Wednesday, August 7, 2013

Hot (not): a cold blast from the past

I concluded Hot: Climate change happening at record pace with the following program note.
I have one more climate change story from last Saturday's OND, one about how a rapid climate change in the other direction may have contributed to extinctions.  Stay tuned.
The story comes from the BBC.

Ice core data supports ancient space impact idea
By Simon Redfern Reporter, BBC News
August 1, 2013
New data from Greenland ice cores suggest North America may have suffered a large cosmic impact about 12,900 years ago.

A layer of platinum is seen in ice of the same age as a known abrupt climate transition, US scientists report.

The climate flip has previously been linked to the demise of the North American "Clovis" people.

The data seem to back the idea that an impact tipped the climate into a colder phase, a point of current debate.
The tip back to a colder climate is not the issue.  In fact, it's a key point of "An Inconvenient Truth," which I'm showing to my Environmental Science class this week.  Here's the relevant question from the worksheet.
What is the likely effect of the melting of the Greenland ice cap on ocean circulation and global climate?
In the movie, the idea is that the release of meltwater from a large glacial lake diluted the Gulf Stream, causing the water to become less dense and unable to sink to the bottom of the ocean off Greenland, jamming up the global thermohaline circulation and sending the planet back into an ice age for another thousand years.  An analogous melt of water from the Greenland icecap, which is beginning to happen, would do much the same thing, slowing ocean circulation and cooling Europe.  Both of those are indeed taking place.

The effect of the proposed meteor impact would be that the explosion itself caused the flood and then added the cooling effects of all the dust from the impact on top of it.  That doesn't mean that the slowing of the Gulf Stream and cooling of the area around the North Atlantic isn't going to happen; it already is.  Instead, it means that the magnitude of the cooling that results won't be as big as happened 12,900 years ago.  That might actually be a good thing.

Another thing the impact would do would be to lessen the culpability of humans in the extinction of large mammals in North America and Europe at the time.  Humans definitely contributed, but a meteor impact would definitely shift some of the responsibility off of our ancestors.  It would also make the case for the deadliness of asteroid impacts, as if that wasn't already in the news.

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