In a paper* published in the Proceedings of the National Academy of Sciences USA in 2014, Corey Bradshaw and Barry Brook argued that, given the current momentum of human population growth, no demographic “quick fixes” will be enough to change its trajectory in the near future. Therefore, environmental policy will be served better by prioritising measures such as technological and social innovation and reductions in consumption, while treating population reduction as a long-term goal. On his recent visit to Bengaluru, Hari Sridhar spoke to Corey Bradshaw about the genesis of this study and its implications.

Hari Sridhar : You say “our models clearly demonstrate that the current momentum of the global human population precludes any demographic “quick fixes.” If that is the case, what do you suggest should be done
instead?

Corey Bradshaw: I’ll back up a little bit and give you some of the contexts for writing the paper, which will sort of explaining the title and that particular conclusion. Often when I gave public seminars, where I would talk about some environmental problem and future predictions of its worsening, some member of the audience would stand up at the end and say: “Well, the problem is humans. There are just too many of us. So all we need to do is focus on reducing the human population and we will fix all of these other problems. ” That came up so often that I began to think: “Well, how quickly could we fix the overpopulation problem?” Being, among other things, a population dynamics modeller, I decided I could model the human population just as well to look at that question. What would it take, and how long, for the human population to start to decline, either from interventions or catastrophes? Human demographers don’t typically consider catastrophe scenarios when they project human populations. It’s instead done under very strict policy criteria, typically under the expected status quo, with some slight variation in things like family planning and structural change; you know, things like age structure. But we decided to try out more extreme scenarios as well to address that question.

So first we said, “let’s just see what happens when we only adjust fertility.” We did that and the population trajectory was more or less insensitive. Then we said, “let’s see what happens if we impose mass mortality events of various types – a third world war, pandemics, nuclear warfare” – and still the population was fairly resistant, even to these big changes. What we took away from these results was this: yes, population size must be addressed and we should have started looking into this seriously, probably post World War 2 when we were just under two billion people.

We need to address overpopulation, but it’s not going to be something that can be fixed suddenly or be reduced anytime in the next few decades. It’s a century-scale issue. Should we be aiming to reduce the total human population? Yes. Should we be encouraging fertility reduction and family planning? Yes. It’s just that these will have positive outcomes at the century-scale. Now, most of our environmental problems are not things that we can ignore for a century. They have to be dealt with now. So our argument basically was that if we can’t address the human population problem, in the sense of reducing its size quickly, then we need to turn our attention to more immediate fixes, such as addressing consumption and various environmental mitigation policies. That was our main message. But in so doing we managed to anger both sides of the ideological position on the human population debate. In saying that something must be done but it can’t be done quickly, we upset the low-growth proponents. And by saying that we should nevertheless aim for long-term population reduction, we upset the people who are utterly opposed to any sort of fertility reduction or any action on human population growth.

HS: That’s something I want to ask you about – tell us about the attention this paper got within academia and in the media.

CB: Yeah, in the academic setting it was interesting. There were only a few critiques written about the paper and they were fairly weak. As the saying goes “All models are wrong but some are useful”, but what our model said was defensible. I suppose some of the terminology and the interpretation were points of contention with some people, but by and large, the scientific community was satisfied with the result. But in the media, it was completely different. Almost every single journalist I talked to put a particular slant on the results. Because of those two diametrically opposite opinions, people appeared to read anything they wanted to into it. Most people in the media didn’t of course read the paper. They read the title and maybe the abstract and the odd sentence here and there, and took from that whatever their ideological position dictated. There were right-wing media, there were left-wing media, and each had its own bias. I think only a handful of interviewers seemed to grasp the concept, which I didn’t think was that difficult. It also got a lot of responses on these comment streams. I don’t read those most of the time, but there are a lot of crazy people on the internet now. I got all sorts of hate mail, and even indirect death threats. Not serious ones. Just some random person telling me I should be removed from the face of the planet, and things like that. That happens from time to time when you deal with controversial topics.

HS: In the paper, you come up with some figures for what the population will be in 2100, under different scenarios. Could you tell us how much uncertainty there was around these figures?

CB: There was probably much less uncertainty than for most other species that are modelled. Humans tend to census themselves fairly well and we have a reasonable understanding of how many of us there are right now. While demographic data like age-specific survival rates are missing from some parts of the world, generally speaking, at the scale of regions it’s well-known. So in terms of measurement error, the current and even the trends in those demographic rates are robust. Some of the assumptions, such as how much longer we’ll live given future medical innovations, are somewhat uncertain. But as it turns out, we are living so long now that even slight adjustments to longevity don’t make much difference in the long-term to total population size. And even large assumptions about, say, juvenile mortality, don’t make a huge difference, because for a long-lived mammal the most important parameter that modifies population growth generally is the survival of breeding females. And breeding-age women around the world tend to have the highest survival rates, so all the other parameters have smaller effects on population size. So while environmental variability has a large effect on small populations, it has a comparatively small effect on large populations. And we are a very large population. Incorporating a lot of uncertainty didn’t really make much of a difference. But the future scenarios were uncertain – will there be a war, will there be climate change reductions in food availability that will lead to higher juvenile mortality, etc.? We know little about the probability of these things occurring and how important they’ll be.

HS: You say that the momentum is such that we are not going to be able to do much about population growth in the near future, but we could have done something in the past? What do you think we could have done and when?

CB: Well, I will come back to my colleague and friend, Paul Ehrlich and his book “The Population Bomb”, where he was saying in the late 60s and early 70s that we really should have been addressing this issue right after the Second World War when we had the opportunity to keep populations small. But the philosophy or ethic was quite the opposite. The emphasis was on recovery and population and economic growth, fueled by an economic system that depended on a large number of consumers. And the environmental damage wasn’t as obvious as it is today. I think people are still generally of the mindset that we live on an infinite planet and there isn’t any way the human population could change things, like the climate, and kill off entire species. Today, pollution, deforestation and climate change are in everyone’s face, even though some people still prefer to bury their heads in the sand.

But that wasn’t in the psyche of most countries 70 years ago. Some perhaps, like China, clearly had a different view of things, but the Chinese have nearly always had a different view on most things over the course of the last 150 years. And they dealt with it in their own way, controversially of course. And India has had some controversial interventions as well – forced sterilisations and that sort of thing. I think very few countries could put their hands on their hearts and say they haven’t done something wrong in the past with respect to family planning. But Paul was a lone voice in the 1960s in a sea of promotion of growth. Now lots of people argue that Paul Ehrlich was wrong then. But he wasn’t wrong, he was just perhaps a little out of date. He projected what we are going through now, a little bit earlier than it has actually happened. But everything he talked about is coming true. That’s another reason why modelling this stuff mathematically is useful, because it gives you a timeline. It’s approximate, but it tells you whether you need to deal with issues on decadal or century scales.

HS: That brings me to a question I had about this debate of overconsumption versus overpopulation, which is often set up as a developed versus developing world debate. What is your personal take on this?

CB: They are inseparable and can’t be seen as a dichotomy. Several analogies have been used, for example, “two sides of the same coin”. Or the one Paul uses all the time: he says that “arguing whether consumption or population is more important for sustainability is like arguing whether the length or width of a rectangle is more important for calculating its area”. It’s obvious that total damage arising from a population is a product of those two components. If you have a large population with low consumption or a small population with large consumption you have the same result. It’s the same amount of damage, same total consumption. But it is a very sensitive topic; when someone like me, a white fellow from a developed nation, says that the world must reduce its consumption. It seems hypocritical and I would be the first to agree with that. Australians, for example, while only 23 million people have the highest per capita emission rates in the OECD ( Organisation for Economic Co-operation Development). We are one of the highest per capita water users on the planet, even though we live in a desert. We are superlative wasters. Do we need to address that? Absolutely. The possible advantages, I think, many developing nations have is that they have seen the paths that developed nations have gone down: fossil fuel exploitation, reduction of natural resources, and the rising pollution as a result.

In other words, the developing world has very good examples of what not to do, what not to follow. Moreover, the consumption pathway has led to all sorts of corollary issues – obesity, diabetes, heart diseases. Even political stability is not guaranteed. There are plenty of things to avoid. Now I know every country has a set of issues and problems, but I always argue that taking Western societies as examples of what not to do is how developing nations can learn to do better. Because now the technology and knowledge are there, and alternative pathways are now available, which weren’t necessarily the case when Western nations were developing. We didn’t have access to renewable technologies or nuclear power and we didn’t have family planning in mind. So in some ways the developing world is at an advantage and I guess that’s the message I try to get out. Absolutely, I will be the first to scream out that my government isn’t doing enough on the consumption side, just as I will say that to Indians, the Chinese or Africans. In fact, I would also say that my country is probably not doing enough on the population side either.

HS: When you say Australia isn’t doing enough in terms of population, do you mean in controlling immigration? That is something you briefly touch upon in the paper, but which you didn’t include in the regional analysis.

CB: Not in that paper, but I’ve written a subsequent paper about Australia in particular that specifically deals with the immigration issue, which of course is a loaded gun as well; it’s entirely politicized. In Australia, right now, that’s almost the number one election issue: how we deal with refugees in particular, but with migration in general. I myself am an immigrant to Australia: I came from Canada and was naturalised twenty-odd years ago. And there is a certain amount of racism involved there. I happen to be the same colour as most Australians, and so my entry into Australia was probably a little bit easier than someone from say, Sudan or Indonesia. But Australia has a classic European-like demographic structure, in that we don’t really have any intrinsic growth. We are hovering at a slight increase or stability. All of our growth – pretty much all of it (98%) – is from immigration. And that’s a political choice.

We have approximately 2,15,000 net immigrants per year, which is about 1% of the population. So in that paper, we put this in the context of meeting future emission targets. We are already such high emitters, and the addition of more people makes reaching those targets even more difficult. How much more difficult? As it turns out, we have so far to go that even high immigration rates are only going to modify that capacity by 10% or so over the next 50 years. But the other issues are that Australia is a very dry place and has poor soils. The continent has had no glaciation since the Permian, and no major volcanism, so our soils are depleted. We need lots of area to grow food for our own population and we are sustained in a large way by global trade, like many countries these days. One could even argue that we have already exceeded our carrying capacity, so any additional people will put more pressure on our natural systems. We have already lost over 40% of our forest cover in the last 200 years, and the remainder is highly fragmented.

We are losing our world-class coral reef system from agricultural practices and climate change. Overfishing has also been an issue, and we have some of the highest densities of feral animals in the world. We also have the world’s highest mammal extinction rate. People cannot point to Australia as a model for conservation. We have a large protected area network, but even in our largest park, Kakadu, Mammal reductions of up to 95% have happened in the last 35 years. On paper, we might look good, but we’re still having conservation issues like everyone else. Because our lands are marginal and because agricultural development is the primary determinant of deforestation, historically as well as recently, adding more people is just going to put more and more pressure on our natural systems. It will be a case of diminishing returns – every extra person will require food from increasingly marginal resources.

HS: Part of this paper also focuses at the regional level. Could you say a little about what the future scenario for the Indian region looks like?

CB: India is an interesting case. With projected declines in fertility and the rising middle class, the likelihood of increasing much more than doubling, by the end of the century, is low in India. In many parts of Africa, it’s likely to be five to seven times. Therefore, while doubling the number of Indians is definitely something to be concerned about because there are so many already, the main problem is population density; the subcontinent will have the highest population density on the planet by 2100. That’s pretty much non-debatable. What that means for regional political stability, for water availability, for rural politics, etc. is anyone’s guess. Being a population ecologist, one of the truisms I subscribe to is that density feedback happens to every single species and population. The likelihood of conflict is higher, the denser the population. In addition, India is one of the most biodiverse parts of the world. You have the Western Ghats Biodiversity Hotspot next door to Bangalore, for example, which has lots of species but is also highly threatened — this region is probably where we stand to lose a high number of species, maybe second only to Africa. And more than political stability, what concerns me is that all these amazing endemic creatures are going to disappear. Big mammals like the tiger are probably some of the first to drop off the perch, but there are many smaller species that have already been lost and that are in the process of being lost.

HS: I have a couple of questions not specifically about this piece of work. One is about your research interests: correct me if I’m wrong, but it seems like, though you started doing very small-scale, often single-species studies, most of the work you do now is at much larger scales – primarily spatially, but also temporally, i.e., related to long-term datasets. Was that a conscious shift? Do you feel that this kind of research might be more relevant for conservation?

CB: Yes and no. First of all, it’s probably because I get bored easily. I’m a little bit autistic, so I get easily distracted by things. So, I look for different topics and approaches because they interest me more than anything else. On the side of incorporating more than biology into what I do, I think most conservation people who have been in the field for a bit will have the same feeling. I have a bit of a joke about this. I say “Old ecologists never die. They just turn into untrained social scientists”. That’s gotten a bit of a chuckle from many of my friends. When you’ve been around for a while, you realise that the basics of conservation biology have been covered reasonably well. We know that fragmentation is a problem, we know that small populations are a problem, we know that low diversity leads to lower resistance, etc. These basics we established over the last 50 years or so, and now the conservation issues that remain are largely to do with managing human systems-economics, psychology, marketing and the like—that we are not trained in. I’ve tried to delve into that myself. You realise that, as a biologist, you are just sort of fine-tuning our narrative of the devastation. That maybe we can contribute more, I think, societies like the Society for Conservation Biology (SCB) and other national societies are starting to realise. If we want to be relevant, we will have no choice but to incorporate the human component into our work. I think the Society for Conservation Biology is even contemplating a name change because of this phenomenon. There’s also the fact that I enjoy the quantitative side of things. I feel that maths has less nonsense than pretty much any other human endeavour because it’s not ideologically based. One plus one equals two; it’s simple, it’s straightforward. It’s the implications of mathematics that have the politics associated with it. But because I am ‘in the zone, so to speak, when I do my maths, that skill set has allowed me to address questions that are outside of my field with relative ease. Of course, I collaborate with people that are specialists, but that skill has given me the capacity to shift around a bit. That’s something I often say to younger people in the field – if you want to make yourself attractive to employers, supervisors or funding agencies, train yourself to be able to address different problems using mathematics. It’s not the only way of course, but it’s a powerful way.

HS: What first got you interested in ecology and conservation?
CB: That’s a bit of a long story, but I can summarise by saying that it probably began during my childhood in western Canada. I grew up in a small, remote town surrounded by bush and mountains. My father was a fur trapper and hunter, so he took me ‘out bush’ so often that I began to value the very systems we were exploiting for fur and meat. Yes, it was entirely consumptive, but I learned to appreciate functioning ecosystems and the bounty of biodiversity from an early age. My father was also something of a counter-intuitive conservationist in his own way. While a hunter and trapper living off the land, he and his ilk were commonly the most vocal opponents of deforestation by logging companies. When the forests were felled, their livelihoods disappeared. I didn’t know it at the time, but that exposure laid the foundation for my future conservation ethic. But conservation advocacy was never going to be enough for me. The call to science appealed to me greatly and through a fortunate set of circumstances, I was able to complete several degrees and pursue a career in academia. Initially, I was more focused on mainly ecological theory, but I eventually turned to more applied pursuits in the field.

HS: This is my last question –what according to you are the big issues that conservation research has to tackle in the near future?
CB: I think there are several issues that represent ways forward, in not just conservation biology, but in ecology and the interface with many other disciplines. The first one is that moving out of your comfort zone is hard to do. Lots of people avoid this because it takes courage. But moving into a different space, not just working with people in another field, which I call a ‘multi-disciplinary’ approach, but actually engaging in these disciplines yourself; this is true ‘transdisciplinarity’. Moving out of your chosen discipline gives a fresh perspective on things when you cross disciplines with appropriate guidance and the expertise of your collaborators. Often you will discover novel ways to deal with problems. In terms of what to study, I think moving more towards the demonstration of how changing biodiversity affects humans directly. Now a lot of people worry about the monetization of conservation values, for example, the controversy over REDD+ and things like that.

But even demonstrating little things that the average person, who doesn’t necessarily value biodiversity intrinsically, can understand is essential. We’ve done some work on deforestation and flooding events, and the epidemiology of emerging infectious diseases and agricultural practices and how that’s affected by the removal of natural systems. Or looking at wetland dynamics and the production of filtered fresh water, or the frequency of cyclones and other devastating events that kill children and the elderly. Or how much your crop yields will go down if you reduce your pollinators in adjacent forests. Those are things that farmers understand, that the average person on the street understands. No one wants a child to suffer. Putting a service value on everything might sound a little bit contrived sometimes, but I don’t think that we are getting anywhere fast without doing it.

And I also think we need more quantification; we need to quantify these relationships and show them to people. It’s one thing to quantify, but it’s another thing entirely to get the message out. But eventually, even the politicians get the message: this is bad for us, so we shouldn’t do it. But to achieve this uptake, just by publishing your results in a journal and then moving on to the next thing isn’t really going to cut it. We have to be good communicators to a much wider audience. But we are getting better at that; however, as the sea of nonsense in the great Twitter-sphere drowns out all messages, we have to be even more vocal. We have to get into that marketing side of things. And I would promote advocacy. I think scientists can be advocates without sacrificing their objectivity. That said, I don’t think science is the pursuit of objectivity; it’s the pursuit of subjectivity reduction. That’s a topic for another discussion, but a strong argument I have heard many times is that advocating a position based on evidence somehow sacrifices objectivity. I think this view is utter nonsense. We are the people (scientists) who are best informed about these issues, and if we have strong evidence underlying a recommendation we should be vocal about it. Of course, there are associated value systems and ideologies underlying these things, but we shouldn’t just stand back and say we’ve done our job merely by writing about the problems. If that’s all we do, nothing will change for the better.

*Bradshaw CJ & BW Brook. 2014. Human population reduction is not a quick fix for environmental problems. Proceedings of the National Academy of Sciences, 111: 16610-16615.