The Habitable Planet: A Systems Approach to Environmental Science
Biodiversity Decline Interview with William F. Laurance
Interviewer: What is the focus of your research?
BILL: The focus of our research is essentially how do humans affect tropical rain forests. As you probably know, about forty million acres of tropical forest are being destroyed every year. That is about eighty football fields a minute. And as a consequence we are seeing vast landscapes being denuded of forest. We are also seeing the original rain forest being chopped up into isolated islands or parcels. And this might seem like an ironic place to talk about it here because it seems like such a beautiful area. We are in the heart of central Panama and Soberania National Park. But in fact, this is probably the future of much of tropical biology because although it seems like a large area of rain forest, over here we have bulldozers knocking down the forest and over in this direction we have slash and burn farming going on. We have hunters encroaching from all sides of the forest, having major impacts on the wildlife communities. This is an island of forest and it is shrinking over time. There are many different species of plants and animals, in particular, things like jaguars and pumas and harpy eagles that require large areas of space in order to survive. And so really, this is the heart of the question that we are trying to get out here. We want to know are these going to be islands of survival or islands of extinction.
Interviewer: What got you interested in science?
BILL: I was one of those kids that just loved animals and I read books by the British naturalist Gerald Durrell and I got very excited by animals. I started working in zoos in the United States. I eventually, after several summers in zoos, was accepted to work as an intern in Gerald Durrell’s famous zoo in England. And I just loved animals, I raised mountain lions and bear cubs and I was a falconer, I had birds of prey and owls and ferrets and flying squirrels, just a whole menagerie that my long suffering parents put up with. And eventually I just became convinced that zoos were probably not the answer. Although they are a stop gap against the threat of extinction, it is the conservation of habitat, it is the protection of the natural homes, the ecosystems, that is really critical. And so at that time I decided that I really wasn’t going to focus on zoo biology, I wanted to work on conservation of natural ecosystems.
Interviewer: Describe the Biological Dynamics of Forest Fragments Project?
BILL: The Biological Dynamics of Forest Fragments Project is one of the largest ecological experiments in the world. It is a total area of about four hundred square miles in area and inside this study area, in the central Amazon, there has been a whole series of patches of rain forest, fragments of rain forests, that have been isolated from the surrounding areas of forest by slash and burn farming, by cattle pastures. And so you have this hostile surrounding environment and these patches of forest. And of course this is what is happening all through the Amazon; there is an enormous pace of forced destruction occurring in the Amazon. What we are trying to do is to essentially determine which species of monkeys and birds and trees and insects can survive in these small patches, or small islands, and which ones can’t. And of course that is very important for understanding the future of tropical biodiversity.
Interviewer: If you work for the Smithsonian Tropical Research Institute (STRI) in Panama, why is your research not focused here?
BILL: We do some work here in Panama but the Amazon in central America, where we work, is just such a hot spot of forest destruction. And, I mean, if you want to work in forest conservation, it is best to focus on those areas that are sustaining the most dramatic impacts. And so in the Amazon there is incredible forest destruction for cattle ranching; Brazil has gone from having twenty million head of cattle to sixty million head of cattle in just the last fifteen years. There is a huge explosion in soybean farming. There are massive logging operations. There is an avalanche of new highways and roads and other kinds of projects which are creating a lot of problems for the forest. And so, really, we focus on those areas because they are the areas that are really the most important from a conservation perspective.
Interviewer: What originally made you want to come and do research here at STRI?
BILL: Well the Smithsonian Tropical Research Institute is probably the best tropical research institute in the world. So it is a great place to work; scientists here have a lot of freedom, we get to work where we want to work, we are not really told what to do, we are just basically given the tools and allowed to do what we like to do. And for a scientist, for a tropical biologist that is about as close to heaven as it gets.
Interviewer: What are you researching now that will tell us things that we didn’t know already about biodiversity in tropical forests?
BILL: Well we are working on various things. We have our project, our work in the Amazon, on forest fragmentation there. We are doing work in Central Africa on the impacts of roads and logging and hunting. And this turns out to be a very dangerous combination for a lot of wild life in Africa. There is a huge amount of poaching and hunting pressure there. And what is happening is that logging activity has just exploded in Central Africa. And there are now networks, whole labyrinths of roads that are just ramifying all through the forest and so there the Refuge, the places where wildlife used to have to survive, to hide essentially, to be safe from hunting pressure, are disappearing and so the hunters are penetrating now along with the loggers, right into the interiors of the forests. Also we are seeing a lot of slash and burn farmers following virtually in the footsteps of the loggers. And this is happening all through the tropical world, in places as diverse as Borneo, and New Guinea and the Amazon in Central Africa, are essentially having the slash and burn farmers just following right behind the loggers.
Interviewer: Why should people care about tropical forests?
BILL: Well there are lots of reasons to care about tropical forests. Obviously they are the greatest bastions of biological diversity anywhere on the planet, so there are more species of plants and animals here, and of course they are famous for that. Other important reasons: people talk about rain forests being the lungs of the planet and of course they are producing massive amounts of oxygen which help to keep our whole biosphere survivable. 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 we have the greenhouse affect. 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.
Interviewer: How much rainforest has been lost around the globe?
BILL: Over half of the tropical forests have been destroyed now. But it is really variable among different regions. So if you go to the Brazilian Atlantic Forest, for example, you will see that over ninety percent of the forest there has been destroyed. If you go to Madagascar- many of these areas have extremely high richness of species, and very high endemism, that is many species incur uniquely only in those areas. So Madagascar, about ninety five percent of the native forests have been destroyed. In Central America, very large expenses of forest have been destroyed; in the Philippines. You can just go on and on and on. In many areas the levels of forest destruction are far higher than the typical average would be. In Borneo, just in the last few decades, we have seen an island that has been mostly forested and now it has been largely denuded of forest.
Interviewer: Why study habitat fragmentation?
BILL: Habitat fragmentation is the aftermath of forest destruction. And so what we are left with – and almost every time we have a landscape that has been cleared for cattle pastures or for soybeans or for oil pump plantations or whatever reason – are islands, or patches of forest. The most common consequences of forest destruction are these small patches or islands. And, as I mentioned, our national parks are becoming islands, very rapidly. And there are pressures encroaching from the outside continually in most of the parks and reserves. So it is absolutely essential to understand, for the fate of tropical biodiversity, what species are going to be able to persist and which ones are not going to be able to survive in these fragments of forest.
Interviewer: How does destruction of the forest affect rainfall?
BILL: As you can probably hear in the background, we are getting thunder and lightning happening. This is the tropical wet season and so we are going to be getting thunderous rains here, I would say pretty soon. But one of the big concerns is that, in fact, we may be seeing a reduction in rainfall in many tropical areas. The rain forest, it turns out, is very effective at releasing a lot of rainfall that falls on the forest, and goes right back up into the atmosphere. This occurs by a process called evapo-transporation, which means basically that when the trees and plants photosynthesize, they are releasing water vapor up into the atmosphere constantly and so about half of the rainfall that falls on a tropical forest is almost immediately put back up into the atmosphere as water vapor. This helps to maintain continuous cloud cover, and helps to maintain consistent rainfall. And so one of the big concerns, as we are knocking down larger and larger areas of forest, is that the source of water vapor is diminishing and so we may see essentially a desertification process occurring as a consequence of large-scale forest destruction.
Interviewer: Can you clarify the difference between habitat loss and habitat fragmentation.
BILL: Habitat loss is what causes habitat fragmentation. So basically you have got bulldozers or slash and burn farmers or cattle ranchers coming in and they are knocking down areas of forest and in most cases, either by happenstance or design, there are patches of forest that are left over. Sometimes they are just in steep areas where it is difficult to clear or in areas that are difficult to get access to. In other cases they are left aside on purpose for national parks or reserves. And so very often what you have is this island of forest but it is surrounded by a hostile landscape of pastures or slash and burn farming plots or something else like that.
Interviewer: If fragments are only adjacent to an area that has been destroyed, how does fragmentation affect biodiversity?
BILL: Fragmentation in forest edges affect the rainforest in all kinds of ways. The rainforest under its normal conditions is a humid and dark and windless kind of environment. It has been surviving and existing for millions of years and so many, many species have become specialized for these very unique microclimatic conditions and then you juxtapose that with a harsh, dry, windy cattle pasture and the conditions are just completely different. Along the edges of the rainforest fragments we often see that many of the trees die. They either just drop their leaves and die standing — apparently they can’t handle the drought stress — or sometimes they get knocked over, because you get winds building up over the surrounding denuded landscapes and they slam into the forest fragments and they snap trees in half and they topple trees over. The trees are often linked together by vines and so one tree will fall and it will drag other trees down in sort of a domino like fashion. And this just completely changes the ecology of the forest, the microclimate is different, the structure…the architecture of the forest is different and many species of plants and animals simply can’t survive in these degraded conditions.
Interviewer: Can you give an example of how some animals are affected by fragmentation?
BILL: It completely changes the whole ecology of the rainforest, so you have got these very different microclimatic conditions and in effect, what some of Susan Laurance’s work has shown for example is that many species of rainforest birds for example won’t even come close to the edges. Not only will they not cross a road, they won’t even come close to the road. And it is apparently because they have been living in these rain forests, these very dark, special environments for such a long period of time, they are just not accustomed to those very bright, harsh conditions.
Interviewer: How many undiscovered species are in the rainforest?
BILL: One of the really exciting things about working in tropical rain forests is that they are just such a mystery. And there is just so much we don’t know about what is here. Even just in terms of cataloguing the number of species here. I mean, right now we think that there are somewhere between maybe five million and fifty million species living in the tropical rain forests of the world. I mean we are talking about that rough of a reckoning here. One of the reasons that we have such a vague idea of what is here is the rain forest canopy that we can see surrounding us right now. Studies that have been done, for example, in trapping insects up in the canopy have found that in many cases, eighty or ninety percent of the species that they are finding are new to science — completely new to science, never before have they been documented. And if we extrapolate from what we are finding here throughout the tropical world, we are getting numbers like fifty million, which is just an extraordinary number. So really, the rainforest canopy is one of the last great biological frontiers.
Interviewer: If there are so many millions of species, why is it a problem if some are lost?
BILL: There are millions of species but there is also the question of how many millions less do you want to have. There are all kinds of reasons for wanting to conserve tropical bio-diversity: as an indicator – as a canary in the coalmine – for the livability of our entire planet, for their potential pharmaceutical benefits, and other kinds of practical benefits. I mean many people might not care that you have these fantastic drugs originating in rainforests, but if your child happens to have leukemia and it turns out the only treatment for leukemia is the rosy periwinkle which grows only in the rainforest of Madagascar, then, in that case, you might be very happy to have the biological inspiration of a tropical rainforest there to help guide pharmaceutical chemists in order to help them discover new drugs and new compounds.
Interviewer: If there are so many species, how can you possibly find out how many there are and how many are being lost?
BILL: It is an enormous challenge. It really is one of the great challenges, trying to document what is simply out there. And it is tough. It takes muddy-kneed forest biologists to go out there with their binoculars and their nets and their various techniques and just try and count and capture things. And it is a very slow, painstaking process. I think what is perhaps most alarming is that relative to the rate at which the forests are being destroyed, we are really having only a very slow incremental success in terms of documenting the bio-diversity that is there. Clearly, many, many species are disappearing before we ever have a chance to document them, before we ever have a chance to understand them, and before we ever have a chance to assess whether they might have some important benefit for us, for humankind.
Interviewer: Can you describe the process of collecting samples to access the diversity of a forest?
BILL: In the Amazon, we are working a lot with tree communities and it is some of the most biologically rich real estate anywhere on the planet. In a typical hectare of forest, which is about two and a half acres or about two football fields, we get on average about three hundred species of big trees. And then if you multiply that by how many species of insects and vines and epiphytes and birds and reptiles and everything else, I mean the number of species is just stunning. We have teams of field technicians that go out and they actually climb the trees, some of these guys are amazing climbers, and they go up and collect flowers and leaves that we use to help identify the species. It is very difficult, very challenging work. We measure the trees; we study how fast they are dying, which new species of trees are coming into our plots. We have been studying about sixty five thousand individual trees for the last twenty-seven years, and over all that is about thirteen hundred different species of trees within that sample of species. That, just to put it into perspective, just within the plots we are studying in our particular little study area, it is about twice as many species as occur in all of North America.
Interviewer: Why do you need to study the forests for such a long time?
BILL: Our fragmentation study in the Amazon is a long-term study because things take time to change. They don’t instantly disappear. A lot of these trees would normally live between four hundred years and maybe fifteen hundred years. And what perhaps is most stunning is we are seeing such a rapid increase in the death rates of the trees; the mortality rates are just going through the ceiling as a consequence of these edge effects and these environmental changes that we are seeing associated with forest fragmentation. So it is obvious that the ecology of the rainforest is just being altered in such a profound way by forced fragmentation.
Interviewer: How difficult it is to get all the sampling done?
BILL: Studying the trees in the Amazon, is actually a very painstaking process. I mean not only do you have the physical reality of having to get yourself up a hundred, or a hundred and fifty feet high in the canopy in order to get a flower or some leaves in order to identify the tree, you then have to get that down, and you have to press the material, and dry it in a way that people can identify it. And then, because we are dealing with so many different species, in fact no one person or very few people anywhere on the planet would be able to identify all of the species that we are dealing with. And so we work with many specialists from around the world. So we have an individual who may be coming in from botanical gardens in England and he will go through all of our trees in a particular family and he will identify all those particular trees. And so it is a long, painstaking process that involves a lot of people, a lot of effort.
Interviewer: What are the most surprising results from your studies?
BILL: I think what has been most surprising to us is how fast things have changed. I mean we came into this with this perception that a lot of these tropical trees were living a long time, centuries, some of them were living more than a thousand years. And you would think when things survive that long normally, that change would happen pretty slowly. In fact, within just over a quarter of a century, we have seen astounding changes. We have seen huge shifts in the tree communities. Mainly the disturbance adapted pioneer species and the vines which like the forest disturbances are proliferating and we are just generally seeing a decline of what we call old growth species. Many different species of trees are declining in abundance in our study areas.
Interviewer: If there are so many species in tropical forests why are you focusing just on tree species?
BILL: We are focusing on trees, but other people in our group are studying monkeys and birds. I think that one of the really nice things about the Biological Dynamics of Forest Fragments Project is that there is a whole suite of different scientists and different students and researchers working on…all different groups. So, for example, if we are studying a tree species, there is probably somebody else studying the monkey that eats the fruit or somebody else studying the hummingbird that pollinates that tree species. So it is very nice to have information from a whole diverse suite of sources. But when you are dealing with so many species, you really have to specialize on one particular group; it is just not possible to study everything out there in the forest. There is just too much out there.
Interviewer: Why are you so interested in tree species in particular?
BILL: Well the trees are the foundation of the forest. I mean they form the architecture of the forest; they are what determines its microclimate. They are the food sources of most things out there. If you change the tree communities you are really changing the ecology and the habitat for just about everything else.
Interviewer: What are some new research questions you have been working on?
BILL: We are excited because we have got a new grant from the National Science Foundation to continue our studies of tree communities, but now we are also going to look at the smaller trees in the forest. Up to this point we have only been studying trees greater than about four inches in diameter. What this new grant is going to let us do is also go in and measure the smaller trees. And of course, the smaller trees are the things that have come into the forest, that have germinated and recruited into the population since the forests have been fragmented. So we expect to see even more dramatic changes in the small trees. Really they are telling us about the future of the forest.
Interviewer: Most people think of trees in terms of height, why are you measuring the diameter?
BILL: That is just a standard way that we measure them, it is very hard to actually determine how tall a tree is, especially for some of these trees that are two hundred feet tall. So we measure the diameter, that is our index of how fast they are growing and that is our criterion for deciding whether or not we include them with in a study.
Interviewer: Can you estimate how many species are extinct because of habitat fragmentation?
BILL: One would love to be able to put a number on how many species are going extinct because of habitat loss and habitat fragmentation, but when we are talking about a situation where we don’t even know whether we have five million species out here or fifty million species out here, it is extremely difficult to estimate how much is going extinct. We know that there are many, many species disappearing. And many of them have not ever been described scientifically. We know that it is probably a substantial proportion. The numbers that are being thrown around are maybe we might see ultimately the loss of half of all the tropical species, something like that. There is actually quite a lot of debate about the actual numbers. But the bottom line is even the most optimistic scientists don’t doubt the fact that there is going to be an enormous wave of species extinction right now, possibly comparable to the mass extinctions we saw when the dinosaurs disappeared, when the asteroid hit the planet Earth and wiped out huge numbers of species off the planet.
Interviewer: Do you study continuous (unfragmented) forests?
BILL: When we are studying forest fragmentation, we also have to have something to compare it with, a baseline; a control. We have large expanses of intact forest that we use as our control areas. It is sad that in the Amazon, in the central Amazon, many of our areas of intact forest are rapidly vanishing, are rapidly declining. But we still have some areas that we are doing our best to protect. We have had illegal loggers; we have had hunters coming in. Some of the species, like the jaguars and other species that are very sensitive, seem to be declining in abundance, so we are very concerned about that. But these large areas of intact forest are absolutely essential for us because this is what tells us what the original condition was like, what the rainforest was like before it became fragmented.
Interviewer: Do fragmented rain forests lead to other disasters, such as forest fires?
BILL: Yes, often times the fragmentation of the forest is just the beginning of a destructive process. And one of the worst kinds of interactions that we are seeing, one of the most alarming things we are seeing in the Amazon, is an interaction between forest fragmentation and fire. And if you think about it, large intact tracts of rainforest are very difficult to burn. It is very humid and it is very dark — you don’t have much wind there. That kind of system just doesn’t burn, but when you fragment the forest, you end up with these smaller patches of rainforest. Their edges are much drier and you have a lot of dead trees and branches and leaves accumulating along the margins of the fragment. And then you are surrounding them with cattle pastures or with slash and burn farming plots which are these major sources of ignition. The cattle ranchers typically burn their pastures every year. They do that to control weeds and to produce a flusher green grass, which the cattle like. And so, unfortunately, those fires that they light in their pastures burn right to the edge of the rainforest and they very often keep burning right in through the forest. And even though the fires don’t look very impressive, they are just slowly through the rainforest understory. Fire is just not a natural part of the rainforest dynamic; the species and the rainforest are not adapted to surviving those kinds of conditions and so even a little fire burning through the understory will typically kill half of the tree species, all of the vines, it just profoundly alters the ecology of the forest. In fact it makes it more vulnerable to future fires, which will completely destroy the forest.
Interviewer: Describe the difference in vegetation away from the fragment edge and what it looks like actually on a fragment edge?
BILL: If you are in the interior of an intact area of rainforest, you actually are quite surprised as to how open the understory is. It is because you have a continuous canopy overhead, which is capturing most of the light. You oftentimes have very specialized plants growing down in the inner story, which are adapted for living under very low light conditions. It is very dark, it is very humid, and there is almost no wind. Your glasses fog up under there and you go out onto the forest edge and the conditions just dramatically change. Perhaps the first thing you notice when you are getting close to an edge is that it feels like you are walking on corn flakes because suddenly the leaves become very dry and you get dramatic changes in the vegetation structure. The understory just becomes clogged up, overwhelmed by disturbance-adapted and weedy species of plants. The conditions are much hotter, much more variable. Many of the sensitive species of the rainforest interior decline in abundance as you get closer and closer to forest edges. So there is a whole panoply of different kinds of changes that are really happening when you fragment a forest, and when you create these harsh forest edges.
Interviewer: When we drove on the road along the tropical forest, there were lots of vines. Is that a sign of health?
BILL: When you drive along a forest edge, you often see a lot of vines and you might think that is a sign of a healthy forest. In fact, those vines are actually a pretty good indicator of past forest disturbance. They love light, they love disturbance of the rainforest canopy, and they tend to proliferate under those kinds of conditions. So, in fact, we are seeing a lot of roads and forest edges and these things are proliferating and there are some species, whenever you have an environmental change, there are winners and losers and so the vines and the other things that like disturbance are doing great. What we are seeing declining quite dramatically are the old growth rainforest interior specialists. Their geographical ranges are collapsing, they are becoming much less abundant, and they are becoming much more vulnerable to extinction. These are the things that we are really worried about.
Interviewer: Can you discuss the work you do with animals in Africa and explain how it relates to what you do here in Panama?
BILL: In addition to studying forest fragmentation, we are also interested in other kinds of environmental changes and one of the really alarming ones has been the huge proliferation of roads, particularly logging roads in the rainforest in places like central Africa. And there is so much hunting happening as a consequence of these roads. In the past, there would have been refuge, there would have been places where the wildlife could have persisted, areas in deep forest, areas which were inaccessible. Now, unfortunately, because there are just these networks of bulldozer tracks and roads ramifying all through the forest, it is much easier for hunters to get inside there. And so we have a project in central Africa now where we are going out in the daytime and we count monkeys and elephants and bison and bush pigs and forest antelope and all kinds of different animals. And then we also go out at nighttime with spotlights doing the same thing. But we are seeing completely different animals at nighttime. We are seeing tree pangolins and galagos and weird and wonderful beasts that you would just never see anywhere in your life, except for the tropical rainforest at nighttime. And of course we are seeing really dramatic changes. The hunting is affecting the forest in a very important way and so are the roads. The roads are, in some sense, acting as a sort of Pandora’s Box. It is oftentimes the first step in this cascade of uncontrolled activities. In the Amazon, for example, we see roads penetrating into the rainforest; the government is putting in many new roads, and then often times you get slash and burn farmers and cattle ranchers and loggers coming in. When the roads are there you get land speculation, you get a very destructive process with oftentimes leads to just large scale, wholesale forced destruction.
Interviewer: What do you see looking into the future, given the current state of the environment?
BILL: It is a little bit hard to be optimistic when you work in tropical conservation. I mean, we are seeing human populations are still growing rapidly in most developing countries. We are seeing huge increases in industrialization and, of course, there are people in developing nations like India and Brazil and China adopting the same kinds of lifestyles that we have had, that we have enjoyed, so we are seeing a big increase in population, a big increase in consumption. The rates of forest destruction are still very, very high. So I think that we really have our work cut out for us. There have been some successes, there have been some new parks and new reserves that have been designated, but I think we have to be very vigilant. Right now, I feel like we have our fingers in the dike, and we are trying to stave of a potentially catastrophic flood of extinctions. And so I think that is really where we are right now. It is going to take a lot of effort, a lot of dedication, and I think more resources than what we are currently seeing in order to really try and stave off a catastrophic situation in tropical ecosystems.
9.1 Biodiversity Decline Video
Species are being lost at a rapid rate in rainforests and coral reefs. Yet many species still have not been discovered. Tropical scientists struggle to keep ahead of the bulldozers as they work to understand this complex ecosystem. And an ocean biologist predicts the death of life and the "rise of slime" in the sea. How can we protect the biodiversity of these vulnerable ecosystems?
Unit 1 Many Planets, One Earth
Astronomers have discovered dozens of planets orbiting other stars, and space probes have explored many parts of our solar system, but so far scientists have only discovered one place in the universe where conditions are suitable for complex life forms: Earth. In this unit, examine the unique characteristics that make our planet habitable and learn how these conditions were created.
unit 2 Atmosphere
The atmosphere is what makes the Earth habitable. Heat-trapping gases allow ecosystems to flourish. While the NOAA Global Monitoring Project documents the fluctuations in greenhouse gases worldwide, MIT's Kerry Emanuel looks at the role of hurricanes in regulating global climate.
Unit 3 Oceans
Oceans cover three-quarters of the Earth's surface, but many parts of the deep oceans have yet to be explored. Learn about the large-scale ocean circulation patterns that help to regulate temperatures and weather patterns on land, and the microscopic marine organisms that form the base of marine food webs.
Unit 4 Ecosystems
Why are there so many living organisms on Earth, and so many different species? How do the characteristics of the nonliving environment, such as soil quality and water salinity, help determine which organisms thrive in particular areas? These questions are central to the study of ecosystems—communities of living organisms in particular places and the chemical and physical factors that influence them. Learn how scientists study ecosystems to predict how they may change over time and respond to human impacts.
Unit 5 Human Population Dynamics
What factors influence human population growth trends most strongly, and how does population growth or decline impact the environment? Does urbanization threaten our quality of life or offer a pathway to better living conditions? What are the social implications of an aging world population? Discover how demographers approach these questions through the study of human population dynamics.
Unit 6 Risk, Exposure, and Health
We are exposed to numerous chemicals every day from environmental sources such as air and water pollution, pesticides, cleaning products, and food additives. Some of these chemicals are threats to human health, but tracing exposures and determining what levels of risk they pose is a painstaking process. How do harmful substances enter the body, and how do they damage cells? Learn how dangers are assessed, what kind of regulations we use to reduce exposures, and how we manage associated human health risks.
Unit 7 Agriculture
Demographers project that Earth's population will peak during the 21st century at approximately ten billion people. But the amount of new cultivable land that can be brought under production is limited. In many nations, the need to feed a growing population is spurring an intensification of agriculture—finding ways to grow higher yields of food, fuel, and fiber from a given amount of land, water, and labor. This unit describes the physical and environmental factors that limit crop growth and discusses ways of minimizing agriculture's extensive environmental impacts.
unit 8 Water Resources
Earth's water resources, including rivers, lakes, oceans, and underground aquifers, are under stress in many regions. Humans need water for drinking, sanitation, agriculture, and industry; and contaminated water can spread illnesses and disease vectors, so clean water is both an environmental and a public health issue. In this unit, learn how water is distributed around the globe; how it cycles among the oceans, atmosphere, and land; and how human activities are affecting our finite supply of usable water.
unit 9 Biodiversity Decline
Living species on Earth may number anywhere from 5 million to 50 million or more. Although we have yet to identify and describe most of these life forms, we know that many are endangered today by development, pollution, over-harvesting, and other threats. Earth has experienced mass extinctions in the past due to natural causes, but the factors reducing biodiversity today increasingly stem from human activities. In this unit we see how scientists measure biodiversity, how it benefits our species, and what trends might cause Earth's next mass extinction.
unit 10 Energy Challenges
Global energy use increases by the day. Polluting the atmosphere with ever more carbon dioxide is not a viable solution for our future energy needs. Can new technologies such as carbon sequestration and ethanol production help provide the energy we need without pushing the concentrations of CO2 to dangerous levels?
Unit 11 Atmospheric Pollution
Many forms of atmospheric pollution affect human health and the environment at levels from local to global. These contaminants are emitted from diverse sources, and some of them react together to form new compounds in the air. Industrialized nations have made important progress toward controlling some pollutants in recent decades, but air quality is much worse in many developing countries, and global circulation patterns can transport some types of pollution rapidly around the world. In this unit, discover the basic chemistry of atmospheric pollution and learn which human activities have the greatest impacts on air quality.
Unit 12 Earth’s Changing Climate
Earth's climate is a sensitive system that is subject to dramatic shifts over varying time scales. Today human activities are altering the climate system by increasing concentrations of heat-trapping greenhouse gases in the atmosphere, which raises global temperatures. In this unit, examine the science behind global climate change and explore its potential impacts on natural ecosystems and human societies.
Unit 13 Looking Forward: Our Global Experiment
Emerging technologies offer potential solutions to environmental problems. Over the long-term, human ingenuity may ensure the survival not only of our own species but of the complex ecosystems that enhance the quality of human life. In this unit, examine the wide range of efforts now underway to mitigate the worst effects of man-made environmental change, looking toward those that will have a positive impact on the future of our habitable planet.