Sunday, June 23, 2019

The Cooling Period of the Holocene

I often comment on the Holocene period and how we are in its cold phase. This is a succinct summary of those comments:

About 11,700 years ago the last 100,000-year glacial period ended, as did the four preceding it in the past half-million years. A 15,000 to 20,000 year interglacial period followed each glacial period, and each of these short interglacials had temperatures about 2 degrees Celsius higher that now plus higher sea levels, and we are presently in the cooling phase of our Holocene interglacial. 

There have been four warmer periods than now in the past 10,000 years. The earliest and warmest, the Holocene Climate Optimum, peaked 6,000 year ago, and was followed by successively cooler warm periods, the Minoan, Roman, Medieval, and our relatively cool present warm period. During the past 6,000 years temperature and sea level have ratcheted down and we just emerged from the coldest period of the past 10,000 years, the Little Ice Age. 

Since 1700AD global temperature has risen 2 degrees Celsius with relatively low levels of atmospheric CO2 (280ppm). As in the four previous periods of warming, atmospheric levels of CO2 played no discernible role in causing their warming or preventing periodic cooling. 

All of these climate changes occurred without benefit of human contributions, just as our present warming period was already 250 years along before human burning of fossil fuels after 1950AD caused a significant increase in CO2 levels. Of interest, the first period of rapid CO2 increase, 1950 to 1980, featured significant cooling from the very warm 1930 to 1950 period, and caused a Global Cooling panic. Over half the warming after 1980 has been a recovery from the drop in temperature 1950 to 1980. 

What can we do about current warming? Take advantage of it like our ancestors did. Civilization began and advanced rapidly during the rapid warming following the Ice Age. It's a good thing our ancestors didn't figure out a way to stop Global Warming then or we would still have mile-thick ice sheets covering all of Canada and a third of the US.!

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