The 8.2 ka event

A most interesting blog post from RockyRex, about an anomalous episode during the warm up from the last ice age, when, for a period lasting just 150 years, global temperatures plummeted before resuming their up trend.  Scientists now think that this was due to the catastrophic failure of an ice dam which had been keeping a very large body of meltwater behind it.  When this fresh water flooded into the sea, it affected the thermohaline circulation of sea water.  Fresh water is less dense than salt water, so it remained on the surface of the sea, displacing the gulf stream further south and weakening it.  Northern hemisphere temperatures dropped 2 C in a couple of decades, and the sea level rose by between 0.4 and 2.1 metres.

The current rapid melting of Greenland's ice cap appears to be producing a similar "cold blob" in the Atlantic, and the Gulf Stream has slowed.  If this process gains strength--very likely as Greenland's melt accelerates--there will be a temporary (100 years plus?) cooling of the North Atlantic.  No doubt the denialists will say, see, we told you so, the world is cooling.  What seems to be certain though, is that this "cold blob" combined with much warmer seas around it, is responsible for the record floods in Scotland and Northern England over the last few years.

Read more of RockyRex's post here.