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400 ppm and the rising cost of climate change / Meredith Fowlie, Energy economics exchange, Energy Institute at Haas blog, 20/05/2013http://energyathaas.wordpress.com/2013/05/20/400-ppm-and-the-rising-cost-of-climate-change/Last week brought some sobering news from the Mauna Loa Observatory where the Keeling family has been dutifully recording atmospheric concentrations of carbon dioxide since 1958. On May 9, measured concentrations surpassed 400 parts per million (ppm). Of course, from a scientific perspective, there is nothing particularly significant about the number 400. But cognitively, round numbers have an ability to attract attention as symbolic –and in this case, unnerving- milestones...