Friday, July 06, 2007

Younger Dryas - Why can't it happen again?

Apparently, the most likely theory of the cause of the younger dryas involves a comet impact. The Younger Dryas is a rapid cooling event of about 13K years ago, going against the trend of moving into the current interglacial period. The reckoning is that a comet caused a catastrophic melt event which rapidly sent fresh water into the northern polar region: This caused a severe disruption of the thermo-haline current, plunging the Northern hemisphere back into ice age temperatures. Extra snow and ice cover caused an albedo effect which somewhat affected the temperature of the whole Earth somewhat, giving a thousand year pause to the interglacial warming, which even more suddenly corrected globally to a warm temperature consistent with the interglacial.

Climate scientists are almost unanimous in stating that a similarly triggered iceage could not happen due to the ice melt in greenland etc. due to global warming. The two prongs of this argument are 1) that the melting is too slow to give enough fresh water to similarly disrupt the currents, and 2) the base climatic conditions are too different - ie. there are less chance that there would be enough snow/ice cover to affect the albedo enough.

Most of the fearmongering however is that the icemelt and northern polar warming is going to be much more than had been calculated just a few short years ago, and quicker than anything since the younger dryas. That, to me, means that if Europe has a sudden cooling event (whithin the next 40 years), climate scientists could still claim that they were correct.

5 comments:

Dr. Clam said...

Presumably the American megafauna would have survived through many episodes of glaciation and deglaciation, though? How does the timing compare with the disappearance of the Australian megafauna, and of the mammoth in Eurasia? I am thinking a dramatic change in climate due to a comet impact in North America would have to have implications worldwide, not just in Clovis-land.

Marco said...

Well, if the link works for you, the mammoth's disappearance in Nth America is most certainly implicated. In other areas, a lot of megafauna would have been marginalised, if not completely wiped out. I think it shows that the Biosphere is quite resilient to any rapid climate change, even if individual species are quite vulnerable to even slight changes. I do think there is a reasonable probability of thermohaline current disruption within our lifetime resulting in rapid Northern hemisphere cooling. This would make the current crop of climatologists look stupid.

Dr. Clam said...

I reckon a lake is more likely than a comet. There were a lot of awful big North American lakes that could have been suddenly connected to the ocean by receding ice sheets (the future Hudson Bay, anyone?), and I don't trust our grasp of chronology well enough to say "This didn't coincide with the Younger Dryas so we need to postulate a comet."

Dr. Clam said...

It seems the Southern Hemisphere may have cooled ~500 years before the Northern. Interesting...

Marco said...

Lake or Comet? To me, it yet could be either or both. However, they haven't really found evidence of where the lake was. The evidence of a comet appears stronger than that of the lake. The freshwater mechanism is the same regardless, and is similar to that thought to have helped along the "little ice age" of last millenium. Water currents add a chaotic unknown to climate predictions. This is why a bet of significant dropping temperatures within our lifetime would not pay extreme high odds.