While the Field Archaeology Branch was working with the Dorset Roman Group on the Roman Road to Exeter it was found that both Societies had people interested in the Ice Ages, and between them came up with an explanation.

Ice and other cores show that the Ices Ages had periods of 40k years 2m years ago, becoming a 100k year period 1m years ago. Explanations have involved small changes in sunlight from the Earth's orbit every 41k years, and even smaller ones at 90k and 120k years. It is not seen how these produce such large polar changes. A recent paper reported a computer simulation of the Earth's sunlight over the last 400k years with no measurable period observable around the present 100k-year period (Ref 1).

It is understandable that snowfall causes the Polar Caps to spread outwards, which will thus reflect more sunlight and so lower global temperatures - encouraging further spreading of the Caps. Eventually one expects the Polar Caps' edges to reach warmer latitudes, where the rate of advance equals melting. The Caps should stay at this Equilibrium, but subject to fluctuations in the climate.

But having spread out for 90k years with slowly falling global temperatures, the Caps then rapidly retreat for 10k years with rising global temperatures. There has been dozens of these Ice Age Cycles running like clockwork.

Our explanation for this rapid retreat rests on the facts that: (i) the Earth's core is at 5k degrees, (ii) this give a heat flow of ~ 0.1 watt per sq m at the Earth's surface, (iii) ice thickness of ~ 3km in the Polar region acts like a blanket causing the rock surface to be above 0 degrees C - so melting the bottom of the ice, (iv) ice thickness in the S Polar region is 4 - 8kms and under ice lakes are known.

Peter Laurie calculated that for an Ice Cap stretching to 50 degree of latitude this geothermal heat flow would melt the volume of water released in the last retreat of the Caps in 78k years (Ref 2).

However the Caps only cover all this area for a part of the time. An estimate of how much ice can be melted by geothermal energy is given in Ref 3. Conditions today are near Ice Age minimum. At Ice Age maximum the Height of the ice is much higher, thus the Rate of Outflow is much higher, which in turn controls the Advance of the Caps. It is necessary to chart the form of these key variables over the Ice Age Cycle in order to see how much of the Poles were covered by a blanketing thickness of ice (causing melting at the rock surface) at intervals over the Ice Age Cycle. About 60% of the water released during the last retreat of the Caps was likely to be already melted under the Caps from Geothermal energy since the previous Ice Age minimum.

The picture is therefore as the Polar Caps build up in height and flow outwards, ice at the rock/ice surface melts. By Ice Age maximum c 2/3km deep lakes will exist at the S Pole. However the only place that this melt can leak out is at the edges of the Caps - which will become stationary as Equilibrium is approached - allowing the melt front to catch up. A climate fluctuation may then cause the Polar Caps to retreat slightly - exposing the melt front - and the under ice lakes then leak out rapidly. Ref 1 shows that one of their simulated sunlight peaks generally does this (though others simply give a small temporary retreat of the Caps). This is why statistical connections have been found, but they are not the principal cause.

This flow of water under the ice will then increase the ice movement away from the Poles, which will cause the ice to thin and fracture - as well as pushing the Cap's edges beyond Equilibrium so increasing melting. Ice will be washed away by the escaping melt in rivers, or ice burgs breaking off the Cap's edges, both to melt at lower latitudes. As less of the Caps are covered by ice more sunlight is absorbed, raising global temperatures.

Ref 1 gives an explanation for the Ice Ages based largely on the idea that the weight of Ice causes the ground surface to sink - but there are delays of thousands of years. They propose that these delays happen to cause the ground surface to sink at the point of the maximum extend of the ice - thereby lowering the ice surface to an altitude where it melts. I show in Ref 4, with respect to the Height of ice and Outflow of Ice at relevant times, that lowering of the ground surface will be made up by snow at the poles. So the ice surface will not be lowered - so another explanation for the rapid Caps retreat is needed from that proposed in Ref 1. Even so, under ice lakes would still form and melt 60% of the water released which will aid the rapid retreat.

There is a connection with climate change in which members of the two Societies involved tended to be sceptical. There have been dozens of Ice Ages running like clockwork. Fig 4 enables a more informed debate of how long we have to melt the polar caps - likely to be needed to prevent the next advance, with the UK under miles of ice down to London, and all of Canada and parts of the USA. For once the ice sheets start to roll outwards again we may be powerless to stop them. The winter extent of the S Polar Cap has been growing since records began in 1979. On 15 September 2014 it broke this record (Ref 5). Are we already too late?


Assistance from P C S Laurie, (Dorset Roman Occupation Group; A L Systems, who produced the calculation of ice melting time. Richard Whaley


1. A. Abe-Ouchi et al, Nature 8 August 2013, 500, No.7461, p190
2. Peter Laurie in the on-line version of this paper
3. Richard Whaley in the on-line version of this paper and Figs 1 - 5.
4. Richard Whaley, Comment on the on-line version of Ref 1. (Nature sub needed, but available in any Hants Library - go to Access Research, enter Nature (London) into the search box. Use a result leading to the archieve, find the issue containing Ref 1.)
5 Antarctica extent of Winter Sea Ice, New Scientist 20 September 2014, p6
6. Peter Laurie, Ice Age cores

Debate & Discussion

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Figs 1 - 4 of online version of paper

Overall caption for Figs 1 – 4: The phases of the various parameters involved in the Ice Age Cycle are presented for discussion. Ice Age Maximum is at Year 0, Ice Age Minimum is at Year 10K, and the next Ice Age Maximum is at Year100K.

Fig 1 The Ice Age Temperature Change is the prime fact coming from ice and other cores. The change is 10 to 12 degrees C. The Temperature rise is fast over 10K years, and slowly falls over 90K years. There is a lot of noise or random Temperature fluctuations, but the basic form of saw tooth wave is given in the Temperature Change graph (Ref 6).

Fig 2 Ice Height. The leak out of under ice melt from Year 0 speeds up the outflow of ice considerably which must result in reduction of polar ice thickness and height, until Year 10K, when the ice will be near minimum height. With Temperature at its maximum but slowly falling it will be well above its average for 10 – 20K years. Further slow thawing and reduction in extent and height of polar ice may occur. Eventually the excessive heat in Earth’s crust in polar regions caused by the former blanketing will radiate away, lowering Temperature, and causing polar caps to start rising in height from increased snow. This will continue until maximum height is reached around Year 100K.

Fig 3 Outflow of Ice - Speed. Out flow of polar ice will rise considerably by leak out from Year 0, and increase as more leak out sites occur – until leak out ends around Year 10K, when speed of outflow will become near minimum. Thereafter outflow will be a function of the Height of Ice, especially around the S Pole - until the next leak out starts around Year 100K.

Fig 4 Advance / Retreat of Ice. From Year 0 leak out will cause Retreat of the Polar Ice, aided by more of the sun’s light being absorbed by the smaller Polar Caps increasing Temperature, until leak out ends around Year 10K. Thereafter the Advance of the Caps will be a function of the Speed of Outflow of Ice, which will eventually push the edges of the Caps outwards, then aided by more sunlight being reflected and lowering Temperature. Advance of the Caps will start to level off as Equilibrium is approached around year 100K.