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Originally Posted by fishjoel
Dont' confuse glaciation with ice age, they are two seperate things. Let me ask you think question...
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I was not confusing them, only noting that when people talk about the end of the ice age they are typically referring to glacial maximum. As in, whatever process was causing the ice to advance had either stopped or reversed. Its just a bit of splitting hairs.
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What are the catalysts for ice ages? Was it something that just happened as a normal cycle or is it something caused by disaster? I know our most recent ice age is believed to have been cause by an asteroid hitting the earth.
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The most common and accepted (but still debated) theory for ice ages has to do with Milankovitch cycles. I.e., the eccentricities in the earths orbit. A certain level of cooling takes place that causes increased snow in the northern hemisphere which, through the albedo effect, acts as a positive feedback for accelerated increased snow and ice advance.
Other processes that catalyse an ice age are atmospheric GHG composition, tectonic plate movements, the earths orbit around the galaxy, variations in solar irradiance...
The most important point to consider in all these effects is that the initial catalyst is always followed up by a positive feedback which has always been eventually mitigated and ended by a negative feedback. In other words, the forcings from the milankovitch cycles, variation in solar ouput, etc are not strong enough by themselves to cover the earth in ice (or on the flipside, end it).
The recent abrupt ice age you refer to is the Younger Dryas period (only lasting about 1300 years), one theory is that this was caused by a comet or comets exploding over the northern hemisphere (like Tunguska but orders of magnitude larger). This theory has enjoyed some pretty strong evidence lately with the discovery of nanodiamonds in a layer of the earth in multiple clovis locations.
The other more popular theory is that a massive influx of fresh water from the deglaciation of the wisconsin ice age shut down the thermohaline circulation in the north atlantic. This locked the global climate into a cooling phase until the north atlantic froze completely, and moved the fresh water to the surface, allowing the thermohaline circulation to resume.
Andrew