From Reuters (Climate change inaction will cost trillions):
Failing to fight global warming now will cost trillions of dollars by the end of the century even without counting biodiversity loss or unpredictable events like the Gulf Stream shutting down, a study said on Friday.
But acting now will avoid some of the massive damage and cost relatively little, said the study commissioned by Friends of the Earth from the Global Development and Environment Institute of Tufts University in the United States.
The study said the cost of inaction by governments and individuals could hit 11 trillion pounds a year by 2100, or six to eight percent of global economic output then. ... By contrast, spending just 1.6 trillion pounds a year now to limit temperature rises to two degrees could avoid annual economic damage of around 6.4 trillion pounds, the Tufts report said.
Here is the report: Climate Change - The Costs of Inaction [*.pdf].
Hat tip: Daily Grist.