I came here to post about the new Cattle Decapitation album, Terrasite. It's my favourite death metal album of the year so far, and it kind of lines up with what you're talking about jammindude.
I'm not sure about their previous work, but this album focuses on environmentalist issues and overpopulation. Similarly Gojira (who aren't straight up death metal, I know) have been writing about environmentalist issues for their whole career.
There are probably loads of others if i have a good think about. The problem is, that most death metal I don't always know what they're singing about
Anyway, everyone should check out Terrasite, I know Glasser will back me up.