Pop Goes the Climate Problem

Well, not exactly. But this new paper in PNAS, which is bound to make make a splash, finds that

slowing population growth could provide 16-29% of the emissions reductions suggested to be necessary by 2050 to avoid dangerous climate change.

What surprises me most about the paper’s findings, as Grist reports, is that urbanization

can push emissions up by more than 25 percent, particularly in developing countries, because “urbanization tends to increase economic growth.” This trend is strong enough even to outweigh the energy-efficiency benefits of city living.

That’s so striking that I wonder if there’s going to be some push back from scholars on this. The other thing that I found odd about the paper is this sentence:

For example, change in U.S. population growth has a pronounced effect on emissions, despite its small contribution to global differences in population outcomes, because of the relatively high per capita emissions implied in the B2 scenario.

I take this to mean that it’s not the overall spike in world population that matters, it’s the carbon footprint, of which we know that the U.S. has the biggest. So about that population problem…

Seriously, am I detecting a weird contradiction here, or am I over-analyzing the study’s findings? The paper is freely accessible at PNAS, so if this sort of debate floats your boat, go have a look and then come back and set me straight.

14 Responses to “Pop Goes the Climate Problem”

  1. Keith, interesting find.

    What you see as a weird contradiction is only contradictory in a black and white world. Population growth and carbon footprint are both important in influencing total emissions, so there is no contradiction that I’m seeing.

  2. Sashka says:

    slowing population growth could provide 16-29% of the emissions reductions suggested to be necessary by 2050 to avoid dangerous climate change.
    Duh. Don’t know about 16-29% but the concept is fairly obvious, isn’t it?
    urbanization can push emissions up by more than 25 percent, particularly in developing countries, because “urbanization tends to increase economic growth.”
    This doesn’t make sense to me. The way I see it, urbanization is a byproduct of economic growth and industrialization, not the cause of it.

  3. Jack Hughes says:

    Hi Keith,
    Have you ever seen one of those jokey emails where they prove that Santa Claus has to travel at mach 4 to get round 2 billion kids in 5 continents in 24 hours on Christmas Eve?
    These bogus projections always remind me of that – without the humor. They just invent the numbers and then admire themselves. Some invented number may be between 16% and 29% of some other invented number. Well, guys, 29% is nearly double 16% – so do you have a clue about anything at all ?
    It looks like those job ads where the salary is “between $30k and $55k” – it means nothing.

  4. Tom Fuller says:

    The paper is right about growing numbers living in cities being a net contributor to energy use in developing countries.
    Cities are less energy intensive than rural or suburban environments. However there are several factors at play when people move into cities, and these are more pronounced in developing countries.
    The obvious one is increasing income leads to quick adoption of energy using appliances–the refrigerators, washing machines, cars, televisions, even the odd computer here and there.
    Equally as important are the changes in household composition, as family size shrinks significantly, which surprised people looking at Asia, as they felt (wrongly, as it turned out) that families would stick together more. But smaller household sizes (small apartments, mostly) led to newly urbanized families not letting an endless horde of cousins couch surf indefinitely.
    So, while New York City only uses 1% of the U.S. energy total, the same is not true in the developing world.

  5. Jack Hughes says:

    Hmmm – guessing about the world in 40 years time. Just think what guesses from 1970 would be like today:
    Paul Ehrlich was talking population bomb.
    Schneider was talking global cooling
    Berlin Wall still standing
    Home computers ?
    Cell phones ?
    Blogs ?
    Global cooling ?
    I don’t even think there was an environment in 1970…

  6. Keith Kloor says:


    I recognize that population and consumption/lifestyle each play a role, I just don’t see them being equal.

    I also admit to being as perplexed as Sashka about the urbanization finding. I’d like to see some discussion of this at other blogs or in any news articles.

  7. intrepid_wanders says:

    I am surprised that you get your carbon information from UCSUSA.  I have no idea where they get their numbers from since they do not cite a source, but lets go to where the United Nations Development Programme goes, the Carbon Dioxide Information Analysis Center.  Fair enough?
    First off, the total emissions rank of the US at #2 works, but the numbers of the UCSUSA are way off.  Next, we go to the ranking per capita and  find the US at #11 and Australia at #12.  Again, numbers nowhere near UCSUSA numbers.
    Okay, back to the paper.  Using the data from CDIAC, if you look at the emissions of the US you will see that we have flat-lined, per capita.  If you look at growing economies like China or India, their per capita is sky-rocketing.  With a study that was looking at demographics, the per capita data was probably used for the model projections. In that cause, the standard deviation of China or India growth would bury anything the US, EUR would do to curb emissions.
    BUT, I found the article rubbish for the contraception plug again.  I am sure the PNAS editors and reviewers got excited about that.

  8. Ron Broberg says:


    using  “econ$” as total economic activity or GWP (gross world production)

    CO2 emissions = (population)* (econ$/pop) * (CO2/econ$)
    You can reduce the growth of CO2 emission by slowing population growth (1st term), slowing economic activity (2nd term), or making the economy more energy efficient  or less fossil fuel dependent (3rd term)

  9. Keith, indeed, what’s cause and effect is a bit unclear here. Though what Tom Fuller sais makes sense:
    “increasing income leads to quick adoption of energy using appliances”“the refrigerators, washing machines, cars, televisions, even the odd computer here and there.”
    That could be an explanation as to how urbanization tends to lead to economic growth and increased emissions. I.e. people move from the poor countryside to the city in order to try and improve their economic wellbeing. Inasmuch as they indeed grow richer their emissions will increase as well.

  10. Pascvaks says:

    The ultimate ‘solution’ to the AGW problem has always been population reduction.  Well, I guess, we’re finally talking about what really matters (to those with such a mad raving concern about doing something quick so we don’t cook the planet in 50 years).

  11. kdk33 says:

    Readily available low cost energy (ie fossil fuels) makes possible modern life – wealth, health, things like that.  So someone has discovered that expanding the modern lifestyle will… use more energy.

    2+3=5  and 3+2=5.

    But I guess it’s fun to argue about.

  12. Pascvaks says:

    I have no doubt that our progency will one day discover the Warp Drive, and I do not doubt as well, that they will extablish a MAX  CAP for each planet they colonize.

  13. Pascvaks says:

    Judith Curry is discussing a related issue on her blog at
    In that piece she refers to a PielkeJr link to the following “calculator” at

    In our current situation (Scale 1:World) it appears that the easiest way to get from “here” to “there” in the Ol’ Global Warming Game is population reduction.  Try it.  It does one good to see what, for some in the game, the ‘Bottom Line’ in the APG issue is all about.  (It does, that is, if you’re inclined to be rather brutal about tough people problems and it does add up –well that’s what the calculator says.)

  14. JohnB says:

    Am I the only one that has noticed that every solution for every ecological problem for the last 30-40 years seems to involve keeping those nasty, overpopulating black people in the Third World in Third World conditions?

    It always comes down to;
    1. They must cut their population. (Compare the population densities of Africa and Europe and see which is higher.)
    2. They must not be allowed to develop. (That will increase CO2 emmissions, or pollution, or something.)
    3. They must not get access to better medicines and education. (That will mean that more of them will live.)

    If there is anything more racist and genocidal than the modern “Green” movement, then I don’t know what it is.

    From DDT onwards it is always the planets “darker” population that must live in poverty and despair and preferably die off in large numbers to appease the “Green” agenda.

    And yes, they do it to Australian Aboriginals too.

    The common thread is that the people condemned are always dark.

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