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|11000BC - 4000BC|
|12000 BC onwards||Period of ending of the last great Ice Age. Rapid warming in the period up to ~ 11500 BC, steadier warming thereafter: by 9000 BC, major ice sheets had been eroded significantly, though were (possibly) still in evidence in the Highlands of modern-day northern Britain. As regards conditions over southern Britain, by ~11500 BC, it is estimated that mean winter-time temperatures were between 0 and 4degC ( perhaps a little lower than today's values) & high-summer values between 12 and 16degC, again a little lower or similar to current figures.||1, 4, 17|
|~11000 / 10900 - ~9600 / 9500 BC||The 'Younger Dryas' reversal (YDR) [ also known as the 'Loch Lomond' stadial ]: a 'reversal', because it has been found to be a sharply colder period in what was a general rise in temperature after the end of the last Ice Age. The downturn is thought to have started abruptly ~10900 BC, reaching a depth of cold ~ 10500 BC, when average temperatures are thought to have been: mid-winter, -16 to -20degC [ at least 15C below modern values - a truly dramatic fall ] and high-summer, 8 to 12degC, about 4C below modern values. This would have been disastrous - given the ~50yr period over which the decline is thought to have occurred: if it were to happen today, it has been argued that civilisation as we know it would cease. From ~10000 BC, a slow, then rapid recovery, and by ~9500 BC, temperature levels back to pre-YDR values.||1, 17|
|8400 BC||By about this time, the post-Glacial rise in temperature (& increase in humidity) had resumed: estimated temperatures were: mid-winter 0 to 4degC (similar to today) & high-summer 14 to 18degC.||1, 17|
|~8000 - 6500 BC|| Sea level had been
rising, in response to post-Ice Age warming, since ~ 8500 BC. The rise
continued up to ~ 2500 BC, but the major sea-level uplifts occurred within the
period 8000 & 6500 BC: by the latter date, most of the 'land-bridges' (e.g.
Dover Strait, North Channel) had gone, with a rapid retreat of the major
glaciers. At 8000 BC southern & eastern 'North Sea' was essentially land
(or a marshy region), whereas by 6000 BC at the latest (varying ideas on this -
some have 7500 BC), it was mostly sea. It is thought that the last Ice Age
glaciers disappeared around 8000 BC from upland northern Britain.
[ Sea levels rise due to a combination of melting of land-based ice (e.g. the glaciers), and thermal expansion of the sea-water.]
|var incl 6.|
|6200 BC onwards||The Atlantic climatic
era: the period 6200 BC - 3500 BC (approx.) is now regarded as a major
'Climatic Optimum'. In the NW Europe / NE Atlantic region, pressure is thought
to have been relatively higher, with the depression tracks much further north
(and / or south .. e.g. highly blocked) & less intense than before or
since. The northwest of these islands were warmer, drier & less 'stormier'
than modern conditions.
Mean annual temperatures eventually (by latter part of this "Atlantic" period, i.e. 3500 to 4000 BC) it is estimated that a +2 degC anomaly (c.f. 1960's) was probable, with warm winters. Moderate humidity overall, but periods of heavy rain, some of lengthy duration. Rainfall evenly distributed winter to summer. (4600 - 3500 BC: moderate dryness.)
|1, 17, var|
[+/- 2000 yr]
|A huge volcanic eruption occurred on Sumatra (in what is now Indonesia): thought to have released 2800 km^3 of ash & pyroclastic material, which is estimated to be at least three times that released by the modern eruption of Pinatubo in 1991 (q.v.) This would have had major effects on the world's weather for several years, perhaps decades, after.|| [ 'Weather',
August 2008 ]
|5000BC||Although it is probably dangerous to put a particular year to an event this far back in history, many researchers regard the period around 5000 BC as the warmest in post-glacial times: the discussion revolves around whether our current spell of warmth is comparable & I'm not yet sure there is any sort of definitive answer. Lamb (reference 6) puts the mean temperature for this era at around 2degC above the second-half of the 20th century values; remember that in the current 'Global Warming' debate, we're usually talking about differences much less than this.||1, 6|
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|4000 - 100BC>>>>|