Global Economic Cost of Climate Chaos

The Stern Review published by
the British Treasury at the end of 2006 concluded that if the more dramatic predictions come to pass,
then inaction on climate change could cost the world economy more than 20% of global GDP each year
(whereas the costs of effective action could be limited to just 1% of global GDP each year).

http://www.hm-treasury.gov.uk/independent_reviews/stern_review_economics_climate_change/sternreview_index.cfm