At 2012 rate of increase of CO2 emissions, by 2050, global warming will be as high as 5.3degC. Internationally agreed target of 2degC can be met if the world spends $1.5Trillion now on ways of reducing emissions. If we do nothing, letting things get worse until 2020, when worsening extreme weather compels action, the cost of getting back on track will be $5Trillion not 1.5, an expensive delay. Of course, this takes no account of cost of extreme weather damage.

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