Almost every day, Vanessa Wilbourn looked forward to a cup of tea from Starbucks on her drive to high school.

Then several weeks ago, she started wondering about whether her habit was good for the Earth. After watching a TV show about practical ways to become environmentally conscious, she decided to start small.

Wilbourn switched to making tea for herself in a ceramic mug on most days. That action saves paper cups, cash and carbon dioxide emissions from her PT Cruiser.

She also has altered other routines.

"Changing my car would be too much, but using canvas bags at the grocery store or buying organic foods or using one water bottle, I can do that," said Wilbourn, who lives in San Diego. "If everyone did that, we wouldn't be 100 percent better off, but it would make a huge difference."

Wilbourn, 17, is so caught up in the green fever sweeping the nation that she and a friend are planning an environmental rally for teens in April. These days, everyone seems interested in causing less damage to the local and global environments - even if they aren't sure what all that means.

"It's not seen as this small group of tree-huggers," said Katie Shultz of Lakeside, Calif., a public relations consultant for a health group building a green clinic in San Diego. "It's now more of a social norm to do something good for the environment. Everyone is trying to figure out how this fits into their life and business."

It's difficult to define this brand of modern environmentalism, partly because so many people have put their own spin on it. Traditional powerhouses like the Sierra Club are now joined by Wal-Mart, pastors, fashion designers, taxi companies, chefs and conceivably everyone else in exhorting the country to live green.

The new ecologists are guided by a principle that goes something like this: Meet the needs of today without compromising the ability of future generations to meet their own needs. That means reducing all kinds of waste by, for instance, using less water, electricity and gasoline.

Reasons for the "eco-awakening" are complex, say environmental experts, community leaders and everyday citizens. They often link the green phenomenon to a growing sense that the United States does not have an unlimited supply of water, fuel, trees, landfill space, farmland and other natural resources.

"There are more and more of us living in greater proximity and we are using more and more resources. That is impacting our day-to-day lives," said Todd Katzner, conservation director for the National Aviary in Pittsburgh.

Some Americans also are trying to go green because they realize their nation has a huge effect on the world, from its forests to its oceans.

"People are becoming a little bit more aware of what they might lose," said Susan Clayton, a psychology professor who studies natural resource issues at The College of Wooster in Ohio. "Of course, you value something more when you realize that you might not always have it."

Others are making lifestyle changes because they don't trust government officials to respond quickly to ecological problems such as climate change.

And in the bastion of capitalism, swelling ranks of entrepreneurs figure they can make money by selling green goods.

Residents across the nation are adding to the green momentum.

One is Joe Vecchio, 53, a community relations director for the San Diego Arthritis Medical Clinic. The self-described skeptic didn't think much about the environment for most of his life.

"It wasn't on my radar," Vecchio said.

Then, like millions of Americans, he became intrigued by the global warming documentary "An Inconvenient Truth." Vecchio watched the film in 2006, before it garnered an Oscar and before its star, former Vice President Al Gore, won the Nobel Peace Prize.

Vecchio then read extensively about environmental issues. His conclusion: "Even if this whole thing is a hoax, what's wrong with cleaning up your mess?"

Thanks to the movie and a series of major scientific reports last year, people like Vecchio now link all sorts of issues to climate change. These include environmental problems, national security concerns, food shortages, disease outbreaks and natural disasters.

He decided to share his new passion by helping to form Home International. The small, nonprofit environmental group promotes low-cost ways to live green and sponsors projects such as an annual environmental video festival at the University of California San Diego.

"Everyone sits around waiting for someone else to do something," Vecchio said. "I felt like I was compelled to do it."

On a more personal note, Vecchio said he has cleaned up his act by combining several errands on each car trip, flushing his toilet fewer times - "Don't ask," he said - switching to high-efficiency light bulbs and reusing his shopping bags.

That's where Trudy Balestreri of Chula Vista, Calif., comes in. The social worker started her conservation career in 2007 when she began noticing plastic supermarket bags everywhere, even while on vacation in Hawaii.

"I came across a landfill in Maui, and it was buried in (them)," said Balestreri, 50.

The sight made her think about her own habits. When she couldn't find any reusable sacks that matched her style, she and her sister, Trina Koller of San Diego, decided to design and market their own.

Green World Bags, launched late last year at greenworldbags.com, offers reuseable sacks for all kinds of shopping. The sacks come in trendy colors and designs and are sold online in packs of four for $19.95, a price that Balestreri said customers don't hesitate to pay.

"We are not only developing a product but an idea - a movement," Balestreri said.

"It just seems like it takes a long time for the government to make real changes in policy or for corporations to do the same," she said. "Even if this business doesn't go, we are going to make it a point to tell our friends and family to make a small difference."

But the desire to make a difference isn't always enough.

In a national poll conducted in December by GfK Roper, almost one-third of the respondents said they felt guilty about not living a more sustainable lifestyle. Nearly half of those surveyed said they would make a New Year's resolution to do something environmentally friendly.

As anyone who has made a New Year's resolution knows, good intentions don't always translate into action.

"It's not that (people) are being hypocrites," said Clayton, the psychologist. "It's just that they are not thinking through the consequences of their actions. Their beliefs are still real; they just don't always guide their behavior."

Sometimes a shortage of money or time gets in the way. Sometimes people set limits on how much convenience they want to sacrifice. Sometimes being green simply isn't the top priority.

Fred Maas, president and CEO of Black Mountain Ranch, has watched customers make telling choices when they pick out homes at his Del Sur development in northern San Diego.

"It's unfortunately true that if you present home buyers with a solar system or granite countertops, they will always defer to the granite countertops because they can see them and touch them," he said.

Maas said the dynamic is changing as conservation devices prove their financial and practical value.

"In 10 years," he said, "we won't even be having this debate because these sustainability programs ... will be embedded into everything we do."

One of the people banking on the financial rewards of conservation is Andrea Rich, 60, of San Diego.

She recently decided to dramatically reduce her water use by replacing her front lawn with synthetic turf and installing water-efficient appliances.

Rich figures the turf - which cost about $3,500 to buy and install, after rebates - will pay for itself in three years. She also said her efforts will help the region get through the current water crunch.

But don't call her an environmentalist.

"It's just common sense," Rich said. "You have to be concerned with your area of the world."

Denise Davidson contributed to this report.

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