Mark Tercek left Goldman Sachs after a long and successful career midway through 2008, just before the global financial meltdown. Good timing, except that Tercek moved on to become the president and CEO of The Nature Conservancy, the world's biggest environmental organization, as the global climate crisis is intensifying.

He feels the pressure. There's more work than ever to do, and money is tight at the conservancy. "This is really hard," Tercek told me recently. "What a responsibility we have to get this right."

Mark Tercek.
Mark Tercek

By "this," Tercek means climate change policy in general and REDD in particular. REDD stands for Reducing Emissions from Degradation and Deforestation, and it's an absolutely crucial strategy for dealing with climate change that requires slowing the growth of agriculture, forestry and cattle ranching to protect forests in places like Indonesia and Brazil. Because tropical forests are being degraded or cut down at an alarming rate, Indonesia and Brazil are ranked No. 3 and No. 4, respectively, by some studies when it comes to carbon emissions, behind the U.S. and China  but ahead of Japan or Germany. Deforestation could account for as much as 25 percent of emissions, these studies show.

The fundamental idea behind REDD is to get businesses and governments in richer countries to help finance sustainable livelihoods for people in poor countries so they don't have to cut down trees to earn a living. While it takes some doing to get your head around the idea that Americans and Europeans will pay poor people not to cut down trees, some countries like Norway are already big backers of REDD and companies like Dell and Marriott  are working with enviros like Conservation International to preserve forests in Madagascar and Brazil. The Nature Conservancy has for more than a decade been leading a project to protect 1.5 million acres of tropical forest that were threatened in Bolivia. The conservancy says the project "is expected to prevent the release of up to 5.8 million tons of carbon dioxide over the next 30 years," while preserving biodiversity and protecting communities.

"There's no higher priority for me at The Nature Conservancy than REDD," Tercek says. "We're extremely confident it can work, which is not say that it's easy." In fact, there are tricky technical, political and governance isues around  REDD, as this post on the conservancy's blog, Cool Green Science, explains. How, for instance, after paying people not to cut down trees do the financial types make sure they get the sequestered carbon they have paid for? The answer is, essentially, satellite photography, but trust me, there are other, more complicated issues.

Give his experience as a deal-maker, Tercek would seem to be the right man to help figure all this out. Mark, who is 52, grew up in a working class neighborhood of Cleveland. His first exposure to business -- as a paperboy for the Cleveland Plain Dealer -- gave him an opportunity to win a scholarship to the Western Reserve Academy, an elite prep school. (He is a loyal alum who has been president of its board.) From there, he went on to Williams College, did a stint in Japan with Bank of America, picked up an MBA at Harvard Business School and found a home at Goldman, beginning in 1984. "I liked investment banking, every minute of it," he says.

In 2006, Tercek was put in charge of the Goldman's new Center for Environmental Markets by Hank Paulson, who was then Goldman's CEO and the board chairman of The Nature Conservancy. Paulson wanted the bank to turn environmental issues into a business opportunities, which is why he put a commercial banker like Tercek in charge. For his part, Tercek got a crash course in climate change, which only intensified his interest in the environment. That had taken root when he and his wife, Amy, took their four children on nature trips to places like Costa Rica, Belize and Tanzania.

"If you see the wonders of nature through the eyes of children, you'd have to be a real dolt not to step back and think about, 'what kind of world are we going to leave them?' " Tercek says.

The Nature Conservancy job puts him in a position to have a big impact. The conservancy is by far the world's biggest conservation group, with an operating budget of nearly $500 million, about 3,600 employes including hundreds of scientists, and chapters in all 50 states and 36 countries. Unfortunately, the group, like other NGOs, has suffered during the current recession, and so Tercek has overseen the layoffs of about 10 percent of the staff. He's also got to balance the needs of the state chapters, which raise most of the money, and the global operations, where the needs for conservation are greatest.

The financial crisis, Tercek says, has been "a huge reminder that we don't have unlimited resources. We have to be really disciplined about identifying our highest priorities, and making sure they are fully funded not only with money but with talent."

Measuring trees in Bolivia as part of a sustainable forestry program.
Measuring Trees

Tercek is looking to build alliances with other NGOs -- the Nature Conservancy has joined the U.S. Climate Action Partnership, for example -- as well as with business. Corporate backing for both the voluntary and regulated carbon markets, for example, will be essential to save forests.

"I believe we can harness the power of business to solve big issues," Tercek says.

Mark spoke at FORTUNE's Brainstorm Green conference about business and the environment while at Goldman in 2008, and I'm pleased to say that he will be back again in 2010, this time representing The Nature Conservancy.

Photos CC-licensed by Flickr users Sam Beebe / Ecotrust and nbonzey.