Terminations of Ice Ages
It is observed that over the past several hundred thousand years, Ice Ages sometimes come to an abrupt end, with the gigantic ice sheets terminating in a mere ~5500 years. While there is ample evidence that the variation of solar input to high northern latitudes acts as a pacemaker for long-term variations in the ice volume of far northern ice sheets, there is nothing in the so-called Milankovitch theory that predicts when a termination will occur, and how it occurs. The ups and downs of solar input due to the precession cycle produce ups and downs in the ice volume but occasionally, a solar up-lobe produces a termination. But many up-lobes do not produce terminations. Evidently, an additional X-factor is necessary at that juncture to produce a termination on an up-lobe in the solar precession curve. Over the past 800,000 years, the natural state of the Earth was that of what we call an “Ice Age”. Apparently, Ice Ages occurred because the energy balance of the Earth in pre-industrial times favored production of ice sheets in the North. So, what we had was not, as one might tend to perhaps assume, unusual Ice Ages that interfered with natural periods of relative warmth. Instead, we had persistent Ice Ages that were intermittently terminated when the X-factor(s) arose, as an exception to the rule, rather than as a state of normalcy. Therefore, the search for the holy grail of Ice Ages is essentially the search for the X-factor(s) that causes terminations, along with rising solar input to the NH. All terminations occur on an up-lobe of the solar input to the NH. But many up-lobes do not produce terminations. Some up-lobes that do not produce terminations are stronger than some that do produce terminations. Therefore, an up-lobe in solar input to the NH appears to be a necessary adjunct to termination, but is not sufficient to cause termination of an Ice Age in itself. An X-factor(s) is needed to add to, or enhance the solar input to drive it over some threshold to originate runaway erosion of the ice sheets. Ellis and Palmer (2016) proposed that as an Ice Age reaches its greatest maturity, large amounts of dust from arid, CO2-deprived areas are transported by winds to the ice sheets, which in combination with rising solar input to high northern latitudes, produces much greater absorption of solar energy, thus initiating a termination. In support of this thesis, they presented convincing evidence. The X-factor appears to be dust deposited on the ice sheets. This chapter goes into the greatest detail to present evidence to support the proposal of Ellis and Palmer.