As any politician will tell you, it’s one thing to get someone to smile and shake your hand and quite another to convince him to pull out his wallet. And as any brand manager will tell you, this maxim also applies to environmental marketing. Lots of consumers say they care about the planet, but try to get them to spend extra on eco-friendly brands. Marketers have puzzled over this disconnect for years. Now, a new study has proven that it’s not all in their heads.

According to “Green Brands 2011,” a survey just released by global brand consultancy Landor, consumers are worried about the planet like never before—just don’t ask them to dig too deeply into their pockets to save it.

Over half of the survey’s 9,000 global respondents said they think the environment “is on the wrong track,” and a whopping 73 percent of Americans said it’s important to buy products from green companies. But when asked how much more they’d be willing to pay for those products, 37 percent of U.S. shoppers said they’d pay nothing extra and only 33 percent said they’d fork over up to 10 percent more. (Various smaller fractions would spend higher amounts and some were undecided.)

Landor communications chief Mindy Romero says the picture is not as dire as it looks: “There’s a perception that green brands are significantly more expensive, but many of them—household products especially—aren’t a lot more than 10 percent higher anyway.”

The study also found that concern about global warming tends to take a backseat to worries over the family paycheck, which may explain some of the stinginess on the part of domestic consumers. "During the recession we saw a dip in environmental concerns," Romero said. "Now, we're coming back up to the levels we were at in 2008."

Still, Americans do look a bit cheap compared with their global brethren: Though only a third of U.S. shoppers would pay 10 percent more for a green brand, that slice of the population jumps to 44 percent in France and 48 percent in Brazil. Perhaps most telling: Asked if they’d pay over 30 percent more for an eco-friendly product, the highest number of those who would (10 and 13 percent, respectively) were shoppers in India and China.