Saturday, December 17, 2016

The Day After Tomorrow

“It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.” – Samuel Clemens

Anyone remember the 2004 movie “The Day After Tomorrow” where global warming throws the world into a new ice age overnight and we all end up as refugees in Mexico? I won’t blame you if you don’t, because it was a pretty forgettable movie whose premise was based on a novel written by a guy who is still certain he was abducted by aliens in 1983. 

Catastrophes do happen though and the realization that they have happened on a worldwide scale represents a paradigm shift in the fields of geology and paleontology. I can pinpoint the exact day that this shift occurred – June 6th, 1980, when Luis and Walter Alvarez published “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction” (layman’s translation: - “The Day the Killer Asteroid Wiped out the Dinosaurs”) in the highly regarded journal “Science.”

It took well over a decade, but the scientific community finally decided the Alvarez’s were right. Subsequently, when geologists went back to look at the geologic record with a new perspective, they came the realization that many other geologic events like mass extinctions probably occurred far more swiftly than originally thought.

Like all geologists, I learned that the “present is the key to the past” - that the slow and steady geologic processes we see today can explain the geologic record. This principle was espoused by Charles Lyell, considered the “father of geology.” Back in the early nineteenth century Lyell’s principle was very insightful, based on his scientific observations at the time, but we know a lot more now than we did almost 200 years ago.

Today, earth scientists of all stripes look at the geologic record with the perspective that “the past could be the key to the present,” which finally brings me to the main focus of this week’s column.

Our current climate is part of an “interglacial” – a warm period between ice ages.  The last interglacial occurred 125,000 years ago, a time period called the Eemian when the CO2 concentration was 285 ppm, roughly where it was just 200 years ago, when Lyell was a young man. Atmospheric CO2 is now above 400 ppm and increasing at rate unlike anything seen since the demise of the dinosaurs.

The interesting thing about the Eemian is that although global average temperatures were just a tad bit warmer than today, sea levels were 6 to 9 meters (20 to 30 feet) higher. 

So what does the Eemian have to say about what’s going on in our world today? Recent peer-reviewed papers published in the last few months have investigated this question. 

One paper looked at what rapidly warming air could do to the Antarctic Ice shelves, which sit on the ocean floor and hold back the glaciers on the Antarctic continent. This paper calculates that the Antarctic glaciers could collapse within the next 100 years due to a process called structural failure.

Just as dams can fail when their structure is too weak to hold back the water, the cliffs of ice at the edges of the ice shelves can also fail when they become too weak in the warming polar atmosphere, causing the rest of the ice shelf to collapse like lines of dominos.

Another group of scientists, led by James Hansen, formerly of NASA, calculate that cold, freshwater from the melting Greenland and Antarctic ice caps will cool the ocean’s surface waters, trapping warmer water at depth where they will start to melt the ice shelves from below, accelerating their disintegration, leading to ice shelf to collapse and rapid sea level rise within the next 100 years.

I would note that over the last few years, signs of this surface ocean cooling and deep water warming are already being measured in the far northern Atlantic south of Greenland and in the Southern Ocean off of Antarctica.

So, here we have two recently-published peer-reviewed papers, both of which describe how the Antarctic ice cap could collapse a whole lot faster than anyone thinks, leading to significant sea level increases in a matter of decades that until recently was thought would take centuries. 

Both papers suggest that the planet could be near a tipping point, when our global climate could change quickly. Not Hollywood-disaster-movie quick, but within-our-lifetimes quick.
Are these predictions accurate? 

Hansen’s predictions and calls to action have been described as alarmist. On the other hand, maybe we should be alarmed.


Hansen testified before Congress in 1988 that global warming had begun and used his mathematical models to predict that global average temperatures were set to increase by about 0.75 degrees C by 2005. 

His now 30-year old predictions were pretty much spot on. 

That’s why.

Originally published in the Westborough News on 04/08/2016

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