Matt Ridley notes in respect of the Paris Treaty on Climate change that:
….. the economist Bjorn Lomborg calculated how much the pledges would reduce warming, using standard models and generous assumptions about how quickly the reductions would be achieved and how long they would be sustained.
He found that all the promises made by the US, China, the EU and the rest of the world, if implemented from the early 2000s to 2030, and then sustained through the rest of the century, would reduce the expected rise in global temperature by only 0.17°C in the year 2100. That is to say, instead of rising by 2, 3 or 4 degrees or so by the time our great grandchildren are adults, world average temperature would rise by 1.83, 2.83 or 3.83 degrees. Lomborg put it this way: “Current climate policy promises will do little to stabilise the climate and their impact will be undetectable for many decades”. A different study by scientists at MIT came to similar conclusions. The INDCs add up to the square root of zilch.
However, and this is the crucial point, Lomborg also points out this invisible achievement would come at a staggering cost, somewhere between $1 trillion and $2 trillion a year: “Paying $100 trillion for no good is not a good deal”.