Fig. 2: Southern Scandinavian regional climate, sea level and coastal environment during the Holocene thermal maximum and human response.

Environmental variables: a Pollen-inferred mean annual air temperature based on a sediment succession from Lake Trehörningen³⁷, southwest Sweden and examples of warmth-demanding indicator species present during the Holocene thermal maximum (HTM), but absent/rare in Danish waters today (see Supplementary Fig. 21). b Diatom-inferred salinity expressed as deviations from modern salinity for five Danish coastal sites. Order of box plots from left to right: Kilen, Horsens Fjord, Norsminde Fjord, Tempelkrog, Sebbersund (repeats for each time period). c Sea level, Blekinge, southeast Sweden³³. Ecological and human response variables: d Total sedimentary pigment accumulation rate z-scores with lowess smoother (span 0.1) for three Danish coastal sites (Kilen, Horsens Fjord and Tempelkrog). P1 and P2 refer to periods of pre-agricultural marine production increase across Southern Scandinavia. e Summed probability distribution (SPD) of ¹⁴C-dates on shells of the European flat oyster (Ostrea edulis) from Danish shell middens as a proxy for total midden abundance and marine resource availability (see text and Supplementary Note 2). Black line indicates expected probability distribution. f Population density proxy for southern Sweden, Jutland and the Danish islands during the mid-Holocene⁷. g Cumulative number of technologies used to exploit the marine environment over the study period^{44, 65} and agricultural technology post 5900 BP. 1. Fish trap; 2–4. Lance, dugout canoe, paddle; 5–7. Fish hook, leicester, paddle; 8. Fish net; 9. Polished flint axe; 10. Ard. (see Supplementary Table 5). h Land-use/agricultural change indicators: sediment accumulation rate (SAR) and percentage of non-arboreal pollen (NAP), Plantago lanceolata (ribwort plantain) and cereal pollen at Lake Gudme Sø⁴⁸, Funen, Denmark. i Isotopic analyses of δ¹³C, δ¹⁵N and δ²H data from Mesolithic and Neolithic humans and dogs showing shift from a predominantly marine (more positive values for all isotopes) to terrestrial diet (more negative values)^{10, 47}. All box plots (in b, i) show maximum, minimum, interquartile range and median. Cultural divisions after Fischer and Kristensen⁸; MNA, Middle Neolithic A; MNB, Middle Neolithic B; LN, Late Neolithic.