Don't know about membership requirements, but countries which adopt an ETS-style scheme can be exempted from the EUcarbon tariffs. It's a smart mechanism.

Could be a stepping stone?

EU CBAM will accomplish that by design.

📌

So between the Trump admin's domestic focus and the lack of direct backchannels to Trump himself, US allies in Europe and Asia may find themselves listening to busy signals and "Sorry, wrong number" recordings for a good part of early 2025.

/Ends