13 Oct 2011

Revisiting Population Growth: The Impact of Ecological Limits

Demographers are predicting that world population will climb to 10 billion later this century. But with the planet heating up and growing numbers of people putting increasing pressure on water and food supplies and on life-sustaining ecosystems, will this projected population boom turn into a bust?
By robert engelman

The hard part about predicting the future, someone once said, is that it hasn’t happened yet. So it’s a bit curious that so few experts question the received demographic wisdom that the Earth will be home to roughly 9 billion people in 2050 and a stable 10 billion at the century’s end. Demographers seem comfortable projecting that life expectancy will keep rising while birth rates drift steadily downward, until human numbers hold steady with 3 billion more people than are alive today.

What’s odd about this demographic forecast is how little it seems to square with environmental ones. There’s little scientific dispute that the world is heading toward a warmer and harsher climate, less dependable water and energy supplies, less intact ecosystems with fewer species, more acidic oceans, and less naturally productive soils. Are we so smart and inventive that not one of these trends will have any impact on the number of human beings the planet sustains? When you put demographic projections side by side with environmental ones, the former actually mock the latter, suggesting that nothing in store for us will be more than an irritant. Human life will be less pleasant, perhaps, but it will never actually be threatened.

Some analysts, ranging from scientists David Pimentel of Cornell University to financial advisor and philanthropist Jeremy Grantham, dare to underline the possibility of a darker alternative future. Defying the
Some forecast that apocalyptic horsemen old and new could cause widespread death as the environment unravels.
optimistic majority, they suggest that humanity long ago overshot a truly sustainable world population, implying that apocalyptic horsemen old and new could cause widespread death as the environment unravels. Most writers on environment and population are loathe to touch such predictions. But we should be asking, at least, whether such possibilities are real enough to temper the usual demographic confidence about future population projections.

For now, we can indeed be highly confident that world population will top 7 billion by the end of this year. We’re close to that number already and currently adding about 216,000 people per day. But the United Nations “medium variant” population projection, the gold standard for expert expectation of the demographic future, takes a long leap of faith: It assumes no demographic influence from the coming environmental changes that could leave us living on what NASA climatologist James Hansen has dubbed “a different planet.”

How different? Significantly warmer, according to the 2007 assessment of the Intergovernmental Panel on Climate Change — as much as 10 degrees Fahrenheit more than today on average. Sea levels from two to six feet higher than today’s — vertically, meaning that seawater could move hundreds of feet inland over currently inhabited coastal land. Greater extremes of both severe droughts and intense storms. Shifting patterns of infectious disease as new landscapes open for pathogen survival and spread. Disruptions of global ecosystems as rising temperatures and shifting precipitation patterns buffet and scatter animal and plant species. The eventual melting of Himalayan glaciers, upsetting supplies of fresh water on which 1.3 billion South Asians and Chinese (and, of course, that number is rising) depend for food production.

And that’s just climate change, based on the more dramatic end of the range the IPCC and other scientific groups project. Yet even if we leave aside the likelihood of a less accommodating climate, population growth itself undermines the basis for its own continuation in other ways. Since
Population growth itself undermines the basis for its own continuation.
1900, countries home to nearly half the world’s people have moved into conditions of chronic water stress or scarcity based on falling per-capita supply of renewable fresh water. Levels of aquifers and even many lakes around the world are falling as a result. In a mere 14 years, based on median population projections, most of North Africa and the Middle East, plus Pakistan, South Africa and large parts of China and India, will be driven by water scarcity to increasing dependence on food imports “even at high levels of irrigation efficiency,” according to the International Water Management Institute.

The world’s net land under cultivation has scarcely expanded since 1960, with millions of acres of farmland gobbled by urban development while roughly equal amounts of less fertile land come under the plow. The doubling of humanity has cut the amount of cropland per person in half. And much of this essential asset is declining in quality as constant production saps nutrients that are critical to human health, while the soil itself erodes through the double whammy of rough weather and less-than-perfect human care. Fertilizer helps restore fertility (though rarely micronutrients), but at ever-higher prices and through massive inputs of non-renewable resources such as oil, natural gas, and key minerals. Phosphorus in particular is a non-renewable mineral essential to all life, yet it is being depleted and wasted at increasingly rapid rates, leading to fears of imminent “peak phosphorus.”

We can recycle phosphorus, potassium, nitrogen, and other essential minerals and nutrients, but the number of people that even the most efficient recycling could support may be much less than today’s world population. In 1997, Canadian geographer Vaclav Smil calculated that were it not for the industrial fixation of nitrogen, the world’s population would probably not have exceeded 4 billion people — 3 billion fewer than are alive today. It’s likely that organic agriculture can feed many more people than it does currently, but the hard accounting of the nutrients in today’s 7 billion human bodies, let alone tomorrow’s projected 10 billion, challenges the hope that a climate-neutral agriculture system could feed us all.

Food production also requires many services of nature that conventional agronomy tends to ignore in projecting future food supplies, and the dependability of these services appears to be fraying. Roughly one out of every two or three forkfuls of food relies on natural pollination, yet many of the world’s most important pollinators are in trouble. Honeybees are
As population growth sends human beings into once-isolated ecosystems, new disease vectors thrive.
succumbing to the tiny varroa mite, while vast numbers of bird species face threats ranging from habitat loss to housecats. Bats and countless other pest-eaters are falling prey to environmental insults scientists don’t yet fully understand. And the loss of plant and animal biodiversity generally makes humanity ever-more dependent on a handful of key crop species and chemical inputs that make food production less, rather than more, resilient. One needn’t argue that the rising grain prices, food riots, and famine parts of the world have experienced in the past few years are purely an outcome of population growth to worry that at some point further growth will be limited by constrained food supplies.

As population growth sends human beings into ecosystems that were once isolated, new disease vectors encounter the attraction of large packages of protoplasm that walk on two legs and can move anywhere on the planet within hours. In the last half-century, dozens of new infectious diseases have emerged. The most notable, HIV/AIDS, has led to some 25 million excess deaths, a megacity-sized number even in a world population of billions. In Lesotho, the pandemic pushed the death rate from 10 deaths per thousand people per year in the early 1990s to 18 per thousand a decade later. In South Africa the combination of falling fertility and HIV-related deaths has pressed down the population growth rate to 0.5 percent annually, half the rate of the United States. As the world’s climate warms, the areas affected by such diseases will likely shift in unpredictable ways, with malarial and dengue-carrying mosquitoes moving into temporal zones while warming waters contribute to cholera outbreaks in areas once immune.

To be fair, the demographers who craft population projections are not actively judging that birth, death, and migration rates are immune to the effects of environmental change and natural resource scarcity. Rather they argue, reasonably enough, that there is no scientifically rigorous way to weigh the likelihood of such demographic impacts. So it makes more sense to simply extend current trend lines in population change — rising life expectancy, falling fertility, higher proportions of people living in urban areas. These trends are then extrapolated into an assumedly surprise-free future. The well-known investor caveat that past performance is no guarantee of future results goes unstated in the conventional demographic forecast.

Is such a surprise-free future likely? That’s a subjective question each of us must answer based on our own experience and hunches. Next to no research has assessed the likely impacts of human-caused climate change,
Agronomists have lost some of their confidence that food production will keep pace with rising populations.
ecosystem disruption, or energy and resource scarcity on the two main determinants of demographic change: births and deaths. Migration related to climate change is a more common subject for research, with projections ranging from 50 million to 1 billion people displaced by environmental factors — including climate change — by 2050. The mainstream projections cluster around 200 million, but no one argues that there is a compelling scientific argument for any of these numbers.

The IPCC and other climate-change authorities have noted that extremely hot weather can kill, with the elderly, immune-compromised, low-income, or socially isolated among the most vulnerable. An estimated 35,000 people died during the European heat wave of 2003. The U.S. Centers for Disease Control and Prevention cites research projecting that heat-related deaths could multiply as much as seven-fold by the century’s end.

In the past few years, agronomists have lost some of their earlier confidence that food production, even with genetically modified crops, will keep pace with rising global populations in a changing climate. Already, weather-related disasters, from blistering heat waves to flooded farm fields, have contributed to widening gaps between food production and global consumption. The resulting price increases — stoked also by biofuels production encouraged in part to slow climate change — have led to food riots that cost lives and helped topple governments from the Middle East to Haiti.

If this is what we see a decade into the new century, what will unfold in the next 90 years? “What a horrible world it will be if food really becomes short from one year to the next,” wheat physiologist Matthew Reynolds told The New York Times in June. “What will that do to society?” What, more specifically, will it do to life expectancy, fertility, and migration? Fundamentally, these questions are unanswerable from the vantage point of the present, and there’s a lesson in this. We shouldn’t be so confident that the demographers can expertly forecast what the world’s population will look like beyond the next few years. A few demographers are willing to acknowledge this themselves.


The World at 7 Billion:
Can We Stop Growing Now?

The World at 7 Billion: Can We Stop Growing Now?
With the global impact of population growth becoming more and more evident, Robert Engelman writes that a two-pronged response is imperative: empower women to make their own decisions on childbearing and rein in our excessive consumption of resources.
“Continuing world population growth through mid-century seems nearly certain,” University of California, Berkeley, demographer Ronald Lee noted recently in Science. “But nearly all population forecasts... implicitly assume that population growth will occur in a neutral zone without negative economic or environmental feedback. [Whether this occurs] will depend in part on the success of policy measures to reduce the environmental impact of economic and demographic growth.”

It’s certainly possible that ingenuity, resilience and effective governance will manage the stresses humanity faces in the decades ahead and will keep life expectancy growing in spite of them. Slashing per-capita energy and resource consumption would certainly help. A sustainable population size, it’s worth adding, will be easier to maintain if societies also assure women the autonomy and contraceptive means they need to avoid unwanted pregnancies. For anyone paying attention to the science of climate change and the realities of a rapidly changing global environment, however, it seems foolish to treat projections of 10 billion people at the end of this century as respectfully as a prediction of a solar eclipse or the appearance of a well-studied comet. A bit more humility about population’s path in an uncertain and dangerous century would be more consistent with the fact that the future, like a comet astronomers have never spotted, has not yet arrived.


Robert Engelman is president of the Worldwatch Institute, an environmental research organization based in Washington, D.C. The Population Institute awarded his book, More: Population, Nature, and What Women Want, the Global Media Award for Individual Reporting in 2008. A former newspaper reporter who covered science and politics, Engelman previously wrote for Yale e360 on the environmental impact of soaring populations and growing consumption.

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Because the population of the world ultimately affects most of the issues that we all really care about, the 7 Billion: It's Time to Talk campaign ( is working to open up the conversation on population to new audiences around the globe. When everyone recognizes that there is a need to talk openly about population growth and the importance of family planning, the empowerment of women, and reproductive health and rights, we can more easily find the solutions to issues like global hunger and the environment. When people discover how a rapidly growing world population affects them and their hopes for the future, we know that more people, particularly young adults, will want to lend their voices to the global discussion.

Posted by Joseph J Bish on 13 Oct 2011

Even more determining for our planet's environment than population growth is the growth of consumption. According to this, we already surpassed the earth's carrying capacity and are currently using one and a half planets worth of resources (, which means that we are consuming the resources of our descendants - definitely not a sustainable way to go! With everyone and their mother wanting to live "the american dream" all over the world, we urgently need not only to curb down population, but finding and implementing a truly ecological development model that includes sustainable consumption - a most challenging task, indeed!

Posted by tom on 13 Oct 2011

Each time there is a debate on this point, people oppose demography and consumption. It is always the same, looking as if people could only repeat the same patterns for ages.

In short (at least in europe), if you are "left wing", demography is not an issue, consumption is (as previous comment suggests). This is the old anti malthusian approach voiced by the fathers of radical leftism (bakunin, Marx etc). Moreover consumption has a moral dimension, which lacks in the demographic approach: it is obvious to see what is wrong in appropriation of goods and lands, but difficult to condemn a poor peasant because he does what human have been doing for so long: having many kids.

It is quite clear that,on the other political side, some people lazily blame demography to advocate the sustainability of their huge personal consumption (if we were less we could all consume so much...), forgeting that they are themselves the products of a tremendous european demographic wave that offseted native indian by force, after having overcrowded europe.

But the current politically correct left approach is quite peculiar if we think about history. Of course Marx made fun of Malthus (Marx himself had a large family living in poverty...), but after him some progressist, who called themselves neo malthusian, fought the influence of the church and the conservatives to advocate a decrease in the number of child among poor families. They were severly fought by authorities in a pre world war context: nationalism needed many soldier and the number was the real force. After the two wars, this political current fade out and strangely enough the large family values were adopted by the state, whether run by "left" or "right".

There is one idea of Malthus (a conservative) that is still valid in many contexts and is overlooked. It is that human tend to have as many child as the current level of food production can barely sustain. Off course there is a part that is unequally distributed and kept by only a few (the western world), but whatever the rest amounts to, the global population will grow to fill the gap, untill the death toll is too large so that people cannot find the force to have more kids. This has as consequence, which grounded the neo malthusianist approach, that this excess of mouth, which cannot be fed on site, will enlarge the urban Lumpen proletariat and be used to fuel even more unequality by putting pressure on the workforce.

For some people this approach is wrong. This is the case, among many other, of the swedish statistician Hans Rosling. They point rightly at the fact that in complex modern societies people do not follow the malthusian pattern anylonger. This is clearly the case in Germany. In a complex modern society, food is not the limiting factor, but complexity itself. Traditional patterns of life have been smashed and it becomes harder to plan a relationship, ie, to form a couple (studies, stress, mobility), then to have sexual intercourse (leisure time is no free time, TV is there), and we have condoms to postpone a birth that is seen as a problem rather than a necessity for our old days (school, care, transportation etc...).

But, this complex social pattern that has commanded the demographic evolution of last century in the west and parts of Asia is not necessarily the one that will apply to other countries or even to the west in the future and there it is as reasonable to think that complexity will not be materially sustainable and expandable so that Malthus will continue to be right. This is all the more scary if we think that this time the productivity might go in the other direction.

So, all this post to answer the comment of Tom. Demography and consumption are linked as well as poverty and demography were thought to be linked. The demographic pressure will not only fuel inequalities, like conservative and progressist Malthusian thought, but may force the productive system toward a more intensive, heavy consumming one. To sustain the number, production means might become more and more unstainable, and may be exponentially so.

Today the population that is growing is urban, not rural, and this does not seem at all sustainable to me. This people will be forced into a heavy consumption pattern of fueled transportation and heating, industrially produced food and high output industrial jobs, just to survive.

Posted by Kervennic on 13 Oct 2011

I am an environmentalist working in Mozambique, undertaking evaluations on climate varability and change, community natural resource use, existing and perceived stresses. This article is very pertinent for the north of Mozambique where there are already stresses on water resources, fisheries are collapsing, existing diseases are worsening such as brown steaking disease in cassava, new diseases are coming in. Climate variability is increasing teh existing stresses, with communities noting that variable summer rainfall is worsening fisheries catches. Hotter summers are reducing crop production. Lack of cold front arriving from the south bringing light winter rainfall is reducing cassava production. People are complaining of hunger even though the harvest has just been completed.

For these communities, conflicts over water and food resources are already occurring at community level. There are indications of local and provincila migration already occurring. In all likelihood the populations in these areas will decline, as there are no adaptive measures sufficient to cope with existing livelihoods problems, never mind those from over use of resources and climate variability and change. It is a bleak future.

Posted by Michaela Cosijn on 14 Oct 2011

Thank you for bringing up this most urgent issue in a forthright way. As I look at the facts coldly, there appears no alternative to massive collapse. People say that technology will solve this problem, but didn't technology get us into this mess?

Sometimes I feel like an amoeba in a petri dish, and all the other little amoebi are shouting "let's grow, growth is good"; and I'm sitting there helpless knowing what lies ahead.

Posted by John Dyer on 14 Oct 2011

An excellent article making some valid and interesting points, but I wonder whether it addresses the right question.

Much of the population debate centers around the question: 'How large a population can the earth support?' It's an important question (obviously), but it seems to suggest that preventing population growth from exceeding that limit is the only important consideration; that preventing disaster contitutes success.

Surely part of the equation ought to be the effect of human population on the rest of the planet. I don't know if we can feed 10 billion people, but if the price of doing so is to turn the whole planet into a life support system for humanity, then as far as I am concerned we should be making every effort to ensure that we never have to.

Posted by John McConnaughy on 15 Oct 2011

There has been no discussion of the importance of energy supply (and demand) in this article and its threads. Perhaps, this is less an oversight, than that it is subsumed in the question of consumption. But with always sufficient supplies of useful energy, much can be accomplished to alleviate such issues as food production and water consumption, so that if there is indeed a "tipping point" in energy as the world population expands, the probablilty of sufficient energy production becomes crucial. Much more could be said on this topic.

Posted by Morton Brussel on 17 Oct 2011

Thank you for this very interesting article - nothing more welcome for someone who is now and then working with projections and forward looking tools. I liked equally much the insightful comments posted by readers (in particular Kervenic's discussion about inter-linkages that show that population dynamics IS a 'continuum', & John McConnaughy sharp point in case).

Posted by MT on 18 Oct 2011

The other leg of the stool on which our societies rest is an economy firmly based on economic growth. Economic growth comes from two main sources: growth in the work force (i.e. overall population) and increased productivity per worker. Of the two, the majority of economic growth comes from increases in the work force.

What then comes of a society that, whether by choice or through force of nature, declines in numbers? We have seen in these past years the impact on our global society of a short disruption in that pattern of growth, yet a genuine decline in global population would make our 'great recession' look like the good old days. In addition to the challenges posed by the authors, we must also deal with how to transition to a sustainable, rather than growth-based, economy.

I'm not sure we're any more able to achieve that than we are to overcome the physical constraints limiting our global agricultural system.

Posted by Rob on 19 Oct 2011

Thanks for your good job in attempt to save our planet earth from being exticnt environmentally. I would wish to understand clearly how population growth and poverty in developing countries has led to water pollution. Thanks in advance.

Posted by MUTAI HILLARY on 21 Oct 2011

What an interesting article! Took into consideration so many aspects of the problem, but never touched the main issue - the human nature. No matter what projections are, humans will never be able to control themselves in order to decrease consumption, needs for the energy, birth rates or any other number that is taking this civilisation into the zone of self-distruction. Even knowing the main problems, 99% of the people are just too selfish to make any changes in their own lives. So, there is no light at the end of the tunnel.

Posted by Ivana on 26 Oct 2011

The biggest problem man faces is is greed and capitalistic expectations. If we did not expect to have every type of food from all over the world in the local supermarket, became more self sufficient in the production of healthy foods, reduced our intake of red meat(mammals) and gadgets we would not have to export coal etc. all over the world to industrialist contributing to climate change.

In the long term however nature might just have it's way, however ingenious man might be and reduce populations dramatically like the black plague did in Europe!

Posted by William Maliepaard on 26 Oct 2011

Here is an article discussing what I initiated above on what could be the total inverse of what is predicted in your article above and it is very possible!

Posted by William Maliepaard on 26 Oct 2011

Great article. I'm happy to see that I'm not alone in being very concerned about the population explosion. Currently I'm enrolled in a Biology class at our J.C. and our instructor is very adamant and vocal about over-population.

I personally believe that too many religious leaders are brain-washing a dumbed-down populace in believing that large families are needed. If people aren't educated soon enough and women not empowered to take control of limiting family sizes then it might come down to governments requiring sterilization. Population-control can't wait another day! I decided at the age of 20 that I didn't want any children and I stood by that conviction--I am also an atheist.

Posted by Art Bock on 26 Oct 2011

Human beings are facing a crisis if measures are not taken to conserve the environment. young people are asked to take initiative by planting more trees.

Posted by isaac melly on 30 Oct 2011

Very good article. In this country, and maybe elsewhere, the left feels too guilty to even discuss this coming catastrophe and the right has'nt figured out that it will only bring more dreaded regulations (which we need)! Increasing regulations and restrictions need to be discussed as one of the many overwhelming impacts of overpopulation.

It is somewhat encouraging to see more discussion of this most important issue.

Posted by Greg on 01 Nov 2011

Thank you for this wake up call, similar to Moustafa Tolba`s UNEP alert in the late 1980`s. "We have about 20 years to turn around the climate trends after which it will be very difficult." Despite efforts on the science side, the political side has largely "lost it."

Those of us on the resource environmental management side (40+ countries personally) are pursuing solutions through adaptation, knowing that population growth in many regions it running away and leading to this forecast by a very senior Canadian scientist (retired of course). "Climate change will go its course global human population will drop by half, and then we will adapt."

Through international discussions such as Rio+20 June, 2012 and the Globe Environment Business Conference (Vancouver, March 14-16, 2012), I personally hope that we can nudge the influencers and decision makers to action who may feel stuck as we face such an uncertain future.

Patrick Duffy, Vancouver, Canada

Posted by Patrick Duffy on 08 Mar 2012

Those against the future population population projections need to develop a custom of appreciating the significance of vital statistics.

I also support the move by all governments to have an action over this explosive population growth if better life is expected.

Posted by KIMBUGWE DEO on 07 Nov 2012

The issue needs to be addressed/considered centrally as opposed to the peripheral approaches we tend to try to institute.

We (humans) are animals and thus our primary instinct (as a species) overrides intellectual considerations.

As all species we are self-centered and our consideration is not for the whole but rather for us. We are specist.

I believe that we (as an species) are not capable (due to instinct) of controlling our growth any more than parasites are capable of controlling their growth even if self destruction is inevitable.

Posted by arjuna dissanayake on 15 Nov 2012



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