by William Logan

Created on: November 12, 2009

Early research on the "greenhouse effect" started in the late 19th century with work by Joseph Fourier. The further study and subsequent understanding and description of the process has enabled scientists to understand our current climactic warming trend, and hopefully, provide enough advance notice and warning to head off serious climate problems in the future.

As the Earth receives a constant supply of energy from the sun, the shorter wavelength energy easily penetrates the atmosphere and is either reflected back into space by things like glaciers, or absorbed by the Earth's surface. The surface radiates this energy back towards space but with longer wavelengths. Carbon dioxide, methane, and other heat trapping gasses absorb longer wavelength radiation and reradiate some of the energy they absorb back toward the Earths surface, warming the planet. Without this, the earth would be about 70 degrees colder than it is. By comparison, a drop in aggregate temperatures of around 7 degrees caused the Great Ice Age. Venus, the closest planet to the Earth, has an atmosphere that is almost entirely made up of CO2 and methane, and surface temperatures reach 900 degrees as a result.

The concentrations of CO2 in the Earth's atmosphere have varied considerably over the millennia, from around 180 ppm during cold, glacial times to around 300 ppm during warmer interglacial periods. In the twentieth century, however, concentrations have risen well above these levels and done so very rapidly. In preindustrial times there was around 280 ppm CO2 in the atmosphere, now the level has reached 370 ppm and climbing. A graph of global aggregate temperatures during the same period shows them following greenhouse gas concentrations, almost step for step, with the fastest rise in the last twenty years.

In addition to changing the concentrations of heat trapping gasses, there are two other factors that can affect climate temperatures. First, changes in the total amount of energy reaching the Earth. This has had some affect on climates in the past, but the total variation is relatively small, about .1% over an 11 year cycle. This does not appear to be a factor in current warming as we are in a period of very low sunspot activity, though it would be expected to increase in the near future. Secondly, is to change the reflectivity, or albedo, of the surface of the Earth. This can be brought about by a loss of ice sheet as glaciers recede. We are experiencing this on a global scale, and

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