Earth Getting Back To What It Sort Of Used To Be

by Professor Reid A. Bryson

Remember Otzi, the Ice Man? The fellow that was found in the mountains between Austria and Italy a few years ago? He had been shot a little over 5000 climatesci.colorado.edu ago the snow melted back enough for Otzi to be found. Between his burial under snow and his exhumation by nature there was more snow and ice than before, or now. Are we just getting back to what the snow climate used to be?
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One of the well known climatic episodes (to well-educated climatologists) is the Little Ice Age. The hemispheric cooling started in the 1400s, really got going about 1570 (see Frobisher’s journal) and was full-blown by mid-1600s. The Pilgrims picked a lousy time to come to America. After a little amelioration, things got worse culminating in the “Year Without a Summer”. Since then the hemispheric temperature has risen, and we even have thermometers to attest to it. Gee, getting back to what it used to be sure doesn’t sound like the sky is falling and catastrophe looms. Besides, warmer weather reduces the Climatic Overhead and we get more income per unit of energy used.

Incidentally, this sequence can be modeled without even referring to anthropogenic carbon dioxide.

The Northern Hemisphere temperature history as modeled using Milankovitch variations in solar radiation modulated by volcanic aerosols, using oceans and carbon dioxide only as minor dependent variables. BP means before 1955 CE.

This figure captures very well, the “little ice age”, the Medieval Warm Period, and other known variations of late BCE and early CE times. The drivers of this model are Milankovitch calculations (average for the entire Hemisphere) and the observed volcanic record described above. Carbon dioxide is treated as a very minor dependent variable. It is unlikely that a general circulation model which assumes a major role of carbon dioxide can duplicate this known climatic sequence.