Guest post by Dr. Don J. Easterbrook, Emeritus Professor at Western Washington University
Two hundred years ago, Charles Lyell coined the phrase “The present is the key to the past.” In today’s highly contentious issues of global climate change, we might well add “The past is the key to the future, i.e., to forecast future geologic events, we must understand past climate changes. This paper documents past global climate changes in the geologic and historic past.
Recent laser imaging of the Earth’s surface provides new evidence for abrupt, fluctuating, warm and cool climatic episodes that could not have been caused by changes in atmospheric CO2. In a paper presented at the national meeting of the Geological Society of America in Portland, OR, Professor Don J. Easterbrook, Professor of Geology at Western Washington University, presented new data from airborne laser imagery showing well-defined, previously unknown, multiple moraines deposited by glaciers 11,700 to 10,250 years ago.
At least 9 significant, abrupt periods of warming that resulted in retreat of the Cordilleran Ice Sheet are documented by moraines from successive glacial retreats in the Fraser Lowland of NW Washington l(Fig. 1). In addition, smaller multiple glacier recessions are found within the more prominent episodes of glacier retreat. As indicated by the amount of glacier recession between each of the successive moraines, the warming events were of greater magnitude than those observed in recent centuries.
Figure 1. Successive terminal moraines from short–term glacier recessions caused by climatic warming between 11,700 and 10,250 years ago.