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<<<<11000 - 4000 BC
 Date  Description  Ref:
   4000BC - 100BC  
 ~4000 - ~3500 BC "Climatic optimum": peaked circa 4000 - 3500 BC (some references say 4000 - 2500 BC); markedly reduced glacier extent (all gone from British land mass). (var. refs); tree-lines in northern areas, particularly northern England & Scotland roughly 300m (or 1000ft) higher than they are now, with forests established at higher elevations than currently: this implies that wind-damage might not have been a major problem. This in turn translates into weaker, less frequent spells of significantly low pressure (i.e. major cyclogenesis spells). (see also previous date file .. this period started circa 6200 BC).
As to sea levels, Lamb tentatively suggests that they rose by ~100-150ft / ~30-45 cm between 8000 BC & 3000 BC.
Both globally & regionally, several references mention an anomaly of ~ + 2degC over those values relating to the latter third of the 20th century.
~3500 - ~3000 BC  Tentative suggestion of a 'downturn': climatic conditions decade-to-decade now more variable, with occasional cooler / colder & wetter periods, BUT overall this spell still warmer than today! Storm tracks are thought to have been directed more towards the British Isles (perhaps biased to southern areas), and more vigorous. Periods of heavy rain, severe gales - these more frequent, and summer warmth was less reliable - with runs of such seasons classed as " wet and cool". European glaciers advance (again, but not in Britain) and forests retreat from higher elevations (storm damage?). Decline in warmth-loving tree species. ( a 'disturbance of the global regime': [Lamb] )  1
 3000 BC    
 ~3000 BC onwards Bronze Age recovery (after previous, relatively short-lived downturn): freedom from major storms, excessive rainfall etc., and renewed increase in temperature. Glaciers & 'permanent' snow-patches less prominent. Increase in forest cover back to more 'exposed' (in modern terms) western / upland areas. Renewed building of stone circles - possibly as observatories - this suggests lower cloud cover amounts than before. The Elm & Lime tree 'northern-most' line moved north, and woods probably grew on Orkney & exposed NW Scotland, therefore again implying milder and, perhaps more importantly, much less windy conditions than the modern era.  1,
 ~2200BC  'Major VOLCANIC eruption'. (possibly in/around Iceland, disrupting the North Atlantic and/or Arctic circulations).
Bitterly COLD winters & indifferent, occasionally poor summers.
 ~1500 - ~1300 BC A possible 'sharply' cooler period (the 'Neoglacial'), when glaciers advanced in Alaska and the Alps. Growth in peat bogs - large fluctuations (inundation) of marginal land around Alpine lakes (implies additional precipitation). [However note that overall temperatures still warmer than current - these are small-scale fluctuations - in fact we are here in a broadscale downturn in temperature from the warmth of the Bronze Age to the chillier late Iron Age.]  1
 1159BC  'Major VOLCANIC eruption'. HEKLA (Iceland): COLDER/WETTER conditions for Europe (at least). Crop failures/famine. [ Be wary over exact dating of such as volcanic eruptions in these ancient times; no-one was actually recording the event in a contemporary sense, so dating comes down to interpreting ice cores, ancient tree ring records etc., and a decade either way of error would be quite likely.]  20
 ~1100 - ~900 BC Periods of extended warmth (in a longer-term post Bronze Age cooling phase). Frequent dry, 'blocked' spells of anticyclonic weather - however this begs the question - were the winters often bitterly cold?  1,
 ~900 BC - ~650 BC  Broadly, after 3000 BC, there are signs of increased frequency of cooler/stormier episodes, and in particular, between ~900 BC & ~650 BC [ some references have 1000 - 500 BC as a short-hand ], there was a marked increase in storm frequency.
In the west & north of these islands: increased 'wetness', cooler, more unsettled & stormier. Evidence of much trackway building. Rapid growth of peat bogs. Woodland decay with treeline moving both south (in latitude) and lower (in altitude) & retreating from exposed / west-facing coastal areas. It may be also that the tendency to build 'hill forts' was a response to wetter conditions overall - but this is subject to debate.
In the east & south: no detectable changes within this period - indeed, most researchers state that it was notably drier in the east: however, the increased storminess implies some effects such as coastal inundation. To get this 'north & west/south & east' split, the mean flow must have been a highly westerly type. [ See comments on broadscale flow in section below.]
 850BC  "Fimbul winter": Harsh conditions affecting high-latitude areas (revealed in Nordic sagas) - possibly connected with downturn in solar / sunspot activity, and/or increased cosmic rays. The subsequent reduction in direct radiation from the sun led to COOLER/WETTER conditions. ("The Long Summer"/Fagan)  20
 ~650 - ~200 BC A general increase in rainfall (& presumably snowfall - temperatures falling). Western & highland areas notably wet - abandonment of upland settlements, and retreat of tree-line to lower altitudes. The east now also become wetter (see above), suggesting a tendency to cyclonic activity over the British Isles (rather than passing to the NW). By ~200 BC (but some researchers suggest this date should be much earlier - say ~300BC or before), it is estimated that mean European temperatures were at least 1degC below those of the warmest post-glacial period (possibly as much as 2degC, which latter would be a highly significant number). Over the whole period of this last millenium BC, there was major glacier re-growth in Europe, and falling sea-levels (i.e. the reverse of the conditions we are seeing today).
~300 BC [ but disputed by some research - could be more like ~400/450 BC ]: possible peak of stormy, wet conditions in NW Europe (including the British Isles). Rainfall possibly as much as 40% higher than late 20th century values. Summers frequently cool / unsettled. Significant evidence of wooden trackway construction across British lowlands to avoid long detours round flooded land (and also to enhance security - 'hill forts' may also come into play here).
In the broadscale, the period ~900 BC to ~200 BC is one where it is thought that the Polar vortex was expanding / cooling, therefore both increasing the jet strength (greater vigour of depressions) and nudging the whole pattern southwards.
 ~200 BC - 350 AD
" Roman expansion & domination "
~200 BC: Beginning of a notable upturn in temperature levels. A steady recovery (after the cooler late Iron Age) from now, right through the 'Roman-British' period, only petering out somewhere around 350 AD. Mean temperature levels based on 'middle' England would peak at around, or a shade below those of the 'Climatic Optimum' of the Early Middle Ages & precipitation amounts overall were declining - though adequate. The climate would become generally 'benign' by the time of early years of the 1st Century AD, and eventually villas became bigger and built on hillier sites in areas we would not normally construct 'high status' buildings (at least until very recent times). Southern Britain in particular self-sufficient in wine (a staple of Romano-British life, not a luxury), and there is evidence of export of same, implying very good conditions for growth / ripening.
However, there are records (principally from the Roman occupation period), of 'severe / snowy' winters. This is a warning to us nowadays not to assume that a 'warmer' climate necessarily means we will not have 'severe' winters. Sea levels thought to have risen between 1 and 2 metres compared with before and after.
120 - 114 BC (but see body of this note re: dating): Either a 'great' storm, or a series of storms in the North Sea basin. Sea floods, which affected the coastlines of Denmark, the Netherlands & Germany - if so, these storms must also have affected the east coast of Britain. These events are supposedly consistent with the change in temperature regime, as it implies alteration and/or intensification of jet-stream patterns etc., which often accompany major changes of climatic type - but read on . . . . . In many texts, the so-called "Cymbrian (or Kymbrian) flood" of the coasts around the German Bight is reputed to be responsible for setting off a migration of Celtic tribes. [23] (This is quoted by Lamb with the date range given at the head of this paragraph; but there's something odd here: the source is the Greek writer Strabo (living in what was at the time part of the Roman Empire), who lived ~63/64BC to 24AD, who in turn was quoting earlier writers (also Greek). In particular, Strabo comments upon the writings of Clitarchus (or Cleitarchus), who tells the tale of horsemen not being able to outrun an incoming (?flood?) tide and who is credited with living in the 'last quarter of the third century BC', or before 300BC. This means that this so-called 'flood' must have been some two or more centuries before the date given here! The idea of a single flood event setting off a wholesale migration is also difficult to comprehend - more likely a series of damaging floods / storm events, in the area that we now know as the Dutch polder-lands. This timing [ i.e. latter part of the fourth century BC ] would also tie in well with the suspected downturn in climate fortunes, with increased storminess across NW Europe and general cooling [ see 650BC - 200BC comments above.)
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