Britain, 5000–2000 BC: no ice, no catastrophe, a familiar climate

An interactive, fully referenced viewer of published palaeoclimate proxies for Britain across the Stonehenge-building millennia is now online: 

Climate of Britain, 5000–2000 BC.

It draws on twelve independent proxy records: peat water tables, cave speleothems, lake chironomids, ice cores, ocean sediment, a pollen-based reconstruction and tree rings, each carrying its own citation, archive link and stated uncertainty. Three findings fall out of it directly.

Stonehenge - 2013 - Tim Daw

The Avon would not reliably have frozen thick enough to drag stones over

One proposed route for moving sarsens to Stonehenge has them dragged across the River Avon on a surface of thick winter ice. The pollen-based reconstruction gives a direct check on this: mean January temperature for Wessex across all four millennial slices in the window comes out at 2.7–4.2 °C — above freezing, and close to the modern Boscombe Down January average of 4.0–4.6 °C. A monthly mean sitting a few degrees above 0 °C does not rule out individual cold spells or short-lived ice, but it argues against the sustained, reliable deep freeze that dragging multi-tonne stones across a river would need. On this proxy evidence, an ice-covered Avon load-bearing enough for sarsen transport looks like the exception rather than something that could be counted on.

Glacial transport of the stones themselves is a separate and much earlier question, belonging to the last glaciation many thousands of years before this window opens; it isn't addressed by this dataset one way or the other.

No coherent climate catastrophe, and no population-ending event

The most-cited candidate for a climate-driven population collapse in this period is the "4.2 ka event," dated to around 2200 BC. Roland et al. (2014) tested this directly against the British and Irish peat record and found no regionally coherent, prolonged shift to wetter or colder conditions at that date — the four records that do show any change disagree with each other in timing, duration and structure. The one genuine regional exception is a centennial cold interval in eastern England dated to roughly 4320–4210 cal BP, identified from lake isotopes at Diss Mere and independently from tree-ring isotopes in the Fenland — real, but local to eastern England, about a century long, and not an island-wide catastrophe. Nothing in the compiled proxies supports a climate event severe or widespread enough to end a population.

The climate was not very different from today's

The pollen-based reconstruction (Mauri et al. 2015) gives four millennial temperature and rainfall estimates for the Wessex grid cell containing Stonehenge, referenced against the Boscombe Down climate normals — the nearest long Met Office record. The central estimates:

Slice	Annual mean °C	July °C	January °C	Annual rainfall mm
5050 BC	9.6	17.4	2.7	~730
4050 BC	10.1	16.7	4.2	~815
3050 BC	9.6	16.7	3.8	~870
2050 BC	9.6	16.5	4.0	~840
Boscombe Down, 1971–2000	9.85	16.75	4.0	736
Boscombe Down, 1991–2020	10.42	17.1	4.6	783

Every one of the four central annual-mean estimates sits within half a degree of the modern 1971–2000 average, and all are a little cooler than the current (1991–2020) average — Wessex has warmed slightly since, rather than the Neolithic and Bronze Age being markedly colder than today. Including the full published uncertainty (±1σ, propagated across the window), the plausible annual-mean band is roughly 8.6–11.1 °C: comfortably straddling both modern baselines. Winters may have run a little cooler in the earliest slice (5050 BC: ~2.7 °C January vs 4.0–4.6 °C today), but by the Beaker period the estimate is close to indistinguishable from now. Rainfall is centrally similar to modestly wetter than today, with an uncertainty band wide enough to include "about the same." None of this supports either an unusually harsh or an unusually benign climate: mid-Holocene Wessex was, within the resolution these proxies allow, a maritime temperate climate much like the one standing at Stonehenge today.

Full series, citations, archive links and uncertainty notes for every proxy are in the interactive viewer.