Economists are trying to figure out what the true cost of a tonne of carbon really is.

As the costs of climate change rise, economists have been revisiting a little-known but potentially profoundly important number that affects the way the real-world cost of climate change is understood. These changes are putting the wheels in motion for stronger policies in the US to meet its target to cut emissions by 50-52%, compared with 2005 levels, by 2030.

 The number in question is known as the Social Cost of Carbon (SCC). It was once dubbed the "most important figure you've never heard of" by its creator Michael Greenstone, the former chief economist under the Obama administration. 

 Read more