From the Archives: Déjà Vu All Over Again – Climate Change

The consensus in the places that I hang out, in real life and on line, is that it is unseasonably cold and we are sick of it. It reminded of this blog post, which I wrote in February, 2014, when we were also sick of winter in these part.

Earlier this week I stood in a line that moved very slowly. As we waited, people began to tell weather stories–the natural consequence of five weeks of alternating snow and deep freeze. At first the stories focused on the efforts individuals had made to be in that line when the ticket office opened for a once a year event: digging out cars, walking through two feet of snow on un-shovelled sidewalks, etc. Then people moved on to tales of their experiences of the Big Chicago Snowstorm in 1967, or 1979, or 1999.

Just as I got to the head of the line, the snow began to fall again. A collective grumbling broke out. Then a voice from the back of the line said, “You know, winter used to always be like this.”

Whether that’s true depends on how you define “always”.

Over the life of our planet, glaciers have expanded and contracted more than twenty times at intervals of roughly a hundred thousand years, caused by tiny changes in the way the earth moves. “Brief” periods of interglacial warming* were followed by long periods of cold when ice covered the planet. Even those periods of warmth aren’t stable. In the most recent warm spell, following the Great Ice Age, we’ve experienced a number of dramatic climate changes, including:

The Medieval Warming Period

From roughly 800 to 1200 CE, Europeans enjoyed mild winters, long summers and good harvests. Warm centuries in Europe brought problems in other regions. Higher temperatures and changes in rainfall patterns created extended periods of drought in Central America, Central Asia, and South East Asia.

Cultural changes followed climate change. On the plus side: more stable food supplies help Europe take the first steps out of the “dark ages”,** favorable ice conditions allowed the Norse to travel pretty much everywhere, and reduced grazing land helped Genghis Khan to pull the Mongolian tribes together into an empire. On the down side: drought contributed to the end of the Chaco Canyon culture of modern New Mexico and Angkor Wat, favorable ice conditions allowed the Norse to travel pretty much everywhere, and reduced grazing land helped Genghis Khan to pull the Mongolian tribes together into an empire.***

Just to put things in context: the Medieval Warming Period was several degrees cooler than the recorded mean temperature since 1971.

The Little Ice Age

Between 1500 and 1850 CE (give or take 50 or 100 years) , things cooled off–at least in the Northern Hemisphere. Glaciers wiped out villages in the Alps. Rivers in Britain and the Netherlands froze deeply enough to support winter festivals. Even more amazing, in 1658, a Swedish army invaded Denmark by marching across the frozen Great Belt.

“Eighteen hundred and froze to death”

A violent volcano eruption in Indonesia on April 5, 1815, disrupted weather across the planet: more than twelve months of heavy rains in Europe, drought in North America and unseasonable cold everywhere.

I don’t know about you, but I suddenly feel a lot warmer.

* Brief in this case meaning 10,000 years or so.
**Short-hand for a more complicated discussion.
***Proving once again that plus or minus depends on where you stand.

Video of the Chicago Blizzard of 1967 courtesy of the Chicago Fire Department

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