Fig. 2: Examples of polar species with unique adaptations.

More extensive details of adaptations with associated references in Supplementary Note 2. A Polar bears have a modified cardiovascular system allowing them to tolerate chronically elevated levels of serum cholesterol in their diet. Photo from BAS photo library. Photographer Angelika Renner. B Antarctic sea spiders are examples of polar gigantism. Photo from BAS photo library. Photographer Dave Bowden. C Antarctic diatoms produce ice antifreeze proteins to survive in sea ice. Photograph from Thomas Mock, University of East Anglia. D Copepods accumulate lipids (up to 70% of individual dry weight) to survive Arctic winters. Photograph from Kim Last, Scottish Association for Marine Sciences. E Antarctic springtails survive down to −30 °C via rapid cold hardening. Photo from BAS photo library. Photographer Pete Bucktrout. F Icefish are the only vertebrates that lack haemoglobin. Photograph from Gianfranco Santovito, University of Padua. G Antarctic endolithic communities in rock survive the most extreme conditions. Photo from BAS photo library. Photographer David Wynn-Williams. H Krill has the largest biomass of any wild animal on the planet. Photo from BAS photo library. Photographer Pete Bucktrout. I Arctic tern undertakes the longest migration on Earth. Photo from BAS photo library. Photographer Callan Duck. J Antarctic nematodes normally live in temperatures of down to −7 °C, but some can survive at −80 °C. Photograph from Kevin Newsham, British Antarctic Survey. K Arctic Bell-heather thrives in deep snow over winter. Photographer from Melody Clark, British Antarctic Survey. L Polar cod shows convergent evolution of antifreeze glycoprotein to survive the cold. Photograph from Till Luckenbach, Helmholtz Centre for Environmental Research—UFZ. M Blue mussels and macroalgae can survive to 36 °C in the Greenland intertidal. Photographer Jakob Thyrring, Aarhus University. N Ectomycorrhiza colonise plant roots and play vital roles in protecting the plant from extreme conditions. Photographer Kevin Newsham, British Antarctic Survey. O An Ocean quahog holds the record of the longest-lived animal on Earth. Photographer Al Wanamaker, Iowa State University. P Antarctic fur seal genomics is revealing signals of past hunting pressures. Photographer Joseph Hoffman, University of Bielefeld. All photographs published with permission and all supporting imagery from the BAS Image Collection is published according to the image rights agreement between each photographer and the British Antarctic Survey.