Immigration means people which are going to regularly travel long distance in order to visit their relatives in their home countries. The recent explosion of migrations toward the 1st world countries coincide with an explosion of plane travel, which greatly contributes to global warming and pollution.
Furthermore, it has been shown (*) that people living in 1st world countries have a lifestyle which create more carbon emissions than people living in poorer countries. As such, immigrant in 1st world countries adopt the lifestyle of people already living there, creating further carbon emissions even when they're not visiting their home country, just because of the change of their lifestyle.
So in all logic, Green party members should be against immigration, except they aren't, at least not in my country (Switzerland). On the contrary, they are systematically fighting against nationalists who wish to reduce immigration. Why is that so ?
(*) I already know I'll be scolded for saying "it has been shown" providing sources, but unfortunately I don't remember where I got that from. It was something like, "in this country, people needs 4 planets to live, but in poorer countries they need less than 1 planet". Whenever I find a source on that, I'll edit this question.
PS: I'm talking about legal, economical migration, NOT about refugees. In all logic refugees are less likely to travel back to their country (because they'd be persecuted if they'd do so) so there's no reason to be against them migrating, in an ecological point of view.