Nature Climate Change 2, 53–57 (2012); published online 11 December 2011; corrected online 6 March 2012.

In the version of this Letter originally published, the affiliation for M. Mena-Carrasco should have read: Department of Environmental Engineering, Universidad Andres Bello, Santiago, 8370251, Chile. This error has been corrected in the HTML and PDF versions of the Letter.