy from past eons, and Earth's temperature is a balance between energy broadcast from Earth into space and energy currently received from the Sun (plus release by man's activities). Our Sun sends electromagnetic energy in all colors from far infrared through visible and ultraviolet. The gases that make up our atmosphere transmit most incident sunlight except for certain infrared color bands. Because of its lower temperature Earth broadcasts only at lower infrared colors so those color bands inhibit transmission of energy into space. Incoming energy is divided between absorption at the ground and reflection back into the atmosphere but outgoing energy is partly absorbed in the atmosphere and a portion of that returned to the ground, creating the "Greenhouse effect" by trapping energy in those color bands. Due to the fourth power law of radiated energy, equating energy from the sun to energy from the ground produces a ground temperature of 0oF; but our average temperature is 59oF, produced by the natural greenhouse effect of Earth's atmosphere; that is why Earth is habitable.
The most reliable estimate of variations in Earth's temperature over geologic time comes from ice core data. That shows long-term warm and cold periods with time intervals of thousands of years from a deep ice age to the peak of a warm period and tens of thousands of years from peak warmth to the depth of an ice age. But a graph of temperatures is extremely ragged with periods of gradual warming or cooling measured in centuries; a decade warm-up or cool-down hardly shows at all. (For a more complete discussion, visit www.rationallink.org/glotemp.htm on the web.) In the 1950s it was thought Earth was entering a cooling period; now it is felt that we are entering a warming period. It is true that man's influence is increasing, but should we interpret a 2-3 year record as reflecting a long-term trend?
The recent disclosure that scientists charged with maintaining global temperature records have decided to make a mockery of science by destroying data contrary to their interpretations is very damaging to public confidence in the pronouncements of scientists in all fields. It is unfortunate, but we can't let the malfeasance of a few destroy confidence in the many; it reminds us anew that each of us must of necessity rely on his own ability to absorb information and reach the best conclusions he can. We can hope the head-long plunge toward legally binding restrictions will be arrested until some semblance of data accumulation and confidence in its correctness can be restored.