Breaking Up an Ice Age Is Hard to Do

Blue iceberg

Atmospheric scientists and geologists seem very confident – sometimes

David F. Coppedge

Atmospheric scientists and geologists seem very confident sometimes about things they know about only indirectly, like ice ages.  At other times, though, the rhetoric turns diffident (opposite of confident).  Take this opening paragraph from PhysOrg:

Scientists still puzzle over how Earth emerged from its last ice age, an event that ushered in a warmer climate and the birth of human civilization.  In the geological blink of an eye, ice sheets in the northern hemisphere began to collapse and warming spread quickly to the south.  Most scientists say that the trigger, at least initially, was an orbital shift that caused more sunlight to fall across Earth’s northern half.  But how did the south catch up so fast?

A new theory for how the south caught up is “blowing in the wind,” the article said.  A team put together a model that invokes carbon dioxide release, wind, and Milankovitch cycles to explain how it all happened.

But all is not so tidy.  Here was global warming on a colossal scale, without man being at fault.  “We’re trying to answer the puzzle: why does the Earth, when it appears so firmly in the grip of an ice age, start to warm?”  It’s counterintuitive.  You need heat to start an ice age, and cold to stop it.  According to the new model, a chain of events led to ice age 20,000 years ago, and by 4,000 years later, the system rebounded.  Glaciers made a “spectacular retreat” while carbon dioxide from the deep ocean provided enough warming to prevent another ice age.

The article left off on a confident note that the new theory improves on old models that stalled: “Now, with the evidence for shifting southern hemisphere westerlies, the rapid warming is readily explained.”  Of course, this new model needs some more work: a Penn State scientist said, “Testing this hypothesis will be very interesting, to see whether it successfully ‘predicts’ the observed timing of CO2 and temperature changes in the south.”  One might also wonder why this irreversible chain of events occurred in the “geological blink of an eye” and not repeatedly over billions of years, if it was indeed triggered by a regular orbital cycle.  Climate skeptics might also use this theory to point out that not all global warming is man’s fault – especially one called “the great global warming of all time.”…


image credit: Eric Welch