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Ice Ages

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36323.  Thu Dec 01, 2005 5:29 am Reply with quote

Andy O'Neil posted on the outer boards an assertion that the reason why the Thames doesn't freeze over any more is that it has been made artificially narrower by the construction of the Embankment etc, so the water flows faster. I had always understood the issue to be at least partly to do with a mini-Ice Age, and I haven't looked into the subject yet. However, the subject might lead us to this:

Q: When did the most recent ice age end?
F: Any number
A: We're still in it.

Glaciologically, an ice age is a period in the Earth's history when there are polar ice caps. Our current temperate climate is an interglacial period, which started 10,000 years ago, in the (perhaps) fourth Ice Age. When this will end is anyone's guess; ideas about the duration of the interglacial period range from 12,000 to 50,000 years (without allowing for man-made influences).

The causes of the fluctuations are not well understood. Possible factors include: the position that the land masses happen to be in, the composition of the atmosphere, changes in the Earth's orbit around the Sun (Milankovic Cycles) and possibly even the Sun's own orbit around the galaxy.

The mini-ice age which peaked in the 17th century coincided with the 'Maunder Minimum' - a period of extremely low sunspot activity, though whether the two were causally linked is a matter of debate. During this period the Arctic ice sheet extended so far south that eskimos are recorded as reaching Scotland in kayaks on six different occasions:

s: Wiki articles on 'Ice Age', 'Little Ice Age' and 'Maunder Minimum'.

57998.  Wed Mar 08, 2006 7:00 am Reply with quote

For the Ice Age notes:

A recent study has hypothesised that the latest mini ice age (as mentioned above) may have been caused by the Black Death (possible link to Ring-a-ring-a-roses here?).

The idea is that there was an agriculture crisis around 1347 which lead to a rise in CO2 which in turn lead to the dip in temperatures:

The team found an increase in cereal pollen from 1200 onwards (reflecting agricultural expansion), followed by a sudden dive around 1347, linked to the agricultural crisis caused by the arrival of the Black Death, most probably a bacterial disease spread by rat fleas.

Counting stomata (pores) on ancient oak leaves provided van Hoof's team with a measure of the fluctuations in atmospheric carbon dioxide for the same period.

This is because leaves absorb carbon dioxide through their stomata, and their density varies as carbon dioxide goes up and down.

"Between AD 1200 to 1300, we see a decrease in stomata and a sharp rise in atmospheric carbon dioxide, due to deforestation we think," says Dr van Hoof, whose findings are published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

But after AD 1350, the team found the pattern reversed, suggesting that atmospheric carbon dioxide fell, perhaps due to reforestation following the plague.

The researchers think that this drop in carbon dioxide levels could help to explain a cooling in the climate over the following centuries.

Unfortunately there's a lot of "We think"s and "may"s in the article, but it's an interesting enough theory.


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