It is becoming increasingly clear that human activity can impact this tenuous blanket. And in general the consequences of doing so may be too terrible to contemplate. The author believes that the situation has not yet become hopeless. But given the population explosion of human kind, with the attendant growing demand for energy, it appears increasingly imperative that massive changes in how we produce that energy be implemented.

"Homo sapiens" is Latin for "wise man." The next few decades may well determine whether that name is appropriate or tragically misplaced.

A molecule of methane consists of one carbon atom bonded to four hydrogen atoms. Or, since a molecule of carbon is one and the same as a carbon atom, whereas a molecule of hydrogen consists of two hydrogen atoms, a molecule of methane consists of a carbon molecule bonded to two hydrogen molecules. In larger terms, a mole of carbon (6.02 x 10²³ carbon molecules) combines with two moles of hydrogen to form a mole of methane.

Methane is normally a colorless, odorless gas. It is lighter than oxygen and nitrogen and therefore rises if released into the air. Along with other more complex hydrocarbon gases, it is a component of natural gas. Thus it is flammable (and even explosive), and at present is an important source of energy.

Energy is released when methane is oxidized (i.e., when it interacts with oxygen). If the percentage of methane in a methane/oxygen mixture is great enough the process is violent (combustion). In the case of lower percentages the process is much more gradual. But oxidation still occurs and on average a molecule of methane, released into the atmosphere, will oxidize in twelve years.

During the oxidation process, one molecule of methane combines with two molecules of oxygen, producing two molecules of water and a molecule of carbon dioxide. The reaction is exothermic, which is to say heat is released. The oxidation of methane consumes oxygen gas.

At present, methane comprises only .0002% of the Earth’s atmosphere. However, much vaster quantities of methane are locked up in permafrost and deep ocean hydrates.

As oxidation occurs, the oxygen and methane consumed from the atmosphere are replenished by various processes. In the case of oxygen, plants convert carbon dioxide to oxygen during photosynthesis. Atmospheric oxygen, depleted by the oxidation of methane and a host of other substances, is thereby maintained at a steady concentration of 21%. (Most of the remainder of air is nitrogen.) Since fauna (animals) require minimal oxygen concentrations of approximately 18%, the 21% concentration of oxygen fortunately remains remarkably constant.

A historically important source of methane was and continues to be methanogenic bacteria. These bacteria metabolize dead plant matter, producing methane as a byproduct. The geologic evidence suggests that, billions of years ago, the concentration of methane in the atmosphere was considerably higher than it is today.

Vast quantities of methane, so much more prevalent in Earth’s ancient atmosphere, were in time "locked up" in permafrost and oceanic methane hydrate deposits. If methane hydrate is sufficiently warmed, its locked up methane is released, usually into the atmosphere and/or into sea water. It is presently estimated that approximately 3 x 10¹¹ tons of methane are held in permafrost and deep ocean methane hydrate deposits.

The amount of oxygen in the atmosphere is approximately 1.2 x 10¹⁸ tons. But a mole of oxygen weighs twice as much as a mole of methane, and two moles of oxygen are consumed in order to oxidize one mole of methane. It would therefore take a significant percentage of the oxygen in the atmosphere to oxidize all of the methane sequestered in permafrost and oceanic hydrates.

As previously mentioned, the oxidation of methane is an ongoing process. But the depletion of oxygen by this and other processes is presently matched by the production of oxygen by the plants. It is a remarkably robust and stable mechanism for the maintenance of the approximately 21% concentration of oxygen in the atmosphere.

Indications are that recent human activity is impacting this mechanism, and that the percent of oxygen in air may be gradually declining. Two contributing factors to this decline appear to be our ever increasing rate of burning hydrocarbons (including methane) to produce energy, and the deforestation of the planet’s equatorial forests to produce agricultural land.

There are also indications that the biomass of single-celled plants in parts of the oceans is in decline, owing perhaps to global warming, pollution and other factors. (In general oceanic single-celled plants require cooler water. The warmer tropical seas are virtual deserts, in the sense of a near-total absence of such single-celled plants.)

Since the plants’ replenishment of atmospheric oxygen is a gradual process, a sudden drop in oxygen levels would present a grave threat to fauna in both the seas and on dry land. Although such sudden changes would not occur at present rates of hydrocarbon combustion, prudence suggests that steps be taken to produce energy by "greener", non-oxygen-depleting methods. Burning fuels for the production of energy entails an increase in the rate at which carbon dioxide is added to the atmosphere. And carbon dioxide is a greenhouse gas; it tends to prevent solar energy from re-radiating back into space. As in the case of a locked car sitting in sunlight, the air heats up.

There definitely appears to be a warming trend in the atmosphere. If nothing else, such a trend could hasten the release of methane from permafrost. The rapid retreat of glaciers indicates that the process may already be under way.

A rise in atmospheric methane concentration will further increase the rate of global warming, since methane is 21 times more potent as a greenhouse gas than carbon dioxide is. Global warming will in turn warm sea water, and could ultimately result in the relatively sudden release of vast plumes of methane from the ocean depths. Such a release can be expected to quickly reduce the amount of oxygen in seawater, perhaps too rapidly for the dwindling single-celled plants to replenish. Massive extinctions of oceanic fauna could occur.

As oxygen levels fall in the oceans, more and more of the unlocked methane would cross the water/air boundary. Experience on much smaller scales, with the sudden release of methane from disturbed sediments in ponds and lakes, indicates that explosive levels of methane may temporarily accumulate at the water’s surface. In the oceanic case, the prospect of vast pockets of methane being ignited at sea by lightning is truly a daunting one, as it could result in a rapid depletion of atmospheric oxygen.

One of Earth’s greatest catastrophes occurred at the end of the Permian period, long before dinosaurs came upon the scene. It is believed that a staggering 95% or more of all animal species in the seas went suddenly extinct, and similarly for a somewhat smaller percentage of land-based species. In effect, animal life nearly vanished from the planet.

Heat-loving plants, on the other hand, evidently benefited from the same catastrophe. These results are consistent with a sudden drop in atmospheric oxygen levels, accompanied by a sharp rise in carbon dioxide levels. These two events are precisely what might be expected from a sharp increase in the concentration of methane in water and in the air.

For this reason many scientists believe that, perhaps owing to global warming, such a large and sudden release of methane from hydrates occurred at the end of the Permian period. One can envision lightning-induced ignitions of enormous quantities of methane occurring over the oceans, resulting in atmospheric oxygen depletion that overtook the natural replenishment mechanisms. That is, before the plants could push oxygen levels back up to animal life-sustaining levels, the damage would have been done. Similar remarks would apply to oxygen levels in the seas.

Even if such ignitions were rare, or didn’t occur at all, the sudden increase in atmospheric methane would greatly accelerate global warming. Thus searing heat might also have contributed to the great Permian extinction. And, since a byproduct of methane oxidation is water, the amount of water from such oxidation, added to water from melting ice caps, might have greatly increased the amount of water on Earth’s surface. Global flooding of biblical proportions may have occurred.

For many reasons it seems well advised to lessen and hopefully to halt the present rate of global warming. Indeed it may well be a matter of species survival that we produce energy by means that do not entail increased rates of carbon dioxide emission into the atmosphere. Large scale nuclear, photovoltaic, wind and hydroelectric power generation should be implemented without delay. And carbon dioxide-generating technologies, including the burning of ethanol and other hydrocarbons (oil, natural gas, coal, etc.) should be phased out.

There is a noteworthy exception. At present an estimated 20% of methane released into the atmosphere comes from cattle excrement. This number can be expected to increase as human population increases. Since methane is a much more potent greenhouse gas than carbon dioxide, it would be beneficial (a) to capture methane from cattle waste before it is released into the atmosphere, and (b) to burn it, probably in motorized vehicles. An infant but burgeoning industry is now processing cattle waste and capturing the methane that would otherwise be released into the atmosphere.

Following the Permian extinction, Earth must have become a very quiet place for millions of years. It is sobering to think that history could repeat itself … particularly if we could prevent such a repeat simply by changing our methods of generating energy. To reiterate what others have already said, our very survival as a species could hinge upon whether we abandon fire as our primary source of energy. The needed alternative technologies are well developed. And there is ample wealth to implement them on adequate scales.

Whether we do so in time to ward off some very scary scenarios is essentially a matter of reordering our priorities.

http://www.dcn.davis.ca.us/GO/dorritie/

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