Unit 2: Externalities associated with global warming: Penguins

Climate change and the resulting melting ice caps in Antarctica are affecting the breeding patterns of penguins, according to this BBC video clip
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< http://www.bbc.co.uk/mediaselector/check/player/nol/newsid_7130000/newsid_7137800?redirect=7137853.stm&news=1&bbram=1&bbwm=1&nbwm=1&nbram=1&asb=1 >

a) In what way is the efect on the penguins an example of a negative externality?