Photographs of palaeoecological proxies discussed in the text: (A) tree rings, Pseudotsuga menziesii, Montana, USA; (B) pollen, Pinus contorta-type, Yellowstone, USA; (C) plant macrofossil, cf. Sequoia, Idaho, USA; (D) phytolith, Festuca viridula, USA; (E) charcoal, Idaho, USA; (F) dung fungal spore, Sporormiella, Wyoming, USA; (G) diatoms, Campylodiscus, Wyoming, USA; (H) lake sediment core, Wyoming, USA. Scale bars are 20 μm except where otherwise noted.

Pollen, charcoal and Sporormiella diagrams for Lynch’s Crater. The interval during which Sporormiella declined and charcoal first increased is shaded grey. A large shift in vegetation from a rainforest to sclerophyll assemblage is evident in the millennia following Sporormiella decline and charcoal increase.

Palaeoclimate records and anthropogenic indicators compared with global biomass burning reconstructed from sedimentary charcoal records. Globally fire was low at the beginning of the Holocene and increased during the Holocene (panel G). This trajectory is consistent with the global increase in temperature through the glacial-interglacial transition (panels A and B).