Overpopulation isn’t the Problem

Some folks in Boulder like to make analogies to exponential global population growth in discussions about our local land use decisions (see for example Frosty WoolridgeFrosty Woolridge again, Robert Baker, David Brandt, or the venerable Al Bartlett himself). These analogies are inappropriate in multiple ways.

First, steep declines in fertility worldwide have largely defused the population bomb. Second, even if the bomb were still ticking, the population changes we see in Boulder, and more generally the Front Range of Colorado, the US and the booming megacities of Asia aren’t about population growth per se, they’re about migration.  In the developing world, it’s migration from rural areas to cities. In the already rich countries, it’s mostly migration between cities, often from low-wage regions to areas with better jobs and higher quality of life. Or it would be anyway, if we actually let people build housing in those places.

How we choose to build and rebuild cities to accommodate these migrations and humanity’s peak population later this century will largely determine our ultimate impact on the Earth’s climate and biosphere, and the quality of life that humanity has access to.  Contrary to many “population bomb” narratives, the main problem here as it relates to climate isn’t the impact of large numbers of poor people, because small numbers of rich people are responsible for the overwhelming majority of current greenhouse gas emissions.  How we accommodate those wealthy, high emissions populations makes a big difference, both directly, and through the example it sets for the rapidly expanding global middle class.

Humanity Defused the Population Bomb

Thankfully, global population growth isn’t the problem in 2016 that it was when it helped inspire Boulder land-use policies 40-50 years ago; we live in a profoundly different — and in many ways better — world. As Swedish demography rockstar Hans Rosling has been saying for years via his Gapminder project, we need to take care to constantly upgrade our worldviews with current data.  Especially on population, Boulder’s cultural narrative is woefully out of date.

Globally, human health and access to education have improved radically over the last half century, especially for women.  As a result, the total number of children a woman would expect to give birth to on average over her lifetime dropped from 4.7 in 1970 to 2.5 in 2014. That means worldwide fertility in 2014 was the same as US fertility in 1970. India, Bangladesh, Mexico, Brazil, and many other “developing” countries now have fertility rates well below that of the US in 1970. The one major exception is Africa, which still has a total fertility rate of 4.7 (the same as the global fertility rate in 1970) but even African fertility rates  started falling precipitously in the last couple of decades.

All this means that outside of Africa, fertility rates are already on average just below replacement, and the remaining expected population growth results from young people who have already been born having their own children at replacement rates, and then growing old. Barring catastrophe, we’re committed to that growth demographically, and we will likely experience a peak human population of 9-11 billion people late in the 21st century.

This is kind of awesome! An unprecedented number of women worldwide are empowered to choose how many children they have. Global life expectancy is at an all time high, and infant mortality rates are at an all time low.  Yay humans!  But we still have to figure out how to (at least briefly) support 10 billion people on the one and only Earth we’ve got, and we’ve got to lift the poorest billion out of grinding $1/day poverty both out of basic human decency, and because that kind of poverty seems inextricably linked to high birth rates.

It’s Migration, not Growth

Almost any city in the world where we see rapid population “growth” today is really just getting its new people from somewhere else.  In Asia and Africa, it’s rural populations heading to cities for the first time, seeking different and hopefully better economic opportunities. This is the largest migration in human history. Between 2016 and 2030, the UN estimates that more than 1 billion people will move to cities, and by mid-century it’s expected that two-thirds of humanity will live in cities.

In the richer parts of the world most people already live in cities, and increases in local population are due to migration between them, often from low-wage, low-productivity areas to places where people can find better jobs.  In the US at least, there also appears to be a cultural shift underway, in which more people are attracted to the denser cores of our cities.

These migrations are a huge opportunity, because we’re going to be building or re-building urban infrastructure for more than 2.5 billion people over the next 35 years, and the design of our built environment predetermines a huge proportion of our resource consumption.  It says how much energy is needed to heat, cool, ventilate and light our buildings, how much energy it takes to move goods and people around, the type and quantity of materials consumed per person in constructing infrastructure and the buildings themselves, and (at least in the rich world) how many semi-disposable, seldom used consumer goods we’re able to let pile up around us.

The difference between a sprawling exurban metro area like Atlanta (or Denver) and a compact walkable city like Barcelona is a factor of ten, in terms of transportation energy consumed per person.  Given that Atlanta takes up ~25 times as much land area, it’s not hard to imagine that there’s around 10 times as much material and embodied energy locked up in its infrastructure too.


Update 2016-07-01: See the comments section regarding the data behind the comparison of Atlanta and Barcelona. The population numbers on this image, which came from the Washington Post may not reflect the urban areas being discussed, but the general statement that there’s an order of magnitude variation in the GHG emissions associated w/ different types of cities holds true.  For example, here’s another comparison of Barcelona and Denver:


If we’re creating a new city, or reconstructing an existing one to accommodate new people, there’s a factor of 5 or 10 improvement to be had in the energy it takes to operate our buildings.  According to the Dept. of Energy, buildings are responsible for about 40% of US energy consumption, and a little over half of that energy goes to heating, cooling, lighting, and ventilation, loads related to the building itself, not the activity that takes place inside it.  Nearly airtight, highly insulated buildings that avoid thermal bridging, and use heat recovering ventilation systems, like those that meet the German Passivhaus standard use 80-90% less energy in their operation than typical existing buildings.

Whether or not we can muddle through a peak population of 10 billion will depend on what kind of prosperity we try to create, and whether we in the wealthiest enclaves of the world cling desperately to a hyperconsumptive way of life that others try to emulate.

Is it them, or is it us?

With most of the new urbanization taking place in Asia and Africa, you might think what we do is irrelevant, but carbon emissions aren’t evenly distributed — not by a long shot.  According to a 2015 study by Oxfam International, the richest 20% of humanity is responsible for nearly 70% of all emissions, while the poorest 50% accounts for only about 10%.

Screen Shot 2016-06-28 at 9.35.18 AM

To me this says there’s a lot of room for prosperity in the middle of the world’s income distribution.  A $1/day existence is no shoes, and subsistence agriculture holding starvation at bay.  A $10/day existence is decent public health measures, clean water and enough food, high literacy rates, bicycles and cell phones.  But is there any room at the top, where we make $100/day or more? Not like we do it today.  Vaclav Smil says it well:

So to me Boulder’s land-use regulations that prevent us from creating more low-consumption households are a moral failure.  We’ve codified mandatory systemic consumption — large homes on large lots that are illegal to share, and too sparse to support transit, too far from jobs and services for most people to walk in a utilitarian way.  The resulting predictable dominance of the automobile makes our streets hostile, and reinforces car-dependence, even among those who would prefer to make other choices.  It’s an environmental catastrophe.  Solar panels are great — and we need trillions of watts worth of solar worldwide — but in places like Boulder, it would be greener to just build more dense housing.

3 thoughts on “Overpopulation isn’t the Problem”

  1. I’m sorry, but you are screwing up numbers big time! Barcelona itself has only a population of 1.6m. The greater area has a population of roughly 5m, but it’s also a little bit bigger: 3’236sqm and there’s a lot of commuting going on. You are not going to save the world with such numbers.

    1. The only point I’m making in that comparison is that urban transportation and infrastructure systems vary dramatically in the emissions they commit us to, and that on a per-capita basis, there can be around a factor of 10 difference, in transportation emissions, built infrastructure, etc. depending on how a city is built. Another reference that gets at the same point, with a less pretty graphic: Greenhouse Gas Emissions from Global Cities (2009) (full PDF here). Barcelona (city, area 100km^2, pop. 1.6M) is compared to Denver (city & county, area 397km^2, pop. 580K), with a very similar result as far as GHGs attributable to transportation per person as the Atlanta case, and overall a factor of ~5 difference in total GHG emissions per capita (though a fair bit of that difference is due to Barcelona’s reliance on France’s nuclear power for electricity)

      Global Cities per capita GHG Emissions

      The graphic comparing Atlanta and Barcelona above came from the World Resources Institute. Their original reference is this 2004 paper which has the Barcelona and Atlanta populations at 2.8M and 2.5M people, respectively, as of 1990, as does the WRI report that the first post is referencing. So I don’t know what’s up with the 5M numbers on that graphic. It appears to have come from this Washington Post story, and it looks like they might have just pulled the current metro area populations rather than using the 1990 numbers referenced in the paper (which may not have referred to the same exact areas).

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