1. Department of Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, Devon EX4 4RJ, UK
2. Environmental Change Research Unit (ECRU), Faculty of Biological and Environmental Sciences, University of Helsinki, 00100 Helsinki, Finland
3. Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, Cambridgeshire CB2 3EA, UK
4. British Antarctic Survey, NERC, High Cross, Cambridge, Cambridgeshire CB3 0ET, UK
5. Department of Geography, Durham University, Durham DH1 3LE, UK