Wow! The Washington Post is reporting this morning that the Discovery Channel has purchased the popular environmental blog Treehugger, and that “industry estimates put it at around $10 million.”

Treehugger has roared to popularity (almost 1.5 visitors each month) with a postive and empowering message about nature protection and pollution control.

The Treehugger team takes it for granted that their readers know that environmental trends aren’t good. So rather than discouraging them with a parade of bleak news, the bloggers focus heavily on what readers can do around the house and how they can save money and make a difference with smart consumer choices.

This chart above, from web information company Alexa, is interesting. It shows that over the over the past couple of years, Treehugger’s feel-good approach and Greenpeace’s feel-bad approach have both produced strong growth online. Meanwhile, the restrained and thoughtful folks at NRDC — who try to make you think instead of feel — have failed to see dramatic growth. In fact, they have been moving in the wrong direction for the better part of this year.

And if you’re still wondering whether blogs are just a fad… well… it looks like Discovery Channel has made up its mind about that.