You cannot look at climate in 50-, 100- or even 1,000-year terms. For example, between 900 and 1300 A.D., the earth experienced what science calls the Medieval Warming, when average global temperatures nearly matched current levels. There were no cars or Pam spray cans then, and far fewer people.
Three factors combine to make global climate vary widely over time.
First, the sun cycles through maximum and minimum periods where its energy output varies considerably. As a general rule, the more sunspots you see, the busier our star is. Coincidentally, we are entering a solar maximum period now. Whatever we do about carbon dioxide in the atmosphere, it’s going to get warmer.
The second factor relates to three distinct motions of the earth as it spins in orbit. Orbital eccentricity refers to 400,000-year cycles when the earth’s path around the sun is more or less elliptical, which puts us closer or father away at times. Axial tilt describes how the two hemispheres angle toward or away from the sun. Precession is our top-like wobble as the planet spins.
Those three variations in the angles, orbits and positions of our planet in relation to the sun make up what are called Milankovitch cycles, which tend to coincide with periods that alternate between glaciations and warming trends. The earth is currently in an interglacial period, roughly 12,500 years after the last glacial incursion and perhaps 50,000 years away from the next one.
The third factor is the composition of the atmosphere, which lets in or keeps out varying degrees of warmth. Carbon dioxide is known to retain the sun’s heat, and a good thing, too. Without it we’d be an earthsicle. Carbon dioxide is also central to the photosynthetic process. The question is: How much is too much? Obviously there is too much right now, but it is unlikely to “threaten all life on the planet” as Meyers claims.
Climate is immensely complex, and declarations of “This is the cause!” or “That ain’t the cause!” are erroneous. Science is just beginning to figure all this out.
—Mike Brake, Oklahoma City
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