| Date |
Description |
Ref: |
| |
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 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 |
| ~9500 BC |
|
|
| ~11000 - 9600 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 ~11000 BC, reaching a depth of cold ~ 10500 BC (note the short
period), 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 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,
perhaps higher than today. |
1, 17 |
| 8000
BC |
|
|
| ~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.
[ 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. |
| 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 |
| 5500 BC |
|
|
| 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. |
1 |