Totally missing the point
The environment is important. Maybe it doesn’t look like it, but every little action helps in the grand scheme of things. Environment-friendly disclaimers at the beginning of emails help too, but only when they are at the beginning. It also helps when they are noticeable.
Putting a small, almost invisible disclaimer at the end of an email isn’t really the best way to go. And if you need this email printed out, you will end up with one piece of paper with only the disclaimer printed out on it.