We have examined the basic factors which make up atmospheric conditions, i.e., weather, in the troposphere: temperature, air pressure, wind, cloudiness and precipitation. We will conclude our survey of the atmosphere with a consideration of climate. The term weather is restricted to conditions over short periods of time; conditions over long periods are referred to as climate. An example of weather would be rain in an area for a day or two. Climate would be demonstrated by a desert. The weather might change in a desert - a day of rain - but the climate of the desert remains the same. We know, however, that climate has changed during the life of our planet, with complete and total impact upon all life forms. Evidence is growing that the climate zones are now changing, and it is imperative to our survival that we understand why.

Theories of Climactic Change

The astronomer and physicist Galileo observed sunspots - massive eruptions of radiation from the sun - and noted that they disappeared and then reappeared, leading to his theory that sunspots had an effect on the earth's climate. Statistical information now available to us does not show a real correlation between the duration of sunspots and warming of the earth. The data is too new and time is needed to make a final conclusion. This is the first of five theories scientists believe have caused climatic changes in the earth's atmosphere.

A second theory of climatic change is tectonic activity. We described at the beginning of our discussion the formation of our planet and atmosphere, and certainly the earth's climate underwent huge changes in the process. Some scientists theorize that the earth's land masses were at one time all connected. Called Pangaea, this super continent was eventually broken apart by glaciation. The smaller continents moved toward the equator, causing a warming of these land masses. Ice ages resulted in the formation of the earth's largest mountain ranges. The building of mountains and continental drifting takes millions of years, suggesting that climatic change on the earth requires long periods of time.

That the earth's orbit may be responsible for climatic changes is a third theory. There are three types of orbital changes. The first is the shape of the earth's orbit around the sun. This shape changes about once every 100,000 years. This is called eccentricity. The second explanation is based on the fact that the earth tilts 23.5 degrees on its axis with respect to its orbit around the sun. The tilt oscillates, or moves, about 1.5 degrees about once every 41,000. The last explanation is that the earth's axis is now pointing at the north star. It circles the star as if it were a wobbling like a toy top. This movement around the north star is called precession and happens every 23,000 years. From what we have learned, it seems reasonable to accept that climactic change would result from a variation in our orbit. Again, such changes are very gradual.

A fourth theory of climatic change is catastrophic events. One can look back to the age of the dinosaurs and read all the theories as to why all plant and animal life vanished from the earth. What we know of them can be found in their fossils. They really don't tell us much as to why they disappeared 65 million years ago. In 1977, Walter and Luis Alveraz had two theories. The first is that a giant meteorite struck the earth. Upon impact the meteorite vaporized and tremendous fires were started. The rock around the impact also vaporized, sending soot from the vaporization and ash from the fire into the atmosphere. Once in the upper atmosphere, the winds were able to spread this soot around the earth. The dust particles created a dark cloud that prevented the sunlight passing through the cloud. This in turn caused a cooling of the earth which froze the waters, killed the plants, and caused animals to starve to death. The Alvarez's second idea is somewhat related to the first, but a different catastrophe took place. A large volcano erupted into the upper atmosphere. This volcano erupted numerous times sending volcanic ash into the atmosphere where it was able to ride in the upper winds, spreading the ash around the earth with the same results.

These culprits - the sun, the earth's orbit, gigantic meteors, volcanic eruptions - we can do nothing about. We must accept that natural catastrophe is a possibility, and reassure ourselves that in the course of 5 billion years our odds against such an event happening are exceptionally good. But we have a new villain to worry about today, destroying nature's order and upsetting the delicate balance. This latest threat, suspected to be the primary cause of climactic change today, is humankind.

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Last modified: Wed Jul 2 12:06:21 PDT 1997

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