Wiki has a good piece on the Piora Oscillation, the official name for the period of global cooling that followed on from the 3200BC event. It lasted for 200, maybe 300 years in duration and divides the Pre-Dynastic phase from Dynasty One. In Sumeria it marks the end of the Uruk phase with a confused episode dividing it from the Early Dynastic Period. There is plenty of evidence to suggest horse mounted barbarians arrived from the steppe zone at this time – including the Royal Graves of Ur which mimic the kurgans that littered southern Russia and western Siberia in the 4th millennium BC. It is therefore an important dividing zone in the most developed civilisations of the period (and changes occurred in India and China at the same time). The name comes from the Piora Valley in Switzerland. Glaciers advanced in the Alps during the oscillation – the tree line dropping by some 100m. In New England (USA) hemlock and elm trees suffered a decline. Similar evidence is known from California. In the Levant, the surface of the Dead Sea rose dramatically (as a result of a large increase in rainfall) but falling back later. Some places in the Persian Gulf were also flooded – most famously at Ur (Leonard Woolley excavations). See for example https://en.wikipedia.org/wiki/Piora_Oscillation – or just put Piora Oscillation into your search engine and lots of other links will turn up.
The Belfast tree ring chronology set the onset of cold weather at 3150BC (suggesting cold weather in Ireland and Britain, and NW Europe in general). The Greenland ice cores have an acid spike at 3150BC (probably a volcano) but the Gisp 2 ice core shows a sulphate spike also in 3250BC, together with a methane trough. Is this a signature of a volcano or of a cosmic event (atmospheric explosion of meteoric or cometary material)?
In Germany, there was an increase in swamp oak (or bog oak in Irish terminology) suggesting water logging (as in Ireland and Britain) and possibly evidence of heavy flooding with the jet stream much further to the south than normal. Even in the American South West, if only on a temporary basis. In Morocco there was a decline in oaks (as a result of declining rainfall, right across the Sahara region). The Nile flooded – giving rise to the myth of the inundation (perpetuated thereafter by the annual flooding event fueled by winter rains on the Ethiopian Highlands).
Paul Dunbavin, in his two books, 'The Atlantis Researches' and 'Under Ancient Skies' speculated there might have been a small axis shift around 3200BC (an idea that has recently resurfaced in CR Sant's book, 'The Calendars of Megalithic Malta' where there appears to be a change in the position of solstice sight lines at this time. We may also note a distinct shift in megalithic architecture elsewhere in Europe at this time. In Britain, it marks the end of the causewayed enclosure and the long barrow and the appearance of the round henge and circles (including round houses). It is useful to note that even a small readjustment in the geoid of the earth would involve global water bodies relocating, and changing sea levels. However, the close passage of a comet would at first cause heavy evaporation followed by a lot of water falling out of the sky after it had passed by. Whiston postulated a possible close approach of Comet Halley in around 3000BC – but that was a long time ago and nothing much has come of the idea. Likewise, shifting jet streams could be all that is required for regional flooding and heavy rainfall. It would require a heavy volcanic episode (or a dense meteoric/ fireball event) in order to cause the atmosphere to become laden with soot and debris in order to maintain a cold period over a couple of hundred years. For the moment the cause of the Piora Oscillation is an unknown but mainstream has an aversion to catastrophic cosmic encounters and therefore most theories revolve around hypothetical cycles of 1500 years (or variations thereof). The cycles are of course just that – periods of time. What causes them is the interesting part. Cycles can arise simply by computer simulation (and may be just waffle in the wind). Cycles can also occur as a result of cosmic orbits.
This period is also connected to the Maya calendar beginnings, at 3114BC. Is that just a coincidence? We also have Oetzi the Ice Man buried in a creeping glacier when he was high on the Alps (above the tree line). He seems to have been entombed and preserved because of a sudden onset of cold weather. On the other side of the world, in the high Andes of Peru, there was a similar cold spike that was brought on quite suddenly, entombing plants in ice at the Quelccaya Glacier. These emerged in the late 1990s as a result of the glacier shrinking. In addition, the Age of the Kali Yuga, in Hindu tradition, began at this time – and was associated with a visit to the people of earth by one of their gods, Krishna. The visit may well have been observable in the sky.
Further information on the climatic event is available in HH Lamb's 'Climate History and the Modern World' where he shows pretty clearly it was a world wide phenomenon, claiming the Piora Oscillation affected Kenya and East Africa (drought) and the Columbian Highlands (upper frost limits), and even in Alaska (vegetation changes). He says it lasted no more than four centuries and probably somewhat less. Even in Australia there is evidence of climate shift. In Africa the changes are associated with a shift in the monsoon track – with people moving out of the Sahara. This is in the news recently as CAGW adherents are trying to blame the drying up of the Sahara on human activity. Clearly, modern climate scientists do not read the writings of older climate scientists such as HH Lamb. See for example https://phys.org/print408702531.html
In Britain people appear to have reverted to pastoralism (they may have never dropped it in fact as there is a long tradition of animal husbandry going back to managing deer herds and aurochs in the Mesolithic period). Livestock farming remains the major farming activity on the wetter western side of the country – Wales, the Lake District, the Isles and western Highlands. Human activity seems to have declined around 3200BC in Britain, but that may be ephemeral as surviving houses of the Neolithic period are few and far between. Nevertheless, Aubrey Burl, in 'Prehistoric Avebury' said, the years between 3250 and 2650BC constitute a dark age in the prehistory of southern Britain, a period of time from which little has survived. This view may of course have changed somewhat as recent archaeology has helped to fill in the picture – but we can assume a drop in the population probably did occur.
At https://notalotofpeopleknowthat.com/2014/07/20/hh-lamb-and-the-early-hol… … provides more evidence on the period in question. He has scanned some of the pages of HH Lamb's book which is now out of print apparently. I have a copy so may come back on this one. The blog author's beef is that HH Lamb is ignored by the current crop of climate scientists yet he pioneered the subject in this country – and was involved in the set up of the climate science unit at the University of East Anglia. Lamb was crystal clear about the meteorological causes of the weather. During a warm phase of climate, the norm may we say, all of the global weather systems move towards the poles (shrinking the polar zone and creating an extended temperate zone as we enjoy today). The anti cyclone system and North Atlantic storm zones are confined to northerly regions. As a result, equatorial and monsoon rain systems are also higher in latitude (although these are also affected by earth's orbit around the sun). The Piora Oscillation involved a cooler global climate and the weather systems moved southwards – including the anti cyclone and storm tracks (related to the movement south of the jet stream). It's all quite simple really – but then we don't know what causes sudden and abrupt changes (apart from volcanism).
At www.ancientpenwith.org/bronze.html … we get the effect of the Piora Oscillation on Cornwall. One result was an abandonment of upland zones such as Bodmin Moor. The site is New Age but full of links to useful information. A fuller picture of glacier growth and decay during the oscillation is in an article in Quaternary Science 28 (2009), 'Latest Pleistocene and Holocene glacier variations in the European Alps' by Susan Ivy-Ochs, H Kershner, Max Maisch, Marcus Christl and Peter Kubik. The full paper is available at …. https://www.ldeo.columbia.edu/res/pi/tcn/Lamont_Cosmogenic_Nuclide_Lab/R… (see abstract at www.sciencedirect.com/science/article/pii/S0277379109001152 ) and https://www.uibk.ac.at/geographie/personal/kerschner/ivyqi2006.pdf .. which focuses on the early Holocene.