What triggers ice ages?

RealClimate – February 16, 2007

This is a moderately technical blog entry discussing an article in Climatic Change.  It is not too in depth though and the average interested reader should be able to understand it.  The premise of the article is a hypothesis that there needs to be more than just changes in the Earth’s orbit to trigger the entry into or out of an ice age.

Martinson & Pitman III’s hypothesis states that the fresh water input works in concert with the Milankovitch cycle and the albedo feedback. They conclude that ‘major’ terminations can only follow from glacial build-up of sufficient magnitude to isolate the Arctic, inhibiting the inflow of fresh water to the point that salinity buildup in the surface layer from slow but continuous growth of sea-ice, causes overturn of the Arctic (through the effect on the atmospheric circulation and the ocean currents). The vertical overturning brings warmer water up from below, setting conditions that are more favorable for ice melting.


Uncertainty over weakening circulation

Letter to Physics Today – March 2007

This is a must read letter to the editor. It really calls into question one of the major beliefs of those who state that global warming will cause cataclysmic damage to our way of life. Basically, many people believe that if the major ocean currents change dramatically, that we will have major changes to our local weather in parts of the world. While this belief has some legitimacy, there does not seem to be a preponderance of evidence that such a change is imminent.