The evidence for temperature changes, based mainly on pollen, is outlined in National ScARF for the period (ScARF Chalcolithic and Bronze Age section 3.1). However, the overall general picture only gets researchers so far, and it is important to build up the local picture by combining information on local climate, sea level changes and vegetation (Chapter 3.2).
The woodland evidence suggests agricultural expansion in the Chalcolithic and Early Bronze Age in general, but other environmental evidence does not suggest this was as a result of a better climate; instead, the evidence suggests a climatic decline. Nevertheless, as more well-dated studies are showing, it is likely that the varied landscape created localised and variable climatic changes across the region (Tipping et al 2008b). The climatic decline seems to have continued into the Late Bronze Age. Despite these increasingly severe climatic constraints, it remains uncertain how these constraints were reflected in settlement and land use; variations should be expected almost from glen to glen. While the large numbers of presumably abandoned Bronze Age dwellings still visible across the region do indicate general retreat away from the higher land by the end of the Bronze Age, this pattern masks complexity, and no simple explanation can be applied uniformly across time or the region.
Tephra from volcanic eruptions has been identified at some Highland sites. In the Strath of Kildonan, the impact of an Icelandic eruption c 1300 BC (Middle Bronze Age) had little effect (Charman et al 1995). At Lairg the impacts were also considered minimal (McCullagh and Tipping 1998, 208–9), and current thinking considers there to be no significant adverse effects from volcanic contamination.
While peat has formed in poorly drained basins since the end of the last glaciation (Ratcliffe et al 2019), the formation and spread of blanket peat has been both a cause and an effect of contracting settlement and land use. How much this was a Bronze Age phenomenon remains a matter for debate. It is now increasingly clear that this spread of peat was not uniform across the Highlands, where it occurred at different periods (Tipping 2008), but a detailed understanding awaits many more local studies.
Peat basins remain the primary sources of long chronologies of vegetation and environmental change. At Loch Farlary (MHG10510) in Sutherland, for example, a relatively shallow basin provided vegetational change data spanning the Holocene. In particular, it showed that locally the pine decline was not a single sudden event, and it provided a much more nuanced picture of the local Bronze Age spread of pine and its impact upon the landscape (Tipping et al 2007b; Tipping et al 2008a; Chapter 3.2; Case Study Environmental Investigations at Garbh Allt Catchment). Oliclett, Caithness (MHG29867), offers one of the most detailed chronological and spatial models for peat formation throughout the Holocene, where spreading blanket peat buried a Mesolithic lithic scatter. Human activity held the expansion of blanket peat in check on three occasions during the Bronze Age period of land use (Tipping et al 2007a). It is clear that in many areas, such as at Loch Farlary and Oliclett, the peat had already been forming when farming first took place; this provided difficult and challenging conditions with which the people of the Bronze Age lived and occasionally surmounted (Tipping et al 2007a; Tipping 2008). Current research by Hannah Genders Boyd at University of the Highlands and Islands on pollen analysis near roundhouses in Wester Ross should provide valuable insights into climate change and landscape issues in the Chalcolithic, Bronze Age and Iron Age.