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wilson: i have a lot of faith in the good sense of human beings and their desire not to destroy the world. a lot of moral ineptitude, it should be remembered, is due to poor planning rather than innate wickedness. i think people are innately good, but they tend to be terrible planners, so they get themselves into situations, then, when they do bad things. and i believe that's the situation we're in right now in the environment. people around the world are now generally aware of important environmental changes, led by climate change. they are aware that species are going extinct, and they understand that it's not a good thing if we destroy the rainforests and

coral reefs. in fact, it's very bad and dangerous thing. and this rising awareness, i think, can be read as a trend, which is a source of optimism. the question is -- will we wake up? will we reach a tipping point? and i hope there will be a tipping point where this becomes part of the global ethic in time to avoid real catastrophe in terms of climate change that'll affect all of us and, in terms of mass destruction, possibly up to half the species on earth say, by the end of the present century.

narrator: rising human population, biodiversity loss, and climate change are issues of primary environmental concern not only for our descendents but for all the species that call this the habitable planet. when environmental scientists look into the future will human actions overwhelm environmental systems, or will we work together to assure a stable environment? schrag: there's still so much about the eartsystem that we don't understand whether it's about oceans or about the climate system or about ecosystems and biology. there's still so many mysteries left to uncover. our impacts on the earth are so huge, in many ways, it's an experiment we're doing on the planet. it's an experiment because it's never been done before, and no one understands the earth well enough to predict exactly what's gonna happen.

we're gonna find out over the next century what this experiment yields and whether our actions will allow the earth to persevere in a state that allows life to flourish or whether human activities will really cause a catastrophe of some sort. we're affecting the ecs we share the earth with through the way we use land, by building cities and roads cutting down forests. we're affecting the water we drink by chemicals that we are spilling on the ground. we affect the air we breathe and most importantly we're affecting the climate all around us. but underneath all of these is the basic fact that there are more humans today than ever before and that number is growing year by year. bloom: it took the human race 99% of its history

to reach 1 billion people. it reached 1 billion people around the year 1800 and now we're adding another billion every 12 to 15 years. so, in 1960, world population stood at about 3 billion. it crossed the 6-billion mark by the year 2000. it's now over 6.5 billion. it looks like global population will stabilize in the 9- to 10-billion range within the next 50 to 100 years. that is an extraordinary challenge -- the challenge of absorbing between 2.5 and 4 billion additional people onto the planet and having the resources to feed them and to clothe them and to house them and to educate them and to provide for their medical care. the capacity of the environment to assimilate air, water and land pollution is much more strained, so the capacity of the environment to basically assimilate and recycle waste is much more likely to be exceeded.

and by any measure that challenge has earned the name "the population problem." narrator: of all future human impacts on the planet, population growth is one of the most important variables. conservative estimates of world population growth suggest that our species will demand 50% more goods and services than are currently produced worldwide. but that assumes consumption rates around the world will remain the same as they are today, which isn't the case. schrag: the population problem isn't just the number of people but also what those people do. over the next century, our population may grow to 9 or 10 billion. but more than that people are getting richer. they're using more things, more energy, more natural resources and this is putting huge stress on the earth system. narrator: world gdp rose slowly until the industrial revolution. around 1800, global economic output

began to grow faster and faster leading to dramatic impacts on the environment. schrag: when people are poor and they eat a diet mostly of grains, they need the water required to grow that grain and the land required to grow that grain. if people get a little bit richer and they start to eat meat they start to have a cow maybe a few goats. now they need not only the grain that they would eat but also the grain to feed these animals. narrator: higher-income countries require more land area to support each person than poor countries. as incomes rise, each person's footprint increases as well. schrag: and when they use more land, their footprint on the natural world becomes greater and greater, pushing natural biodiversity to exist in a smaller and smaller space and threatening natural ecosystems.

narrator: in the next century, the increased population will demand even more from the world's diminishing natural ecosystems. the tropical rainforest is one dramatic example. human needs for wood and other natural resources fueled the destruction of much of the rainforest. from 1950 to the present rainforests shrank from 14% of the planet's land area to only 6%. if this rate of decline continues, there will be no rainforest by the end of the century. schrag: and so, there remain many parts of the tropics where huge areas of biodiversity still exist, and yet, that's changing more and more. in the amazon, as we've cut down forests to grow soybeans in indonesia, as we cut down forests for timber and for palm plantations what we're seeing is natural ecosystems are threatened

by human land-use changes. i would argue very generally we should care about the health of any ecosystem -- yea, even the very sparse ecosystems of deserts or parts of the arctic. but i think we need to pay a special attention to the tropical forest because that's where most of the diversity of life is on earth at the species level. for heaven's sake, we're talking about most of the creation. do we really want to see these forests continue to be destroyed? the s th are in them are ofn millions of arold, and they've taken just almost unimaginably long periods of time to evolve to be adapted to one another and to create unique genetic combinations and unique physiology and unique life cycle. every time we allow one species to

go extinct, we're erasing a million years or so of genetic evolution and the unique products of that evolution. we're losing it often without even knowing it was ever there. dr. laurence: there's lots of reasons to care about tropical forests. obviously they're the greatest bastions of biological diversity anywhere on the planet and of course, they're producing massive amounts of oxygen, which help to keep our whole biosphere survivab they also store a huge amount of carbon in the vegetation. and so, when those forests are slashed and burned most of that carbon is going up into the atmosphere and carbon dioxide and methane and other kinds of greenhouse gases, of course which is the reason that we have the greenhouse effect. so, maybe a quarter of all the greenhouse gases that are being produced by humanity right now are occurring as a consequence of the rapid slashing and burning and razing of tropical forests. so, i think that we've really got our work cut out for us.

there's been some successes -- some new parks and reserves that have been designated, but i think we have to be very vigilant. right now, i feel like we're sort of like we've got our fingers in the dike, and, really, we're trying to stave off a potentially catastrophic flood of extinctions. pringle: when you talk about conservation or preservation trees are in some sense perhaps just the easy benchmarks that we can reach for -- we've saved this many trees. but when i think about conservation i do think about, okay, we may have saved that many trees but how many fungi have we saved underneath the trees? for every tree that you've saved, you've saved 10 species of fungi, 15, 20? we don't know. preserving biodiversity isn't a problem that belongs only to the people of the tropics. the truth is that even if you've preserved all the biodiversity in the tropics and you tore down everything in north america it wouldn't be a very fun place to live. so you need to pay attention to your local biodiversity as well as the biodiversity that exists elsewhere. and it's very hard to predict what components of biodiversity you can lo or nolose

and still have a stable ecosyem. you n arguthat on tpees being lost will have no great impact on the ecosystem but that's not what's happening. we're losing dozens or hundreds of species at a time. and although it's very difficult for us to understand the services that ecosystems provide to us, because they have no traditional economic value, they do, in fact, provide us with a tremendous wealth of goods and services, and it may be time for us to start thinking about those services and protecting them not only for ourselves but for our grandchildren, as well. narrator: using the united states as an example, new wilderness areas on land continue to be set aside. but the ocean, which covers 75% of the planet has even less total protected area than the land. pauly: on land we protect about 10% to 15%. most countries protect 10% to 15% of the forest

of the wild land and in the water, we don't protect anything, really. that is really an important thing -- that we don't protect any water area. so, put differently, we can fish on 99.4% of the ocean. so, the idea of protecting fish is counter our deepest feeling but we must protect fish if we want to have them. there seems to be a tendency when we throw our industrial might at a fish species to deplete it, and it happens everywhere you look. so, there are lots of extinct fisheries that people are not aware of -- for example, the hudson river sturgeon. people would be amazed to know that there were extensive fisheries for sturgeon

in all rivers of the atlantic coast, and they are gone, and they are not even perceived as lost. if we want to have fish in the future to eat fish to contribute to diversit if we want to have marine habitats that are intact, we must give them at least as much protection as on land we give to land animals and land plants. that is, we have to create large spaces in the sea equivalent to national parks. narrator: preserving large areas of the ocean from fishing will buy time to learn more about how ocean ecosystems work and how their health depends on an intricate balance of many interacting species. in the ocean the recent discovery of the most abundant microscopic photosynthesizer -- prochlorococcus, the base of the ocean food web -- is just one example of how much remains to be discovered.

chisholm: what most people don't realize is that the oceans are responsible for half of the photosynthesis on earth. prochlorococcus is just one of the surprises. we're gonna have many, many, many more -- we do have many discoveries like that every year in science telling us, "oh, boy we really don't understand how this system works." for me it's a constant reminder that we really don't understand these systems. if we continue to play with them and perturb them -- meaning the human impact on the global ecosystem in ways that are stressing the system -- without understanding how it works then i think that any hope for sustainable use of the earth's resources by humans is greatly diminished. and we're only just beginning to understand how the plankton communiti

and the biological production in the ocean affects the carb cycle affects oxygen product affects the nitrogen cycle anall this stuff. and, y know, it's an uncontrolled experiment, and we don't reay know the outcome. and, you know, at that level of ignorance to be messing around with the organisms that are responsible for the regulation and the modulation of the life-support system of humanity is a big risk. and people say "yeah, yeah, yeah, we ought to study it for 20 more years." but i would say that no -- yeah, we should study it for 20 more years, but we ought to get our act together pretty soon because we're playing with fire,

and that is not an exaggeration. narrator: in our experiment -- altering or destroying ecosystems -- are we willing to live without the essential goods and services they provide? not only without the products they provide but their contributions to the regeneration of the human spirit. wilson: humanity needs choices. humanity needs and deserves the choice of visiting natural areas in which the human species evolved and to which we are more akin and spiritually attached than most people realize. if we completely humanize the world, then there's only that choice. if we leave these reserves and include wilderness areas in them where you can enter and see the planet as it was before humanity began to transformt,

then we have a choice. we should not let an irreplaceable resource -- human resource if you want to call it that -- the natural places in the world disappear because once they're gone, they're gone forever. narrator: humanity has reached a point where we affect the earth at the planetary level. the big unknown that influences all earth systems is climate change. linked to human emissions of greenhouse gases like carbon dioxide, global climate change is already changing the earth system. schrag: one often hears environmental scientists talking about tipping points. tipping points are parts of the earth system, when pushed to some threshold, they actually respond in a very abrupt way generally collapsing.

we could be talking about fisheries, where we fish up to a certain point, and then all of a sudden as we fish any more, the population collapses. we could be talking about a tropical forest, where we start cutting it down and everything looks okay, until suddenly we cut one tree and all of a sudden e forest is noger able to sustain itself. or we could be talking about climate change where we add carbon dioxide to the atmosphere and the earth warms and greenland slowly melts until all of a sudden, suddenly, it starts to melt faster and faster and greenland suddenly collapses. these are tipping points. many of them are unknown in the earth system because we don't the details of how everything works well enough to predict exactly where those thresholds are exactly where the tipping points might occur. and yet we know they're there, and we worry that more and more human activities over this next century are gonna lead us to irreversible consequences. there are so many different ways

that humans affect the earth system but climate change has the possibility of being the grand finale, the one overarching environmental change that affects all the other components. holdren: so, you think about what climate change could mean why does it matter? it matters because climate governs the productivity of farms and forests and fisheries. climate governs the prevalence of oppressive heat and humidity and thus the livability of our great cities in the summer. climate governs the geography of disease -- what pathogens and disease vectors can live in what abundance in what places. climate governs the damages that we have to expect from floods and droughts and wildfires and intense tropical storms, hurricanes, and typhoons. climate governs the damage we have to expect from increasing sea level. it governs the distribution and abundance of species --

the organisms we value the organisms we hate. all of that is at risk when you disrupt the climate and we are disrupting the climate. dr. tans: so, i think we're basically endangering our own existence. globally, our influence, or, you could say footprint, on the earth has become so strong that as a result of our economic activities particularly our energy use, we're changing the earth's climate. schrag: the climate problem and the energy problem are so interconnected that they're inseparable. i always talk about the climate-energy challenge because it's really one problem. we have to provide energy for human society to flourish, for economic well-being to continue, and at the same time not add greenhouse gases to our atmosphere that would destroy all those things we want to support. dr. tans: we have to get energy to run our society in such a way that it does not involve emitting carbon dioxide.

that's a tough job because 90% of our energy production now involves emitting carbon dioxide. this will have to be brought down to zero. field: i can't really escape the conclusion that there's nothing more important than getting a handle on fossil-fuel emissions. the difference in impacts between a trajectory in which humanity aggressively looks for alternatives to fossil fuel and a business-as-usual strategy where we aggressively burn all of the resources is just profound in terms of human health transportation, ecosystems economic opportunities. and i guess this is somewhat leaving the science realm, but my sense is that we're really almost out of time in this business and that real leadership could make a difference in both creating economic opportunities and in preventing longerm damages.

schrag: climate change is a huge problem and it's very easy to get pessimistic to think that the problem is so huge, so difficult to solve that we'll actually never be able to do anything about it -- we should just succumb to it and try to adapt as best we can. the truth is that, in fact there's a lot we can do, that humans have a choice. we have technologies available now and more that are around the corner. they can actually supply energy for our society without putting carbon dioxide into the atmosphere. will we stop all climate change? no. climate change is gonna continue for decades to come. but we can minimize its worst impacts, keep the catastrophes from happening. and that's incredibly important, and the irony is it wouldn't even be that expensive. we can replace all of our energy infrastructure rebuild all of our power plants for a small fraction of our total economic well-being. holdren: we keep hearing, "well, we're not gonna change this"

or "we're not gonna change that because it'll hurt the economy." what everybody needs to understand is that not addressing the risks of climate change is likely to have far higher cost to the economy than addressing it. it's much cheaper to take preventive action than to try cope with disaster after it has occurred. and indeed there are many options for addressing climate change that we often call win-win options because we can reduce greenhouse-gas emissions and reduce human influences on climate while getting other benefits while preserving biodiversity, while expanding opportunities for sustainable employment by promoting innovation that develops new products that can deliver the goods and services that people want in climate-friendly ways. there's lots of opportunity out there in the ways that we address the climate issue. this is not something that's all about cost. schrag: fixing climate change doesn't mean doing less. it means doing the same things we do today, just with better technologies, with

smarter technologies. it means driving cars in the future that don't release carbon dioxide into the atmosphere. perhaps they're fuel-cell cars fueled by hydrogen that's produc from wind or solar, or perhaps they're electric cars that are driven from electricity from those sources. what's very clear in the energy system is there's no silver bullet. there's no single solution to all of our problems and yet there's a diversity of approaches out there that together can replace the fossil fuels today that are driving the climate problem. wilson: i've often said that i'm cautiously optimistic and people immediately challenge me and say, "how could you be any kind of optimistic?" and my answer is reading trends and also having some faith in human nature. thompson: all we can do is show what's going on out in the real world

and give the best interpretation of that. and ultimately, i believe that change will come, and it will appear that it happened overnight. what's very exciting right now is that people all over the world are beginning to wake up to the challenge and actually take the responsibility themselves of trying to fix that. i see businesses beginning to take action. i see people small towns, and cities actually beginning to take responsibility for fixing the climate problem. now, they know that individually they can't do very much, and yet they're still committed to working to solve it together. pringle: the only thing you can do is try as an individual to make choices that make sense for biodiversity. and so, we could all give up but i think that would be an awfully sad thing to do. i think we can each individually

fight for what we believe in and i think that's what we should do. thompson: and i think that we can do it on a global basis, internationally, to save a planet a way of life. and to me, i know it's possible, and it's just how do we get all on the same page? schrag: there are many scientists today working on these problems, trying to develop new solutions. but the real solutions and the implementation of those solutions is gonna come from future generations. and we have an incredible responsibility to train those young minds that will ultimately step up and solve these problems in the future.

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funding for this program was provided by... in el salvador a bulldozer accidently strikes the remains of an ancient settlement. and deep below the surface archaeologists open a time capsule 1,400 years old