RS: We start with an explanation of the term "ecosystem capital."ROB JACKSON: "Ecosystem capital, or maybe put differently - ecosystem services - are the value of what we get from natural systems. For instance, a city such as New York City can spend a lot of money to build a sewage treatment or water treatment plant. Alternatively the city might buy a thousand or five hundred thousand acres, whatever the value is, of land and use natural capital, natural services, to cleanse that water for us.

"That is, in fact, what New York City did some years ago, saving hundreds of millions of dollars. So you allow nature to do the work for you, and then you find a way to put an economic value on that work. And that's where the term ecosystem capital comes from."RS: "Another phrase that was thrown at me was -- we need to be looking at our ecosystem services, as you say, and not as much at 'charismatic mega fauna.' [laughter]"ROB JACKSON: "Yes. Charismatic mega fauna are the large, sexy mammals that people like to watch. So that might be an elk, a bear, a wildebeest in Africa, an elephant -- "AA: "Polar bears."ROB JACKSON: "Polar bears is another great example. So we tend to focus on these large animals and we often tend to manage and set up preserves for these large animals. And those animals are charismatic -- they're pretty, they're nice to look at, but they're often not the animals that provide the ecosystem services that we value most."RS: "And the point I understood was that we should be looking at our undervalued ecosystems -- or we should value our ecosystems more in comparison."ROB JACKSON: "That's right. One of the problems with our current economics is that we don't do a good job of putting a value on the services that we get from nature. So it's easy to assign a value to what a power plant uses or produces, or to what a sewage treatment plant cleanses our water. It's not easy to put an economic value on what nature does for us.

"Plants cleanse our air. The soil cleanses our water. But that cleansing, that purification and all the many resources that we get from nature often fall outside our accounting system. And so we're just simply not very good at taking into account what nature gives us."AA: "Now one of the services that nature provides us, obviously, is food, and that brings us to another term that we're hearing a lot lately, which is 'food miles.' Why don't you define it."ROB JACKSON: "Well, sure. This is one for me that's pretty new, but food miles are the number of miles that food travels before ending up on your plate, and that the higher the food miles the greater the environmental cost associated with the food -- how much energy was used to transport that food to actually put it in front of you and me."RS: "Now, I think the importance of these terms is to raise awareness."ROB JACKSON: "I agree with that. But they also, I mean they are -- I know that they do sound jargony and some of them are jargony. But there are, for some of these at least, fairly specific meanings. And, in fact, in the scientific community, some of these terms have much narrower meanings than come to be the meaning in just common usage."RS: "Can you give us an example?"ROB JACKSON: "Well, let's start with maybe the most basic example, just the word 'ecology.' I think when you walk up to someone on the street and ask them what ecology means, people will bring up recycling and sort of saving the environment, saving the planet.

"As a science, the field of ecology studies how plants and animals and organisms interact with the environment around them. It has a much narrower sense and really doesn't say anything about recycling or about environment stewardship. But it has come to be viewed as saving the planet because many ecologists, myself included, really care about the environment and valuing the environment."AA: "And 'sustainability,' which will be our final term, if you could maybe explain that."ROB JACKSON: "Sure. Sustainability is another one of these words that has kind of a life of its own, a lot of different meanings. But the idea is that we need to think about long-term consequences of how we live and how we manufacture things. So are we building something in a way that will allow people in fifty years or a hundred years or a decade to build the same product in the same way? Or are we using a resource in an unsustainable manner, are we polluting a body of water or are we polluting air in a way that will cost people down the road?"RS: Rob Jackson is a professor of biology and environmental sciences at Duke University in Durham, North Carolina. You can hear the first part of our discussion on the Wordmaster website at voanews.com/wordmaster.

AA: And that's Wordmaster for this week. Our e-mail address is [email protected]. With Rosanne Skirble, I'm Avi Arditti.