Update: According to the BP Statistical Review 2019, the Netherlands emitted 196 Mt CO2 in 1990 and 203 Mt CO2 in 2018. So they have their work cut out for them. A 25% drop from 1990 would be 2020 emissions of 147 Mt CO2, so it's actually a 28% drop from 2018. That seems near impossible.
Watching this, it seems to me that the ruling was made on the basis of Dutch civil law, not on their adherence to the European Convention on Human Rights. But I'm not lawyer and would be happy to hear from anyone who is, or others here who followed the verdict better than I did.