Del Nord’s (“It’s not natural factors,” Dec. 23) story begins in 1880, shortly after the end of the Little Ice Age. Since 1900 there has been general Earth warming coincident with increased anthropogenic greenhouse gas emissions. Yes; this warming can be partially blamed on humans. But climate science is far more complex, and the three-decade cold period from the 1940s to the 1970s remains unexplained. Like many of my geologist colleagues, I believe that longer time periods must be evaluated.

Twenty thousand years ago, when much of Earth was blanketed by ice, what is now Chicago was buried under more than a one-kilometer thickness of it. Since that time, these great ice masses have receded all the way back to the polar regions, a continuing process. Also, during this time the 400-year Medieval Warming period was followed by the above cited 500-year Little Ice Age.

What caused these extreme climate events? Ice core studies tell us that during this whole period atmospheric carbon dioxide levels remained under 285 parts per million. The causes had to be natural forces, such as variation in orientation of Earth’s axis, volcanic activity, and the relationships between cosmic radiation and solar activity.

A principal axiom of geology and cosmology is “History Repeats Itself.” So please, Del Nord, forgive me for believing that natural forces have not suddenly disappeared, and might still play some role in climate change. In regard to a human caused mass extinction: a pseudo-scientific fable.

M. A. Kaufman

Spokane Valley