You may've recently heard the term "carbon offset." That's the idea of negating – or offsetting – the greenhouse gasses we put into the atmosphere. So, if you drive or fly a lot, or just use a lot of electricity, you can offset your pollution by investing in projects like building wind turbines or planting or preserving trees. Healthy forests help fight global warming and climate change because trees remove the key greenhouse gas carbon dioxide from the air. It's estimated that 20 to 25 percent of carbon dioxide emissions today come from the cutting down and burning of forests, mostly in the developing world. The World's Jason Margolis looks at a project in Central Mexico, where leaders are trying to preserve a forest the size of Rhode Island. But they need foreign dollars to do it.

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Margolis: The road heading northwest out of Mexico City is a flat boring landscape. The monotonous brown horizon is broken by an occasional purple blooming jacaranda tree, or a small, impoverished town. Then, after about five hours of driving, the scene changes dramatically in the state of Queretaro.

Ross: "Below us we see cactus and ocotillos, and yuccas. But as we look forward, we see that there are clouds coming over the mountains, and we begin to see different trees such as oaks and pines."

Margolis: David Ross is part of a team of environmentalists trying to preserve what's called the Sierra Gorda Biosphere Reserve. It's a diverse region with ecosystems ranging from semidesert areas to mountainous cloud forests. Black bears, jaguars, and Mexican salamanders all share this space. The jagged peaks of the eastern sierra Madre peak above 9,000 feet, then plunge into dramatic sloping valleys deep below. It's called a Biosphere, not because it's domed or anything like that. It's a Biosphere because unlike, say, a national park, people privately own the land.

Sierra Gorda Biosphere Reserve

Ruiz Corzo: "So approximately 90,000 people live in this area and in order to conserve the biodiversity, we have to involve them in its protection."

Margolis: And "involving them" means environmental education. Pati Ruiz Corzo is the government appointed director of the Biosphere Reserve. She speaks to a group of elementary school children who form a circle around her. She's giving a lesson about the science of climate change in the village of Epizotes. It's a typical community in the Biosphere. A few dozen families live in small cinder block homes with corrugated metal roofs. The people survive on a basic diet of little more than rice, beans and corn.

Pati Ruiz Corzo talks about the trees

She breathes in dramatically and says the trees suck away dirty pollution. The children stare wide eyed at Corzo. She says trees make the carbon disappear. Corzo is a force of character: a short, stout woman with a warm smile and infectious enthusiasm. The former music teacher abruptly interrupts her lecture and starts singing about the forest.

Ruiz Corzo Singing: "En el lejano bosque, ya cantara el coo-coo..."

Margolis: The children giggle nervously. But after a few repetitions, all the children, and the adults catch on with the easy words and are singing about the trees.

Ruiz Corzo: "Cantamos todo, listos? En el lejano... "

Margolis: It was largely through Corzo's personal efforts that the Mexican government turned the Sierra Gorda Biosphere into a protected area 10 years ago. Back then, people say it was filthy here. There was trash in the streams and in the forest. Today, it's almost impossible to find a scrap of litter. The residents are engaged in basic environmental activities like recycling and watershed restoration. Small projects are bringing some outside financial support. But leaders here hope that the big moneymaker will be the Biosphere's forests.

In the middle of some farms is an odd site: a tiny pine forest – only a few acres in size. The young pine trees are barely taller than the surrounding corn stalks. An increasing number of farmers here are growing trees on their land. One of them is Alfredo Rubio.

Rubio: "We used to be in the business of cutting down trees to plant corn. But then about 20 years ago, we started a nursery for trees and we realized it was good business to plant trees and sell wood."

Margolis: Now he gets paid, not to cut down his trees. A Mexican foundation pays him about $8 bucks per acre, per year to keep his trees standing. Rubio's newphew, 77-year-old, Francisco Montez, is also planting trees on his farmland. He says he's not just doing it for the money, but to help the environment. He says you can see the effects of global warming right here on this land.

Montez: "50 YEARS ago we used to have droughts, but the heat wasn't so intense. Now we have really hot weather for eight days and it totally dries up the soil."

Margolis: Montez says under these conditions, it's easier to grow trees than corn. Environmentalists would like to see a lot more trees inside the Sierra Gorda Biosphere. And they're hoping that environmentally conscious individuals and companies in places like the United States will be compelled to open their wallets to help.

Brett GalimidiIn San Francisco, environmental consultant Brett Galimidi, a partner with the Social Venture Technology Group, says that means establishing a connection between the U.S. and Mexico.

Galimidi: "If you emit a ton of carbon here in San Francisco, that goes up into the atmosphere and the effects of that are cumulative and will be felt around the world. So in order to combat it, we have to have pockets all over the planet of healthy ecosystems to deal with carbon issues."

Margolis: Galimidi has also been working extensively with the folks in the Sierra Gorda. He says Americans need to be convinced why they should give their money to a Mexican farmer vs., say, helping build a new wind farm in South Dakota? Galimidi says it's all in the presentation.

Galimidi: "So from a practical perspective, what does that mean? Well it really is a lot of Numbers and a lot stories. And being able to understand how those things relate to each other. So, Gone are the days where it's here some money, I trust good things are going to happen to it. Now it's: I'm happy to give you my money, but there are a lot of people asking for my money. I want to know where this goes and what I'm going to get for it? Just like any investment, what is the return that I can expect?"

Margolis: At the Sierra Gorda Biosphere, they'll tell you what you can expect. Workers from the local grassroots organization Bosque Sustentable take a tree sample from the forest. The wood goes back to the lab, and scientists determine its carbon content. Then, workers measure the diameter of all the standing trees in an area that's been paid to be protected. That way, they can tell you almost exactly how much carbon dioxide your donation isn't going into the atmosphere because of your donation.

Measuring the trees

Now here's the controversial part. It's one thing to plant new trees. But paying people not to chop down trees that are still standing? The White House has called it blackmail, accusing people in the developing world of holding their trees hostage.

Laura Perez Arce says that's ridiculous. She works in the Biosphere with the grassroots organization Grupo Ecologico. Perez Arce walks through a barren landscape that used to be filled with Oak Trees.

Perez Arce: "Deforestation is a reality. In the developing world, here, when people have the opportunity to do work on their lands, they're seeing a future. And they're not seeing a need to maybe sell their lands, or rent it to rancher, And allow them to take down their forest or to an agriculturalist."

Laura Perez Arce

Margolis: Perez Arce says people cut their trees here for one reason: to feed their families. But she says, if keeping trees standing can serve a dual purpose –preventing the release of greenhouse gasses AND alleviating poverty – well, she thinks that's a good sales pitch. She's working with her mom, who lives in California, to try and get Americans to financially support the Sierra Gorda Biosphere. They're raising funds through their small organization, Viva Sierra Gorda. She's hoping that when people are choosing what carbon offset program to invest in, they'll say to themselves...

Perez Arce: "I want my carbon to be holistic. I'd like it to include all of the different activities that will improve the ecosystem itself, and will therefore improve the livelihood of humans and wildlife."

Margolis: Perez Arce calls this "Gourmet Carbon." And she and the other environmentalists here are hoping that sales of carbon offsets will have a residual effect throughout this whole area.

For the World, I'm Jason Margolis, the Sierra Gorda Biosphere Reserve, Mexico.

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Viva Sierra Gorda