America in the Brangelina ERA does not lack celebrity advocates: Scarlett Johansson for Barack Obama, George Clooney for Darfur, Matt Damon for clean water. Whether the famous are effective advocates for good is debatable, but Madison Avenue long ago proved they are great advocates for buying stuff. Ironically, considering the tonnage of celeb-inspired purchases choking our landfills, this also makes them ideal pitchmen for the environment. After all, green issues are about consumption: what to eat, how to build your house, what junk to fill it with and how to dispose of it all.

So when Discovery Networks launched environmental cable channel Planet Green last month, it hired lots of celebs, from former St. Elsewhere star Ed Begley Jr. to Entourage's Adrian Grenier to Leonardo DiCaprio. Later this month, star chef Emeril Lagasse debuts an organic-cooking show. Battleground Earth will pair rocker Tommy Lee and rapper Ludacris on an eco-buddy road trip.

The timing is right, as movies from M. Night Shyamalan's The Happening to Pixar's Wall-E rap viewers' wasteful ways while selling huge tubs of popcorn. But Planet Green's ecotainment is also a study in what kind of Hollywood activism works and what's just noise pollution.

One of Planet Green's most promoted--and most vapid--shows is Grenier's Alter Eco, in which the HBO star and several fashion-plate friends bring eco-consciousness to the deprived world of upscale Los Angelenos. They visit organic restaurants and sip biodynamic cabernet sauvignons. They build a home compost bin for a chef from Spago and work on a "green" mansion large enough to dry-dock an aircraft carrier. And they cap off each episode by sitting down to cocktails or dinner and telling one another how awesome they are. ("Why are you such a mensch?" Grenier asks a pal.) In Alter Eco, environmentalism exists not to save the world but to ennoble people who are richer, thinner and cooler than you will ever be.

It's fitting that the smug Alter Eco's title is a twist on the word ego, because the show is a perfect marriage of sanctimony and self-regard. It's ecotistical. It's compostentatious. Grenier and company mean it to be aspirational--it's cool to be green!--but the effect is exactly the opposite. Hey, I compost and recycle too, I think as I watch. Do I look like that big a tool?

A more old-fashioned strain of high-minded celebrity daffiness shines through on Hollywood Green, which is basically Access Hollywood edited down to the stars' red-carpet prattling about their hemp wardrobes and chemical-free nurseries. (I have waited in vain for a segment on organic Botox and biodegradable implants.) Justin Timberlake builds an eco-friendly golf course. Host Maria Menounos enlists an "eco-designer" to redo her summer cabana. "Green is beautiful!" she declares. Sure it is, if you have a freaking cabana and a personal decorator.

Each of these shows believes that environmentalism will sell only if it's made glamorous. But Planet Green's better celeb shows take just the opposite approach. In Living with Ed, Begley offers tips from his home, no pimped-out eco-pad but a modest Studio City bungalow where he fusses with a solar oven and plugs in his electric car. Self-deprecating and charmingly nerdy, Begley is no dilettante, having immersed himself in low-impact living long before anyone was devoting cable channels to it. Yes, the show's concept is hokey--Begley's Green Acres bickering with his less eco-minded wife--and it relies too heavily on star cameos. But at least Begley presents his choices as being about something bigger than generating his own solar-powered halo.

The best show on Planet Green, however, succeeds in part because it has so little of its celebrity in it. Greensburg, produced by DiCaprio, is a documentary series about a Kansas town that decides to rebuild to green specifications after being nearly obliterated by a tornado. DiCaprio introduces the first episode, then steps out of the way as the show tells the story of the culture clashes, setbacks and moments of redemption that happen when a town decides to give back after losing everything.

If the Hollywood name draws viewers in, Greensburg quickly deposits them in the real world of commerce and compromise--where, after all, any meaningful change will have to take place. If you want to see that world on Planet Green, look not at the glamorous celeb shows but at the commercials--including ads for chemical bathroom cleansers and processed, nonorganic snacks. Which points out something that the channel's upscale shows could stand to remember. It's one thing to live on Planet Green when you're a star. The rest of us have to get by on Planet Earth.