I identify as an environmental apocalyptic. It started when I was a teenager and I realized how destructive we are. It seemed clear to me even then that we were headed for disaster if we didn't learn to live in harmony with Nature.

From that POV let me address the similarities and differences to religious apocalyptics as I see them:

> There is a huge impending end of the world catastrophe coming soon...

That's what it seems like to me, but not because I was raised in a religion that teaches that, but rather because I can see with my own eyes that we are doing things like: washing away topsoil, causing "dead zones" in the ocean with agricultural runoff, poisoning the air in a few different ways (ozone, CFCs, lead, smog, etc.), over-fishing the oceans while filling them with plastic debris, and so on.

It's not the absolute end of the world, life will go on, and probably humans will survive too, but it seems clear to me that our complex global civilization is undermining the ecological foundations we rely on to the point where there is serious risk of a global collapse.

> ...because so many people are living their lives wrong,

Yes, but again, not "sin", just foolishness. And even that foolishness is understandable: until very recently it was fine to pollute because our impact was small compared to the whole of the planet. That's changed.

> the only way to stop or change that is to make massive personal changes in your life

This is a point of divergence from the religious folks. It seems to me as a non-religious person that much of religion is about controlling other people. I don't want to control other people, except to limit (what I see as) the harm they do to the environment.

We don't actually have to change our lifestyles that much to live in ecological harmony, but we do have to avoid waste and pollution. But really that's just common sense, eh? I don't have a dogma, I don't mind if you don't like camping, but I don't want the forest torn down to make shopping malls and parking lots. I don't want to breath poison. We can have nice things without destroying the environment.

> do everything within your influence to convince everyone you know to change their lives or else the end is nigh!

Here the resemblance or analog between religious and environmental apocalyptics is probably the greatest. If you believe (as I do) that there is a great risk and that we need to change some of the things we do to avert it, then yes, you want people to get on board and to spread the word.

> It often seems as well they are less interested in figuring out actual realistic solutions to these problems than feeling smugly superior because they are "one of the chosen".

This is where the difference is greatest I think. I've met a few "holier than thou" folks who are smug about it, but most environmentalists I've met personally are nice people who like Nature and don't want to mess it up. And we're totally interested in figuring out actual realistic solutions to these problems! That's like, the main thing, yeah?

The idea of being "one of the chosen" makes no sense to an environmental apocalyptic: there are no chosen, we're all going to be fucked if the shit hits the fan.

So there it is: environmental apocalypticism resembles religious apocalypticism but differs in that it's largely based on real-life events rather than a received metaphysical worldview. Religions are self-perpetuating, in contrast the goal of the environmental apocalyptic is actually to solve the crisis and, as a side-effect, obviate the apocalypticism itself. Ideally environmental apocalypticism is self-extinguishing.