Population and climate change
By: Emmanuel Pont
Tags: Ecology, Demographics, Climate Change, Population

This is all the more regrettable as the authors insist just afterwards (WGIII 1.3.1 p129, but not in the synthesis) on the limits of the global analysis and the important local differences, while the rest of the report (notably WGIII 5) proposes much finer breakdowns. I would like to see the result of the calculation by country, then summed up on a global scale. Here is the IPCC one by major region, where we can already see a significant drop in the population factor:

Asia should be broken down even further: between 2000 and 2015, 60% of the global increase in emissions was in China. Chinese emissions increased by 151%, population by only 9%.

It is better to be very careful with the concept of “world population”, which mixes extremely different situations. Even at the country level it is often questionable. For example in India a poor rural family with a high birth rate will be mixed with an urban middle class family which consumes more and more but with a fertility rate below the European average.

How to reduce emissions?

We have just seen that it is very delicate to measure the “share of responsibility” of the population on emissions, so we cannot be satisfied with simplistic reasoning such as “population is a problem, so we must reduce it”. Yes, the world’s population exploded in the 20th century, that’s a fact and we can’t change the past. The relevant question is: today (rather than 50 years ago), what can be done and for what result? Applicable measures must be defined and evaluated.

Let’s start with the obvious: if there were half as many of us, all other things being equal, humanity would emit half as much greenhouse gases, and produce half as much pollution overall. This line of reasoning is so common that it could be the plot of a mainstream film. But common sense can be misleading. The rebound effect may be very large, it may be a world where everyone goes to Ibiza for a weekend, while emissions per person in the US are twice the average in Europe, for a very similar standard of living. At the current rate of emissions growth, we would quickly reach the same level. It is doubtful that humanity will be able to act before it hits the wall. It would be enough to “eliminate” the richest 10% to achieve the same result on emissions, as we saw earlier. And of course, you can’t just wipe out human beings with the stroke of a pen. We must ask ourselves what are realistic and ethical ways to act on demography and emissions.

How can we go further and link emissions and population numerically? We will start with a simple equation, the Kaya identity, which breaks down emissions by individuals⁶ :

Emissions = number of people x emissions per person

It is an identity, it is necessarily true, but that doesn’t necessarily make it relevant either. You could, for example, break it down by tomato production numbers, and it would be just as true but irrelevant. On population and climate, if Qatar is at the top of the emissions per capita ranking, it is not because of the decadent lifestyle of its inhabitants (85% of whom are precarious immigrants from poor countries), but because of its large gas industry.

An obvious conclusion from this equation is that reducing population by 10% and emissions per person by 10% have the same overall effect (this is actually an approximation, the variables are not independent). So we can use it to compare measures⁷, putting aside the ethical complications of comparing a life and a trip to Bali on their respective carbon footprints.

So, how useful would reducing the population be for the climate? To find out, we need to simulate finely the respective evolutions of population and emissions per person. I have only found one recent study (2010) answering the question: “Global demographic trends and future carbon emissions”. This is the study that is quoted everywhere on the subject, but often to the 2nd or 3rd degree.

This study uses the IIASA emissions scenarios, a complex economic model, and the difference between the UN’s high and medium demographic scenarios. However, it only takes into account CO2 and not all greenhouse gases, which underestimates the share of countries with high birth rates (2% instead of 3.5%). After calculations, the result of the study is a 16% difference in emissions in 2050 in a “business as usual”⁸ scenario:

What exactly does this result tell us, why does China have so much weight, and sub-Saharan Africa so little? Remember the UN high scenario, the one that is achieved by increasing the overall fertility rate by 0.5. This scenario does not correspond directly to any plausible projection or applicable policy, but does have a much greater effect in countries with low birth rates and high emissions, such as China, than in those with high birth rates and low emissions. This study therefore says absolutely nothing about the demographic transition or the real scope for reducing emissions by acting on the population, contrary to what the summary suggests: “we show that slowing population growth could provide 16–29% of the emissions reductions suggested to be necessary by 2050 to avoid dangerous climate change”. This should be understood to mean “if fertility falls by 0.5 worldwide”, which is therefore purely theoretical. No one is proposing to lower fertility in China by 0.5, when it is only 1.6 children per woman today, and this would have absolutely nothing to do with the demographic transition. This may be obvious to specialists of the field, but not to the rest of the world.

Unfortunately, this is the original source of this call by thousands of scientists to, among other measures, limit population. Here is the chain of quotes:

This should not be seen as a conspiracy or an evil plan by Brian O’Neill, but rather as a game of “Chinese whispers” that increasingly over-interprets a limited initial scientific result. Ironically, the mainstream article has the worst headline but is more accurate in substance, calling for a general population reduction without mentioning the demographic transition. The declaration, which does not explicitly mention it either, refers to means of action that are exactly those of the demographic transition. The most misleading article in this chain is probably the one in Science, which goes to great lengths not to use the term “demographic transition”⁹ even though it only describes countries with high fertility, and acts as if these countries would contribute to the calculated reduction of emissions (the author is the same and should know this from his previous result). Yet this article acknowledges, without going further, that per capita emissions are low where conventional demographic measures can lower the birth rate. There is another missed opportunity in the 2012 paper, which notes that some measures on demographic transition would result in a decline in fertility close to the 0.5 variation of the UN scenarios. So why not repeat the 2010 calculation and apply it only to relevant countries ? I will do it very roughly (the data table is no longer available, so I had to measure pixels on the graph and extrapolate Africa): it would be around a 1% reduction in total emissions by 2050. It is not zero, but it probably doesn’t deserve to be a top priority action¹⁰.

Drawdown is equally bad on the subject: it similarly takes the difference between the high and medium scenarios (while acknowledging this construction as arbitrary on the site). It then splits the effect between family planning and girls’ education in half (even though there are many more factors in the demographic transition). The total comes second in the “list of solutions”, feeding the illusion that the demographic transition is a priority climate issue. No, fertility in rich countries, which are the main emitters, will not be reduced by 0.5 by increasing girls’ education and family planning…

We have previously calculated that the countries in demographic transition account for around 3.5% of total global emissions. The IIASA scenarios used in the previous study project strong economic growth for these countries, but without catching up at all with the developed countries, which also continue to grow. The figures are not broken down by country, but Africa as a whole rises from 6% of global CO2 emissions (including 1% for inter-tropical Africa, the region with the highest birth rate today) to 8% in 2050. Whatever the room for maneuver on the demographic transition, the difference in terms of emissions will be small. However much we may fear that our unsustainable standard of living will catch up with that of less developed countries, it is far too slow today, and probably in the near future. This is the main explanation for its slow demographic transition: intertropical Africa is not developing fast enough.

Should poor countries be helped to accelerate their demographic transition?

We have just seen that the demographic transition of “poor countries” is in fact a very secondary problem for greenhouse gas emissions. Not necessarily uninteresting though, because this meagre result can be achieved very effectively, for example it would only take $6 billion per year to make contraception widely available throughout the world, for about 20 million fewer births each year. If we estimate the result at 1% reduction in emissions in 2050, as calculated previously, this is probably one of the most effective measures available. Unfortunately there are very few low hanging fruits of this order.

However, the main climatic fact for these countries is that they will also be the most vulnerable to global warming, and a higher population will amplify the difficulties. This is particularly the case in the Sahel, which is already suffering from the combination of global warming and population pressure.

Population remains a critical factor when the problem is extended to the environment as a whole, including water, soil, deforestation, biodiversity, waste, etc. In particular, there are smaller gaps between “rich” and “poor” in these areas than for emissions¹¹ :

Although it has been calculated that Africa is on average much less dense than Europe, if the deserts are removed, the density of inhabited areas is not so far off, and human expansion will be to the detriment of local natural areas, particularly forests. Many countries in the process of demographic transition already lack water and food production and are rapidly degrading their ecosystems:

Poorer countries must therefore be helped to achieve their demographic transition, but first and foremost for their own sake and that of their environment, not to reduce global warming. This avoids the neo-colonialist overtones of the infamous “we must first limit births in poor countries rather than review our lifestyle”¹². This is all the more interesting because in these countries the reduction in population growth should also result in economic growth, unlike most ecological measures in rich countries.

Is it necessary to control the population in rich countries?

We have seen that rich countries are responsible for the vast majority of greenhouse gas emissions, so reducing their population there would have a significant effect, especially if the reduction affects rich individuals. The great difficulty is to know how, for what political acceptability, what result, and what timeline.

For countries at the beginning of the demographic transition, the main policies are known, but they are unanimously accepted and already applied in the majority of cases (within the limits of the often limited resources of states). It is possible to extend them but there will be no miracle: development takes time. A few rare short-term measures can be effective but not sufficient, for example in Africa 1/4 of women want contraception but do not have access to it. Authoritarian limitation of the number of children has only been adopted by two countries in the world, China and Vietnam. The debate is still open on the real effectiveness of the one-child policy in China, as fertility had mainly decreased before.

For countries at the end of the transition or after, the vast majority, it is much more complicated: measures that are both consensual and effective have been exhausted. The level of education is already high, women are fairly well integrated in the labour market, pensions are assured, and contraception is widely available… Moreover, fertility rates are still falling in most of these countries, often well below the sub-replacement threshold. The only ways to further reduce fertility would be through cultural changes and authoritarian measures. The former are very slow and unevenly distributed, with the latest measurement of the desire for children in the US above 2.5 children per couple. The latter seem very far from being politically acceptable today¹³. The demographic transition has been very fast in some countries (e.g. Iran) but it seems much easier to convince people to go from 6 to 2 children than from 2 to 1 or 0.

What would be the effect of limiting births, whether it happens voluntarily or authoritatively? I have only found a calculation at the global level, which is not really helpful because of the wide variety of situations. One can quickly calculate an order of magnitude, here for France which is a good example for rich countries with a 1.9 fertility rate. The number of children per family is available on the INSEE website (you have to extrapolate the details for families with 4 or more children). Banning children above 2 would mean reducing the total number of children in families by 13%. This figure is falling rapidly, the previous census gave 15%, so I estimate that this would be equivalent to a drop in births of around 10% today. This low figure is not surprising, with an average fertility rate of 1.9 there are not that many children above 2. All that remains is to compare this scenario on the INED simulator (in free simulation mode) with the one without modification.

Result: -5% of population in 2050. This does not take us very far, and again the calculation has been broad. As the fertility rate keeps falling, the number of children over 2 will continue to decrease too, and we have forgotten all the annoying details such as twins and other multiple births, separated or reconstituted families, or children of rape, an explosive subject in the United Kingdom, which has reduced benefits over 2 children.

What about the benefit cuts promoted by some associations? It will be less than 5% in any case. The British government has not given an estimate of the expected effects on demographics, but cites a study on the large increase in benefits in 1999. It measures an increase in fertility of 15%, but only for the poorest 20% of the population, which means an increase in the total fertility rate of 3%. By simulating an equivalent reduction, we arrive at an order of magnitude of 2% less population in 2050.

To achieve a significant effect we need to move to a one-child policy, bearing in mind that it would probably be extremely unpopular. In this case we arrive at a population reduction of about 19% in 2050, but welcome to a world without youth¹⁴ :

And just out of curiosity, what would happen if everyone gave up having children? A 36% reduction in population by 2050.

In short, I strongly doubt the political possibility of significantly and rapidly reducing the population by acting on the birth rate in France, and more generally in rich countries that have completed their demographic transition.

The other “possibility” remains a sharp increase in mortality from war, famine and disease, which nobody wants. Let us remember that these events are not simply a “numerical reduction” of the population, but profoundly destroy society. This is what is likely to happen in Africa, which remains the most fragile continent economically, politically and ecologically.

Beware, if we apply the result of these calculations directly to the Kaya equation, we are acting as if all individuals had the same carbon footprint, whereas in practice it varies greatly by income and age, and is much lower for children and young people in particular:

Our estimated figures therefore clearly overestimate the reduction in emissions, because by 2050 it is mainly children that would have been avoided.

So, what concrete measures can be taken to reduce emissions?

We are going to calculate them in France to try to reach the objective of carbon neutrality in 2050, which requires dividing our total emissions by about 7 (the French government’s objective is between 6 and 8). We arrive at the easy-to-remember figure of one tonne of CO2 equivalent per inhabitant per year, which is the level today of Bangladesh or Madagascar¹⁵. Dividing by 7 in 30 years is to reduce by a little more than 6% per year, and still we do not count imports, which increase the average French person’s carbon footprint by 50% (i.e. a division by 12 to reach carbon neutrality).

Should we look later than 2050, when demographic measures will have more effect¹⁶? There is no “scientific truth” on the matter but I think not, for several reasons:

The environment does not wait, it is already deteriorating very quickly, with a significant inertia and risks of runaway change

The further we get into the future, the more uncertain the world’s evolution becomes, and the more likely it is that disasters will occur and fundamentally change the equation

The further we get into the future, the more we suffer from the negative effects of radical demographic measures, such as a predominantly elderly population

The further we get into the future, the less fossil fuel will be left to burn anyway

As we have seen, there will be no consensual measure on demography, and unpopular policies such as degressive benefits or even the two-child limit will have a small effect (-5% in 2050). Even the most radical measure, banning children entirely, reduces the French population by only 36% in 2050. I don’t see how we can do more without killing people, and we would still have to divide individual emissions by 4.5 (-78%) after this measure if we consider (generously) that it reduces emissions by that much. Let’s face it: the vast majority of the effort must be directed at per capita emissions, regardless of population growth, even if humanity gives up children tomorrow. And to divide these emissions by 4, 7 or 12, there are no miracle: small improvements are far from being enough, profound changes in our way of life, our economic system and our culture are needed. Remember that one tonne of CO2 per person per year is the number for Bangladesh or Madagascar.

There is no “scientific truth” about the ease of implementing this or that measure either, but I will let you judge by comparing my estimates for France (which are probably overestimated) with the measures proposed by the Shift Project for Europe, which I have recalculated in relation to total emissions²² :

Today it seems to me that it is politically easier to close down coal-fired power plants than to introduce the one-child rule, which looks very far from being acceptable. A total ban on children will probably never be acceptable. Population control has often been a channel for oppression and human rights abuse. The only measure implemented in rich countries, the suppression of benefits above 2 children, is already extremely unpopular even though it is not coercive. Convincing people seems to be very slow.

Are the measures to achieve carbon neutrality so harsh that they would take us back to the Middle Ages, which might lead to a preference for limiting children to mitigate it? Probably not. It should increase a number of costs and require huge investments in low carbon technology (notably energy and transport), but even low energy scenarios can offer a decent standard a living. There has been little reduction in emissions today, but if you broaden it to the ecological footprint, there are already “sustainable” countries with a high human development index. The stars of these rankings are unexpected countries like Costa Rica or Cuba:

What to do as an individual in a rich country?

On a personal level, should you give up children to reduce your carbon footprint? You may have heard of the carbon legacy without knowing its name, for example in the following articles:

Here is the associated graphic: