climate canary

noun
  1. a human being or other living organism whose lack of health indicates environmental problems, reminiscent of the way in which live canaries were once used to detect the presence of poisonous gas in coal mines
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012