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The Habitable Planet: A Systems Approach to Environmental Science 

Human Population Dynamics Interview with Deborah Balk

Interviewer: Can you tell us something about what you do.

DEBORAH: I’m a demographer and demographers study human population; some look at the dynamics of human population, others the composition of human population, and, in my particular case, I study aspects of demography – fertility, mortality – things of that nature. Demographers study fertility, mortality, migration, urbanization, and a variety of both descriptive and causal mechanisms that underlie those phenomena. I’m currently looking at urbanization, but I also look at poverty and its relationship to a poverty environment and the relationship to mortality and other aspects of well-being in developing countries. Often when people ask me what demography is I refer to the newspaper; because there is so much demographic content in a newspaper.

I’m trained as a demographer. I have a PhD in Demography. There are a few places in the country where one can get such a degree. Most people who study demography actually train in an allied discipline like Sociology or Economics or occasionally Statistics or Anthropology. I spent some years doing kind of classical demography. And then, in the last eight years or so, I’ve spent quite a bit of time doing spatial demography – integrating demographic data, environmental data, and physical data to examine relationships between people in the environment at a broad scale.

My undergraduate work was in International Relations at the University of Michigan. And there it consisted of mostly a cross between Political Science and Economics. And then I did a Masters in Public Policy. Today’s students who are interested in demographic issues would be well served by some demography programs as well as Sociology and Economics. They are really the leading disciplines in which people get demographic training. I never knew I could become a demographer, let alone a sociologist when I was in high school. I had no idea until I went off to university that these things were possible. In between my masters’ degree and my Ph.D., I did spend some time working in a development context. I lived for two plus years in Bangladesh, and that opened my mind both to policy and its implementation as well as analysis. And that put me back into graduate school. think that often it’s some post-undergraduate experience in a broad sense that leads people to more specialized types of disciplines. Increasingly, demographic training is becoming part of undergraduate curriculum, not so much for degrees, but just in terms of exposure to demographic issues.

A student studying environmental science would be a lot less likely to have some exposure to social science and that’s generally where demography is taught. Though an environmental science student might pay some attention to anthropogenic change as it’s often called in the earth sciences, they would, therefore, learn that humans modify the environment, for example; and that population change and population growth are a cause of environmental outcomes. More and more environmental science programs are offering something called Climate and Society or Environment and Society. Those courses are generally the place where there’s a little bit of exposure to population issues, or least the interaction between humans and their environment. But students who are interested should take some social science classes. Economics is a good framework. Sociology is a good framework. The methods and material of demography are really very valuable input into the study of environmental science.

Interviewer: Can you explain what you mean by a spatial demographer?

DEBORAH: Much of demographic inquiry, demographic transition, is in the study of demographic processes – migration, urbanization, social networks. All these processes are often very spatial intrinsically but we haven’t used the tools of spatial analysis or geography much in demography. Demography has its own set of methods and usually they consist of quite a bit of numeric manipulation and models and quantitative methods, but methods that are not by and large spatial. Spatial information might be brought into those analyses; but looking at a map is not the first or second or perhaps even third thing a demographer would tend to do. As a spatial demographer, what I’ve done is try to be much more explicit in accounting for effects that are typically spatial in nature.

Spatial refers to paradigms that are location and place specific, but which also may refer to a specific location; it may refer to the globe. You know, the earth is a spatial phenomenon. Spatial features that are specific to the earth are often ignored, or omitted or glossed over or generalized in social science in general. So using a spatial framework allows you to look at the relationship between a place and its neighbor or a distance between two entities or flows between those entities or relationships that are clustered in some kind of spatial paradigm or place specific paradigm. It doesn’t mean that things are contiguous necessarily. Trading neighbors may be New York and Los Angeles. I became interested in spatial demography in particular, after spending some time looking at more traditional demographic outcomes – fertility, for example, in part because when we use the standard methods of analysis in quantitative social science, which are multivariate models, we often omit variables that are important, such as community characteristics. The reason we omit them is because the tools we use are survey-driven in part – not entirely, but in this example they’re survey-driven. Having survey analysis be the basis of your conclusions may lead you to omit characteristics that you would not gather from a survey such as environmental characteristics. So understanding whether a household is located in an arid zone versus a tropical zone became increasingly important to me to determine health and mortality outcomes, for example. I realized that the analysis that I was doing would benefit from a more formal consideration of spatial concepts.

When I was in high school, I didn’t know one could study demography. I didn’t even know you could study sociology. I think I knew I could study a bunch of different business options. I could become a lawyer, but it was never evident that I could be a social scientist. I think it was a little clear that I could become a natural scientist, that those were offerings that people actually had careers in – biology or chemistry or physics – but not perhaps as much environmental science and certainly not social science as it relates to environmental science. It took me a good six or seven years of being a demographer ignoring environmental circumstances and environmental conditions and environmental phenomena to realize that I wanted to pay attention to those issues as well. I think in today’s day and age, where environmental concerns are much more present in the schooling of children, that understanding not only environmental science but the role of people as contributors and as recipients of the consequences of environmental change is much more apparent. And hopefully, today’s teachers will be giving a fuller range of options to their students.

Interviewer: Tell me a little about your current research.

DEBORAH: one of the questions I’m paying a lot of attention to is the study of urbanization. Demographers have long considered urbanization and much of understanding demographic trends has been to differentiate between urban and rural residence. My current work on urbanization, though, is to couple what we can understand from an environmental science perspective as well as bringing in the social science and coupling those two together so that we can understand urbanization in a spatial context. We talk about cities as if they’re just a small point on a map as opposed to cities that have a contour that may end at a mountain range or may end at a seacoast. Coastal cities can’t grow the way interior cities can. They have coastlines, so they may be more elongated, for example. They may grow differently because they have different resources available to them or different constraints that inhibit their growth. So my current study of urbanization is an attempt to couple footprints of the cities, which we derive from remote sensing data, with classic and new demographic techniques to measure urbanization estimates and projections of urban change in the future.

The greatest urbanization is going to be in Asia and Africa. That’s where the future growth is going to be largest. The cities of Latin America, Europe, North America and Australia and New Zealand certainly are already fairly well urbanized. They’ll continue to urbanize. But the large share of urban growth that we’ll see in the future will happen in Asia and in Africa. Asia is experiencing a fair amount of economic prosperity and growth at the present time, but Africa is not. Even with growth and economic prosperity, rapid urbanization needs a close look. We don’t currently have very good methods for estimating that urban growth and so some of my research is to refine those methods as well as to bring in a spatial framework, which allows us to look at how cities grow with respect to the land area that they grow on.

Coastal cities occur throughout the world. Some places differ in the coastal orientation of their cities – Australia, for example, has almost all of its cities in a coastal zone; it is a highly coastal country. The lion’s share of the population of Australia lives in a coastal area. Deltaic regions, which means Bangladesh and Calcutta and West Bengal, that whole area of the Ganges Brahmaputra Delta. is a deltaic region with high population density and large cities within those zones. Vietnam is another example where you have large cities well within this deltaic region as well as South China and other parts of China. Africa has a number of landlocked countries as does Asia. Landlocked countries are poorer than countries that have coastal zones. Coastal areas tend to have been very attractive for migration. The development of cities and access to ports and other communications has no doubt been an important part of coastal proximity and coastal location. One recent inquiry is to look at the fraction of the population living in urban areas or rural areas within a low elevation coastal zone that is, we believe, at greater risk of the sea level rise and seaward hazards associated with climate change. We find that the fraction of the population that lives in this low elevation coastal zone, this more vulnerable zone, is not entirely random. In fact, poor countries tend to have greater fractions of their urban areas in this zone than non-poor countries.

During the Indian Ocean tsunami in Indonesia there was this initial press coverage suggesting that the people who lived in Indonesia were poor. And they may be poor in a global sense, but Indonesia is not a terribly poor country, though there are many poor Indonesians – don’t get me wrong. But the area that was affected was a fairly well-off area relative to Indonesia. And relative to the Indian sub-continent that was also affected, the Indonesians in that coastal area were wealthier by and large, had a higher standard of living, lower infant mortality – any number of well-being measures. Did their wealth have something to do with them being at risk from that disaster? Probably not. There are some very interesting long-term questions that some people are starting to look at to say whether or not migration and consumption patterns have altered the environment to may make people more vulnerable to the negative effects of something like a tsunami. But in the instance of this particular tsunami, which was very, very severe, I think even the kinds of protection that nature would normally confer may not have also applied. Those questions, I believe, definitely should be examined as well as whether there is something about being a poor country or poor people in a poor country or poor people in a wealthy country that causes environmental change to occur in particular places which then lead to negative environmental consequences. This is a very important question that people who look at the nexus of earth and social science will be well positioned to answer.

It turns out that the flood zone in the Katrina disaster affected a wealthier area of New Orleans, that more of the area that was flooded was inhabited by people of higher income. However, mortality affected people of lower income. These are preliminary results, but this is where you need a spatial framework to be coupled with a more demographic framework. Without that, we don’t know where the flood zone starts and ends; we don’t know where the mortality starts and ends. And so you need to couple those two pieces together using geography as a meeting ground.

Interviewer: Wasn’t transportation one of the issues in New Orleans?

DEBORAH: Transportation is an important issue. Language is an important issue as well. The Office of Emergency Management in New York City, I believe, has plans that are public transportation oriented. It’s a city of thirteen million, the greater New York area, and should New York need to be evacuated because of impending flood, for example, it would be necessary to move people out with public transportation. It would be necessary to communicate to a large fraction, if not the majority, of the population, including a number of non-native English speakers. The census tells us who speaks English and who doesn’t. And that kind of information should be available in the policy and planning process. You not only need to know how many of those people need to be served, but where they need to be served so that you have the Chinese language directions in the Chinese language areas of New York City; and you have the Spanish language directions for evacuation in the Spanish speaking part of the city. Or you can assume that people are distributed evenly and make sure all directions are available everywhere.

Interviewer: What are the multi-disciplinary or cross-disciplinary uses of your work?

DEBORAH: I think it’s fair to say that what’s one analyst’s input is another analyst’s output. I might be interested in understanding the demographic phenomena. A climate modeler might want to know how many people there are of different ages and the number and the size of the households that they live in. I think this is fairly common across integrated science where you have earth and social science inputs potentially going in both directions. I might be interested in understanding rainfall as it affects family strategies for migration. If farmers in rural Africa knew that there would be a bad rainfall year, they might send some of the family to an urban area to try to find work for a given year. Some of that would have to be analyzed with survey data. You’d have to observe the migration pattern probably through a household survey. But the rainfall data you’re not going to measure through a household survey. You need to measure that through climate measurements. If every household could have a rain station, that would be fantastic.

Demographers have used a variety of methods to study population phenomena. It is analytic models that are largely numeric and data driven. It becomes much easier to do that now that we have more computational capacity with which to do it. It also makes the introduction of spatial phenomenon very explicit if we wish to. Demographers thirty years ago were asking not only questions about the timing and pace of the demographic transition, but evidence for it and the conditions under which it occurred across various cultures and societies. We now have a good understanding of the demographic transition. But many of the theories that were being examined were implicitly spatial. Now we can make them explicitly spatial. We have much more data now. There’s been, in the last roughly forty years, some international consensus both between aid agencies and international institutions on the methods and materials for national censuses. Nowadays most countries try to conduct a decennial census using very similar methods. That means that instead of just doing the basic description, we can dig in deeper and get at some of the more analytic issues. And we can make connections with other characteristics, whether they’re environmental or social in nature, that are also disaggregated that might happen to an individual or within a family or within a community or all of those things happening at once.

Interviewer: Can you tell us about the role that satellite remote sensing plays in your work.

DEBORAH: Satellite remote sensing is a very valuable tool. It’s one that most demographers haven’t used partly because classification of remote sensing data is another discipline in and of itself. You need to be highly specialized. But they’re increasingly coming together. And teams of people are working together. This represents somewhat of a change in the way we work as a scientific community where you have to bring in experts from different disciplines. Most of my projects involve a spatial component involving certainly geographers as well as geophysicists to help with the interpretation of remote sensing images.

Most of the investment in remote sensing has been to look at physical processes, the earth’s physical processes. Urbanization has not been considered one of earth’s physical processes. It’s a human process. So people who have been trying to get missions funded by the remote sensing community are concerned with vegetation change, habitat change, sea surface change, and climate change. By and large, they have not been concerned with urban phenomena. But the urban footprint is easily detectable. What is harder is to classify it in a uniform way from place to place because those places differ in ecological terms.

Future missions could do this better. An open question to the science community is whether or not to put a satellite up there that measures the urban footprint and whether it could measure within urban areas. There is a question as to how well we can use remote sensing imagery to look at informal housing in slums, for example. Slums, even within the social science tools, would fit under the hard to capture populations. In the U.S., we use over-sampling to get at people who are hard to capture in our censuses. Homeless people, for example, are hard to capture. People who live in compromised housing, it would make them hard to capture.

Often when people see a remote sensing image, they say, wow, you can see my house, you know, a high-resolution image. Or, look there are cars. They wonder whether this type of data can be used as a substitute for a population census. In my opinion, it can’t. It can probably tell us something about housing stock. It could tell us, perhaps, something about the wealth of the population in those areas. It’s never going to be a substitute for understanding the breadth of human activity. But coupled with human activity, it can potentially be a very powerful tool. There have been any number of studies in the Amazon region that have taken a close look at migration patterns of individuals and forest cover. There have been other studies that look at urbanization of small towns in the Amazon that use both forest cover from remote sensing imagery and also urban areas through this global rural urban mapping project that I’ve lead for a number of years. But the remote sensing imagery gives them clues to the changes that human beings are making and helps them determine what are the population characteristics both in a causal and consequential way of that change. And so together it’s a very powerful tool. But in and of itself, it’s different pieces of the puzzle.

I’m not suggesting that we want to use one type of data or one method over the other. We want to look at both the tools, remote sensing and remote sensing imagery, as well as the tools of social science and demography, such as multivariate modeling, demographic methods, and models. You’d like to look at both of them at the same time. Household surveys come into that. You want to couple them. But at the same time, there are some questions that are best answered by one or the other. And I wouldn’t dismiss the importance of those contributions as well. Those, in fact, generally feed into the ability to do good into disciplinary work.

Population aging is a good example of a phenomenon that is important to study from a demographic perspective. The demographic methods for understanding aging are really well formulated. And we don’t need remote sensing to tell us about aging. It doesn’t seem to me to have a contribution to understand aging. It’s important to know where people are aging, where the age structure of the population is either very young or very old, and the degree to which we can disaggregate that, all the better. But the power of understanding the implications of aging come from surveys and censuses. I can’t see remote sensing having a contribution to that.

So there are tools and methods and data in a social science. The data come from traditional censuses, which are a type of survey. There are census surveys as well as sample surveys, which are what we, traditionally call surveys. And so those are two of the common tools that we use. We also use clinic records and household registries and vital registration systems as a means for understanding demographic characteristics. So those are standard tools of social science – of the quantitative social sciences that I’m talking about – and demography in particular. Remote sensing on the other hand uses methods of analysis that are intrinsically spatial and computationally intense and which do not necessarily relate to people. They may refer to – the unit of analysis may be a pixel or may be an ecologic unit. But it’s not necessarily associated with an individual or an individual outcome.

Interviewer: Why should we care about the accuracy of a global count?

DEBORAH: There are a lot of reasons to care about an accurate count of human population. At a global scale, we’re collectively and disproportionately contributing to global warming. Most scientists agree that global warming is a certainty. I think all the scientific evidence is in that direction. Of course the subtleties of it are very much debated, but the fact that it’s happening is not. And we know population, the number of people, is one input into that. It’s not just the number of people; it’s what people consume in particular. The footprint of the American population to global warming is, as I understand it, roughly thirty percent, larger than the totality of many other countries combined. Yet China contributes roughly one in six persons to the population of the planet. India similarly, another one in six persons on the planet. India and China are not particularly poor countries. They are developing countries with fast-growing economies. And in the future, more and more residents of those countries are going to want to be following the same consumption patterns. Industries in those countries, to keep their competitive edges globally, are probably going to want to continue using fuel sources that contribute disproportionately to global warming. The incentives or the disincentives for not contributing to those sources are not yet in place. So it’s not just a matter of the total number of population, it’s not only where they are, but also who they are and their income and what that income translates to in terms of consumption.

The reasons that we conduct a census in the U.S. are pretty much the same reason every other country wants to conduct a census. The totality of all those censuses lets us know where the population is, what the distribution of the population is as well as its growth. In the past we continued to revise our estimates of what we believed was true up to the last fifty years, from roughly 1950 to the year 2000. And we continue to revise estimates of future population.

Today’s global population is roughly six billion persons. In the year 2050 we expect the population to be a little bit more than nine billion globally. But these estimates have a fair degree of uncertainty in them. If we look at the low variant we’d estimate somewhere in the seven and a half billion persons. And the high variant would be more like ten and a half billion persons. Interestingly, if today’s demographic rates, rates of fertility and mortality, persist as they are currently, we would have a population of roughly eleven and a half billion in 2050. This means that we’re assuming some changes are coming ahead. Demographic methods help us determine what those changes are because they require that we look at the age distribution of population. We know, for example, that women over the age of fifty tend to have no children biologically and that girls under the age of fifteen don’t. So we have estimates about fertility, age-specific fertility. Marriage, age of marriage, for example, is another component that demographers pay some attention to. We also look at changes in mortality and also changes in life expectancy that result from mortality changes. But those bounds of uncertainty should be known at the same time that we talk about the nine billion number. And I suspect that for the climate community, for example, it would make a difference if there is an extra billion here or there. And it may matter where those billion are – If there’s an extra billion Americans with high consumption of global warming pollutants, for example, or if they are primarily Africans who don’t consume to the same degree. On the other hand, there may be other environmental consequences if they don’t share the contributions to global warming pollution.

Interviewer: Can you define “urban”?

DEBORAH: What’s urban? That’s a really good question. I don’t actually have an answer; and I study urbanization. I would consider any settlement with recognizable urban properties in the looser sense to be urban. But every country describes what’s urban somewhat differently. Many, many countries have official definitions, for example, from communities involved in non-agricultural activities or have up to seventy-five percent of the population engaged in non-agricultural activities in a contiguous fashion that is apart from such and such. Some countries have population density thresholds to establish what’s urban. Others have population numbers – ten thousand persons or more, twenty thousand persons or more, fifty thousand persons or more. I care more about settlements. I also think from an environmental perspective it is important to pay attention to density in and of itself. Environmental conditions are not the only thing, though, for which density matters. Service delivery is another really good reason. The delivery of hospital services, schools – these service delivery aspects of delivering health and educational services has a very direct feed back into understanding demographic behavior.

We know, for example, that as societies become more educated and people become more educated, they tend to have lower fertility. So a good investment from a demographic perspective, if a country might have an objective in lowering its fertility, would be to supply education. Of course, there are a lots of good reasons to have strong educational programs in and of themselves, and similarly for health. In pre-transitional societies, couples would have lots and lots of children because they did not know which children would live and die nor were there the means to regulate fertility effectively. In the present day there are effective means of fertility regulation as well as anti-natal, pre-natal, and infant care, so the chances of having infants survive is much greater. So often what we see is that fertility decline and mortality decline do not occur at the same pace. And in some countries where mortality falls sooner than fertility does, we see higher growth rates or a delayed demographic transition.

Interviewer: What role does government play in demographics?

DEBORAH: National and provincial governments often have both proactive and restrictive ways of influencing demographic change. Perhaps the best know example is the one child policy in China, which has more recently been relaxed for rural areas. Under that system, we see a somewhat unusual age structure in China but we also see the effects of fertility decline very rapidly. Conversely you have policies in many European countries that have experienced fertility decline. These policies aren’t one-child policies; but two- or three- child policies where some countries have incentives for additional children Tax rebates, for example, are incentives for working women so that they have a full year maternity leave, or for families so that there’s the ability for paternity leave. These are all the types of policies that governments might implement on the proactive side to alter demographic behavior. Similarly there are restrictive policies – the lack of abortion rights in some countries leads to high numbers of orphans in some countries. And just simple mortality outcome. AIDS has led to a much higher occurrence of orphanage in Africa and families that consist of grandparents and grandchildren without any middle generation.

Interviewer: is the census the same in every country?

DEBORAH: All censuses aren’t the same. First of all, every country does not have a decennial census. Most do. Some have an estimate. Censuses do not collect the same variables from one census to another. A good example – in the United States, the census has a question on race and ethnicity. Information on race and ethnicity has been collected until the 2000 census differently from the way it was collected in the 2000 census. In the United States, it’s an important part of understanding the social fabric of society to know one’s race and ethnicity and also because social services are delivered based on census data. So knowing where people with different needs are is an important component of delivering services. In France, no one is asked race or ethnicity. It’s believed to be racist to ask that question. And the international community has not engaged so much in a dialogue on is it or is it not racist.

In some of the wealthier countries of the world, particularly in Scandinavia, they’re moving away from census taking to vital registration systems. Because they understand the importance of this decennial snapshot, they make their vital registration information comply with a set of standard outputs that look like census outputs, but they, if fact, come from a registration system.Those registration systems would be much harder probably to implement in a place like Africa than they are in smaller Scandinavian countries where there is not only a high degree of education, but there’s also a fair degree of cultural homogenization. In censuses, there is a relationship between the effectiveness of a census and the amount of trust. If it’s believed that the information you’re giving to your census taker is going to be used against your interests, you would be a whole lot less likely to supply it.

But even though estimating population counts is uniform, it is the easiest of all information to collect from every census. If one country supplies data in very small census sub units, they could easily be processed into, say, a quadrilateral grid, a grid unit that earth and environmental sciences tend to use, for example, in climate modeling. Climate models tend to be large in matter of degrees, one degree, half degree – things of that nature. But there are other phenomena that you would want to study at a much finer resolution. In an urban area you would not want to look at a one degree grid; you would rather look at a thirty meter grid. So if you were studying urban phenomena, you would want a much higher resolution database and therefore, you would want census units that are very finely resolved.

Interviewer: How many people have lived on the earth in the past compared to now?

DEBORAH: Though population growth in the last hundred years, and particularly in the last fifty years, has been unprecedented, especially in terms of the number of people we add to the planet each day, the cumulative population of people who have lived in history does far exceed the current population size. I am not by any means trying to dismiss the importance of having a population of six billion on the earth. That is a significant number. But we often see the relationship between population and the environment or resources being made as if it’s a small square and on one axis you have population and on the other axis you have time. And there is no little blip to account for the fact that it really should be a very long rectangle.

When we look at population growth over time we often look at only 1950 to the present or we look at 1850 to the present. When we look at 1850 to the present, we see a very lowlying curve until around 1950. And then we see it starting to rise, and then we see it take off – sky rocket – an exponential curve classic. That growth is unprecedented. It’s important to recognize the phenomenon that let that curve happen, to take off in a small period of time. But it’s also important to have some perspective and to draw out from what would be a fairly square box, a square graph from 1950 to the present looking at human population growth. Go back in time, you know, to our best guess estimates to 1850, or 1750, or 1650 or even the year 1000 or pre-BC, and you would see the same relatively very low, sloping curve over time. And if you flipped it around, you would see that the total population in the past cumulative to today is, in fact, greater than today’s population. Is that important? It’s not important from the policy perspective of needing to deal with today’s population issues. But it’s relevant from understanding the resource population environment. Forests don’t grow overnight; but in this one instance it seems like people did.

In the past, population growth was limited in large part due to disease. We had a very poor knowledge of disease transmission in the past. It’s interesting that in the past the death rates associated with urban areas were higher than in rural areas. Urban areas had certain conditions that were very unfavorable. Very poor sewerage, very poor water and also more crowding, and certain diseases are the result of crowding and airborne transmission. Those kinds of things were much more common in the past. We can ask will they become more common in the future once again as we live in more crowded cities; because we will.

Interviewer: What is the “carrying capacity” of the earth? How many people can the earth support?

DEBORAH: You know, that’s a good question. To my thinking it’s a theoretical question. There has been a long demographic debate, the arguments of which sometimes conflict, sometimes converge. There are two schools of thought on population growth. One is that population growth will far outweigh resources. That belief is commonly associated with the work of Malthus from the late 1700’s. The other school of thought is commonly associated with Ester Boserup, which is that technology shifts with population. So you have one level of population pushing out the technological innovations at any given time. So more population can create and sustain new technologies, which allow for greater populations to be sustained. These two views have established some form of conflict in population science. Environmental scientists have often adapted the Malthusian view, perhaps without sufficient rigor. It would be a very valuable thing for people looking at ecological and environmental change to look at both perspectives. But it’s an open question as to how many people the planet can support. One is taking the planet as a totality; not as a particular ecosystem on the planet, for example. One might be a particularly poor or a particularly wealthy country on the planet. But as a totality, the “carrying capacity” of the planet is an open question. I think that it very much depends on action – it depends on action in the present, policy in the present, and behavior in the present at the individual, the community, and the national and international level. This is where the question of environmental population interactions becomes really obvious. The climate change conditions, for example. Simple policies put in place now would probably avert some aspects of global warming. Which policies are they? Are they reduced fertility or are they carbon emissions reduction programs? Or are they both? These are open questions but they require sufficient scientific inquiry from an interdisciplinary perspective.

After some years of working with environmental scientists, I was impressed with the assumption that I found many people making that population was a prime cause of environmental problems without a careful look at population phenomena. Population growth, especially when that growth is rapid, tends to be problematic. Societies, communities can’t plan very well for rapid growth. So I understand where that concern comes from. But we now have the methods and materials for understanding growth. And I think most demographers don’t treat population growth in and of itself as problematic. They want to deconstruct it and determine which aspects of it are more vulnerable or likely to be more problematic than others, or what are the implications of different types of growth? It’s in that context that you can pinpoint where and why particular environmental concerns may arise. But I’m not comfortable assuming that population is the main cause of most environmental circumstances. And I would encourage future environmental scientists to not just look at the demography but also the broad social and economic or political determinants that couple those demographic processes.

There are three hundred million Americans. Yet, as a nation, we contribute much more to our fair shareoft global warming pollutants. We probably also contribute to other kinds of environmental change disproportionately. I think it’s incumbent on the U.S. as individuals and as a national entity to be a leader in the global community. We can set standards; we can have high innovation. We can implement policies and set by example. You know, it would be in my thinking very unfair for the United States to start pointing figures at India and China which each have a billion persons in them and to say, well you have to rely on public transportation – you’re contributing too much to the global pollutant mass. You come up with good public transportation systems. We’re going still drive around in our SUVs. I think that would be a huge double standard. But that’s basically the equivalent of what we have now. And I think it’s time for the U.S. to take a close look at those things.

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