Saturday, October 13, 2018

Fire or Flood

Last summer my wife and I were hiking in the Italian Alps near the French border where we met two scientists, an Irish biologist named Chris Allen and an American geologist Allen West, who were there for two very different reasons.

Chris Allen was looking for traces of dung left by Hannibal’s elephants, to prove that the Carthaginian conqueror had come this way in 202 BC on his way to Rome. Allen West was looking for traces of “cosmogenic dust” in an effort to prove that the Earth was thrown back into an ice age by a comet.

I thought their quests were esoteric to say the least (actually Allen West sounded a few cards shy of a full deck), but both were very serious. Sure enough, Chris Allen was the subject of an extensive article in the September 2017 issue of Smithsonian about Hannibal and Allen West was one of the an authors of a major paper about the comet hypothesis in the Journal of Geology.

I don’t know much about Hadrian’s elephants, but I am familiar with the sudden change in climate that occurred when the Earth was coming out of the last ice age 12,800 years ago. Temperatures were almost as warm as today, but in the space of less than 30 years, the Northern Hemisphere cooled by about 10 degrees F, enough to push it back to ice age conditions for about 1,200 years. Glaciologists call this interval the “Younger Dryas”.

But did a comet cause this event?

After overwhelming evidence indicated that an asteroid impact contributed to the extinction of the dinosaurs 66 million years ago, scientists have wondered whether other major geologic events also had extraterrestrial causes. So far, the answer has been no, but it doesn’t stop some people from continuing the search.

An impact cause for the Younger Dryas has actually been kicking around for decades and was the subject of a PBS Nova episode back in 2009. Some researchers, like West, are convinced it happened. Most others aren’t.

We do know that when the continental ice sheets that covered North America 15,000 years ago started to melt, vast fresh water lakes formed, held in place by ice dams. In fact, such a lake once covered Westborough.

The “conventional” explanation is that as when the ice dams in northern and eastern Canada finally gave way, fresh water rapidly flowed into the Arctic and North Atlantic Oceans, eventually shutting down the Gulf Stream and the source of energy which kept the northern Atlantic warm. This idea was recently bolstered by evidence published last July, based on cores collected from the Arctic Ocean north of Canada.

The comet proponents think that the Earth was repeatedly bombarded with fragments of a large disintegrating comet over a short time period. These fragments exploded in the air, like the meteor over Russia in 2013, setting off massive wild fires throughout the northern hemisphere, creating enough dust and soot to cool the atmosphere, triggering the return to cold conditions.

The late Carl Sagan made popular the phrase “Extraordinary claims require extraordinary evidence.” Although West’s paper contain a substantial amount of data, the interpretation of that data still remains suspect and the thesis has major critics, according to a recent article in Science News.

Today, the Gulf Stream is again slowing down, as freshwater from the melting Greenland ice sheet flows into the Northern Atlantic. No one thinks we are about to retreat into another Ice Age given the level of CO2 in the atmosphere but the Arctic climate is clearly in a state of flux.

In fact, the summer Arctic ice pack volume is a whopping 75% lower than it was just 40 years ago. Current predictions are for the Arctic to be ice free in the summer by 2040.

The big lesson from the Younger Dryas is that the Earth’s climate is capable of tipping into a new state, warmer or colder, in a couple of decades if something throws it out of balance.

Given what is happening in the Arctic right now, things are clearly out of balance. Food for thought as record-setting heat waves and wildfires throughout the world are again in the news this summer.

No comments:

Post a Comment