Defining Sustainability: Who Can Solve the Discord on the Taxonomy Regulation?

The European Union made a clear commitment towards fighting climate change and established a binding target of climate neutrality by 2050. Towards this goal, the Union is mainstreaming climate change in all Union policies and the Taxonomy Regulation adopted in 2020 is a good example of this phenomenon and a perfect candidate to study the boundaries of climate mainstreaming. It notably raises the question to which extent the EU legislator and the Commission have the possibility to shape the definition of what is sustainable when it comes to climate. Are limits to be find in the Treaty or the jurisdiction of the Court? This is particularly salient with the inclusion of nuclear and gas in the Taxonomy in a context where the Member States have contradictory views and interests on what should be sustainable and threaten to contest the decision in front of the Court. In the latter event, would it be to the judges to define the contour of sustainability, or shall they refrainfrom doing this?