In a recent commentary in Nature Geoscience (open access), CICERO-researcher Glen Peters argues that trying to determine the unique carbon budget for 1.5°C is a futile exercise, as uncertainties out of our control will dominate. According to Peters, the main problem is that there is no one budget telling you how much you can emit before we pass for example 1.5°C warming. There are many of them!
To say something about the future, researchers run models. These models generate pathways showing an estimate on how global emissions have to evolve over the course of the century for us to keep global warming below 1.5°C.
The problem is that there are many models and many pathways. This complicates things. Have a look at the pathways below.