Temperate to tropical palaeoclimates on the northwest margin of Europe during the middle Cenozoic

Globally, the middle Cenozoic (Oligocene to early Miocene, ~33.9–15.97 Ma) was characterized by a warmer, wetter climate than present. Reconstructing the climate of this stratigraphic interval helps us to better understand the implications of present and future anthropogenically-driven climate change in an Earth system with an established Antarctic ice mass and comparable pCO2 levels (400–700 ppm). Relative to mainland Europe, little palaeoclimate work has been done on the British Isles for this time interval. Compiled middle Cenozoic palynology records from across the British Isles were used to quantitatively reconstruct palaeoclimate, which was then used to define Köppen-Geiger signatures for each palynomorph assemblage. These reconstructions were used to show the presence of a temperate, dry-winter and hot-summer (Cwa) Köppen-Geiger climate type before 31.8 Ma, which was possibly a short-lived event driven by precessional (~26 k.y.) forcing. We attribute reconstructions with dry-winter Köppen-Geiger classifications to combined eccentricity-obliquity-precession (~405 k.y.) forcing, after the Eocene-Oligocene Transition. Declines in Mean Annual Temperature, in Chattian sections, are associated with the Svalbardella-2 and 3 North Sea cooling events. The late Oligocene warming event is shown to have produced tropical rainforest (Af) Köppen-Geiger classification types in the British Isles. Following early Miocene glaciation, a temperate, no-dry-season, warm-summer (Cfb) signature was reconstructed. We suggest the present-day climate of the northwest margin of Europe is comparable to the early Miocene palaeoclimate. Under increased pCO2 concentrations, based on projected twenty-first century anthropogenic warming scenarios, there is potential for wetter summers becoming more prevalent within the next century.