Professor Valérie Masson-Delmotte:

It is important to have CO2 to one side and maybe the other gasses on the other side and so try to avoid ambiguities in metrics.

That is one point. I have also been exposed during the IPCC conference on cities and climate change science to examples of cities that implement a carbon budget at the city scale. I think it is the example of the city of Oslo in Norway that is a long way forward compared with other non-state governments in also using a carbon budget that is voted each year, together with a spending budget.