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Greenhouse in the Past

Long ice cores and oceanic records suggest that there may have been as many as eight rapid cooling episodes in the past 730,000 years, and sharp reductions in the Atlantic conveyer belt - a phenomenon that may well be on our horizon. The changes that we make to the earth today can lead to dramatic changes to our planet.

The Earth's climate is essentially unstable, with very significant changes from warm to freezing. Such rapid changes suggest that climate is sensitive to many factors. As can be seen from the blue line, temperatures have been less variable during the last 10,000 years, by less than 1°C.

Eocene Warming

This warming of 55 million years ago emerged more quickly than geological records can show (beyond the left of this chart). It set in motion a host of important changes around the globe, including a mass extinction of much marine life and raised global temperatures some 15°C. Fossil records indicate key migrations of terrestrial mammal species during this time and evidence for the first horses and primates.

The Younger Dryas

About 12,700 years ago there was another collapse of the thermohaline circulation, producing the huge cooling of at least 27 degrees Fahrenheit in Greenland, lasting 1,300 years. It happened in a series of steps of around 5 degrees. While this event caused icebergs as far south as Portugal, a similar event would be more severe today in our densely populated society.

It is the more recent periods of cooling that appear to be intimately connected with changes to civilization, unrest, inhabitability of once desirable land, and even the demise of certain populations.

The Cooling Event 8,200 Years Ago

Ice cores from Greenland indicate a sudden cooling 8,200 years ago. It immediately following an extended period of warming, much like the phase we are in today. Temperatures in Greenland dropped 5 to 9 degrees Fahrenheit. At this time severe winters in Europe and some other areas caused glaciers to advance, rivers to freeze, and agricultural lands to be less productive. The evidence suggests that the cooling may have been caused by a collapse of the Atlantic conveyor belt. This change from hot to cold occurred a decade or less.

This may have caused the decline of the societies that built many of the stone monuments like Carnac, and perhaps the Sphinx if it is as old as some say.

The Little Ice Age

Beginning in the 14th century after the huge loss of population from the Black Death, the North Atlantic cooled until the mid-19th century. This period brought severe winters, sudden climatic shifts, and profound agricultural, economic, and political impacts to Europe. It was marked by persistent crop failures, famine, disease, and population migration, perhaps most dramatically felt by the Norsemen. Famine caused tens of thousands of deaths.

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