Science, Part 27:
Climatology

We covered meteorology in the last two issues of The Alaric Heim Page. This month we'll discuss it's sister field, climatology. Whereas the weather (meteorology) is the instantaneous state of the atmosphere, climate (climatology) is the average weather over some long period of time. A common measure of climate is the climatic normal, which is simply the mathematical average over a 30-year period (generally 3 consecutive decades, making 1961-1990 the most recent normals period).

Climate, like the weather, affects many parts of society. The average weather conditions define the major plant zones and agricultural belts of the world. The study of climatology is important to government and industry planners. Heating fuel companies depend on long-term averages of heating degree days to manage oil and gas supplies. The colder conditions in high mountain areas regularly result in winter snows, on which the ski industry depends. Heavy winter snowpacks melt slowly during the spring in the mountainous western U.S., bringing a steady supply of stream water to agriculture and urban interests.

As in all of the sciences, scientists in the early civilizations had a crude understanding of climate. At about the time of Christ (roughly 10 B.C. to 1 B.C.), the Greek geographer Strabo of Amasya (in present-day Turkey) divided the world into frigid, temperate, and tropic zones. The Roman geographer Mela believed that the torrid zone near the equator was so hot that people cannot cross it to reach the southern temperate zone, in which people totally unknown to the north lived.

1827 - Jean Baptiste Fourier suggests that human activities have an effect on Earth's climate. Debate on these anthropogenic effects heated up in the 1980's when greenhouse warming (global warming) became a major issue.

1840 - Dove first uses the term normal.

1872 - the International Meteorological Committee resolves to limit normals to a uniform period so data collected between stations can be comparable.

1884 - Vladimir Köppen produces a world map of temperature zones. He later expanded his climate classification scheme. Köppen's goal was to relate climate to vegetation but, at the same time, provide an objective, numerical basis for defining climate types in terms of climatic elements (temperature, precipitation, and their seasonal characteristics). His five major climate types are designated with capital letters: A = tropical forest climates which are hot all seasons; B = dry climates; C = warm temperate rainy climates with mild winters; D = cold forest climates with severe winters; and E = polar climates. Seasonal characteristics are identified with lower case letters: a = hot summers; b and c = cool summers; d = very cold winters; f = rainy all year round; s = dry summers; w = dry winters. The southeastern U.S. falls under the Cfa climate type.

After examining geological evidence, von Charpentier (1786), Venetez (1821), and Louis Agassiz (1837) determine that modern-day temperate Europe was once covered by a series of massive ice sheets. Arrhenius (1896) discovers that the amount of carbon dioxide (a greenhouse gas) in the atmosphere determines the global temperature and theorizes that the ice ages occurred because some process had reduced the level of carbon dioxide. Milankovitch (1920) published his astronomical theory of the ice ages, in which he postulated that changes in the earth's orbital geometry (eccentricity of the earth's orbit, precession of the equinoxes, and tilt of the earth's axis) affect the amount of sunlight reaching the surface. Coral growth, ice cores from the polar ice caps, and deep sea cores from the ocean bottom are additional evidence that the earth has undergone at least four major glaciations during the last million years (Pleistocene period) and that the last 10,000 years (the Holocene) have been a warm interglacial. A period of alpine glacial advance occurred during the 13^th to mid-18th centuries, but temperatures have generally warmed during the last 150 years.

References:

Critchfield, H.J., 1974: General Climatology, Third Edition, Prentice-Hall, Englewood Cliffs.

Espenshade, Jr., E.B. & J.L. Morrison (eds.), 1978: Goode's World Atlas, Fifteenth Edition, Rand McNally & Co., Chicago.

Guttman, N.B., 1989: Statistical descriptors of climate, Bulletin of the American Meteorological Society, 70, 602-607.

Hellemans, A. & B. Bunch, 1988: The Timetables of Science, Simon & Schuster, New York.

Schneider, S.H. & R. Londer, 1984: The Coeveolution of Climate & Life, Sierra Club Books, San Francisco.

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