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A shorter history of the Greenland ice sheet

24 November 2013

We know it was smaller in the Medieval Warm Period otherwise Scandinavian farmers would not have colonised the edges of the ice sheet and therefore it is capable of shrinking and growing, as it did in the Little Ice Age. Now we have a paper in the journal Geology that claims the ice sheet was much smaller between three and five thousand years ago, in the Bronze Age – see http://wattsupwiththat.com/2013/11/22/study-greenland-ice-sheet-was-smal…

Ice sheets bulldoze material forwards, heaping it up. Rocks, gravels, boulders, clams, fossils, and anything else in their path builds up into long moraines on the edge of the ice sheet. Scientists can now date the clams found in moraines. This infers the Greenland ice sheet was at a low point between 5000 and 3000 years ago – and the news release was issued by the University of Buffalo.

However, the atmosphere was at it warmest between 9000 and 5000 years ago – possibly until as late as 4000 years ago. In contrast, the oceans were at their warmest between 5000 and 3000 years ago – it is being alleged. There is of course some manoevring of facts involved as tends to be the case, avoiding mentioning this and that. The researchers suggest the ice sheet responds to ocean temperatures – not global land temperatures, as such. The wobbly bit around 4000 years ago is possibly due to the cooling event described by Moe Mandelkehr at 2300BC in an SIS journal.

Geologists have been able to who when ice sheets were at their maximum extent but until now they have been unable to date shrinkage events. We can expext a bit more information to spill out of this new technique in the future – especailly when they turn to the last Ice Age. Because glaciers are like bulldozers logic dictates that rocks and fossils found in a moraine ice must have scooped them up at a time when the glacier was older and smaller. If a moraine contains fossils from 3000 years ago theat means the glacier was growing – and was maller than it is today, prior to 3000 years ago. Hence, it doesn't provide us with a graph of advance and decline and may only tell us that the end of the LB age was associated with a cooling event (which we already knew to an uncertain extent). In other words the advance at around 1000BC 'may have' covered up advances and retractions in the period 5000 to 3000 years ago. We might then ask – did it really have anything to do with a warming ocean, or is this just modern climate science muscling in on geology. The significance of this is that between 4000 and 3000 years ago we have the Bronze Age climate optimum (not mentioned in those terms) known by some as the Minoan Warm Period.

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