There is a recent one currently in Aus which is both environmental and political

Actually looks like a couple:

1. NSW Labor accused of ‘fundamental breach of trust’ over logging in promised koala national park
2. Thousands of Labor members take climate challenge to Albanese

In both cases discussions are more likely to be focused on the political aspect, however would be of interest to both communities. A solution would be to have it posted to politics, cross-posted to environment and locked with link to politics post. Since you can still upvote/downvote locked posts, it wouldn’t get lost.

To get around these problems there would have to be some ordering like: politics > environment > australia > news. But it would have to become simple and obvious enough that there is very little moderation work.

To move posts do you have to crosspost, then lock or delete in the original community?

That’s what I think, though it is preferred if the OP can crosspost it so they get the interaction (replies).