Dr. Joeri Rogelj:

Ultimately, as Professor Thorne and several others highlighted, methane has a relatively short atmospheric lifetime of 12 years meaning that what is currently in the atmosphere is basically the result of what has been emitted over the past 30 years. This means that the emissions that were emitted over the past 20 or 30 years are the key contributors to the current rise in concentrations or heightened concentrations in the atmosphere. We have a net zero target. Call it the climate neutrality target or as in Article 4 of the Paris Agreement, a balance between sinks and sources. It is basically a net zero greenhouse gas target. If you measure or calculate what net zero means in a different way, it will have a different implication for the global climate and the global temperature. Scientifically, that is very simple and clear. Politically, it is something one needs to confront and talk about honestly. Just saying that we are going to define the net zero target with GWP* would result in a weakening of the EU climate ambition.

The other point I wanted to make was about how using GWP* without accounting for the starting point would basically reward historically high emitters. If you start calculating GWP* from today, you basically calculate how much you start reducing from the recent past, for example, 20 years ago. It really depends on how much you were emitting 20 years ago whether you will be getting an emissions target or whether you will be punished in the eyes of GWP*. In terms of physics, there is no controversy there. We all understand that but in terms of fairness and equity, there is a big discussion to be had. That is the point I wanted to highlight.