The role of population growth during three decades of increasing carbon emissions

By Lucia Tamburino and Philip Cafaro | 21 March 2023
The Overpopulation Project


How often have you heard some version of this claim: “population growth is not a problem for climate change, because populations are growing in poor countries whose contributions to global emissions are negligible”? It gets repeated like a mantra, soothing words that banish thought. But what justifies a claim is not the number of times it is repeated, but the evidence supporting it. In a new study, we analyzed carbon emissions and demographic data from the past three decades and found evidence for a very different claim.

A dominant narrative in climate change debates asserts that addressing population growth is not relevant for climate mitigation. Population is only growing in the poorest countries, whose contributions to global carbon emissions are negligible, while the largest contributions come from rich countries, where the population no longer grows (or so they claim). Talking about population growth would hence be a dangerous distraction from the “real cause” of climate change: over-consumption in rich countries. It is inferred that addressing excessive consumption among the rich would be sufficient to deal successfully with climate change.

An underlying assumption of this narrative is that the world can be divided neatly into rich and poor. Although common, this view is obsolete and does not reflect today’s reality. As figure 1 shows, when we look at per capita income, the world’s countries form a continuum. Most are neither very poor nor very rich, but somewhere in between.

Figure 1. Life expectancy graphed against income for the world’s countries, 2018. Circles are proportional to population size. Source: Gapminder.

A common and useful categorization among economic analysts is the World Bank’s division of countries into four income groups: high-income, upper-middle income, lower-middle income, and low income. As you can see in Figure 2, the high-income group includes not just Western but also Arab nations (some of which are the richest), Japan, South Korea and several other countries in Asia and Latin America. The upper-middle group includes not only China but also Russia, Mexico and most countries in Latin America, and several countries in Europe and Africa. Africa is usually perceived as a poor continent, but it is actually quite varied, with the majority of the world’s low-income countries, but also many countries in the two middle groups, as well as a few small countries in the high-income group (e.g., Seychelles).

Figure 2. World countries according to the World Bank’s division into four income-based groups as of 2019: low-income (<1035 current US$ average GNI/capita), lower-middle-income (US$ 1036–4045), higher-middle-income (US$ 4046–12,535) and high-income (>US$ 12,535). Source: Tamburino, Cafaro and Bravo, An Analysis of Three Decades of Increasing Carbon Emissions.

So, with a more detailed and up-to-date picture of national income and wealth, how does the common hypothesis about population’s unimportance to carbon emissions hold up? Poorly, it turns out, as we report in a recent study in the journal Sustainability, “An Analysis of Three Decades of Increasing Carbon Emissions: The Weight of the P Factor.”

The evidence

Looking at emissions data, it is true that the low-income group’s contribution to global carbon emissions* is negligible: only 0.6% every year (average over the last three decades; see Table 1). But population isn’t growing only in the poorest countries. It is also growing rapidly in the two middle groups, with the large majority of global population (76%). The argument that “population growth in poor countries is not worrisome, because poor people do not impact carbon emissions significantly,” does not apply to these middle countries: their carbon emissions are significant! Indeed, the upper-middle group currently emits the most carbon of any group: 51% of the global total. Together, the two middle groups contribute more than 64% of global carbon emissions, almost two-thirds of the total. Moreover, the two middle groups are also the groups that currently are increasing their emissions the most, both total and per capita. The upper middle group is indeed the major contributor to global emission increases (see Table 2).

Table 1. Carbon emissions in 2019 by national income group. Source: Tamburino, Cafaro and Bravo, An Analysis of Three Decades of Increasing Carbon Emissions. *Note: data refer to EN.ATM.CO2E.KT, World Bank code for carbon dioxide emissions from the burning of fossil fuels and the manufacture of cement. They include carbon dioxide produced during consumption of solid, liquid, and gas fuels and gas flaring. They do not include carbon emissions due to land use change.

Population is also growing in the high-income group, despite the existence of a few wealthy countries where population is stable or slightly declining, such as Japan. Causes of growth around the world are different: in some cases a mix of demographic momentum (many young people, expected to produce children) and immigration, in other cases a combination of demographic momentum and high fertility. In contrast to the common cliché that only poor people have lots of children, fertility is above the replacement rate not only in the low-income group but also in the majority of lower-middle countries and in around one half of the countries in the upper-middle group. Notably, all African countries in the upper-middle group have high fertility, including three countries with fertility rates >3 and one with a fertility rate >4 children per woman. Surprisingly, there are also some rich countries with fertility above the replacement rate: Kuwait, Israel, Oman, Panama, and Saudi Arabia.

Regardless of the causes, population is still growing in all four income groups, albeit at different rates. During our study period (1992-2019), population increases ranged from 18.5% in the high-income group to 110.2% in the low-income group.

Has this population growth been important in driving recent greenhouse gas emission increases? IPCC Assessment Reports have repeatedly answered “yes,” identifying population growth and economic growth as the two main drivers of climate change. Our study confirmed this finding for the period 1992 to 2019. We compared the contributions of per capita emission changes, population change, and their interaction on total greenhouse gas emission changes (for methods, see the original article). The resulting contributions for all four country groups are shown in Table 2.

Table 2. Contribution of population change, per capita emissions change, and the interaction of the two to carbon dioxide total emission variations from 1992 to 2019. For each country group, contributions are shown in CO2 millions of tons (Mt).

Per capita emissions increase was the most important driver for the rise in CO2 total emissions only in the upper-middle income group, accounting for 63.6% of the total increase. Even for this group, population increase was also a significant factor, accounting for 18.8% of the total increase. Population growth was more important than per capita emissions increase in driving total increase for all the other groups.

The case of the high-income group is especially revealing. These countries represent around 16% of global population and are responsible for 35% of global carbon emissions. They have the highest per capita emissions and need to reduce them. Good news: they have been doing it! In the last three decades, most rich countries reduced their per capita emissions and there has been an average decline in per capita emissions in the high-income group (see Fig. 3, first panel).

Bad news: these countries failed to reduce their total emissions, which increased over our study period, although to a much lesser extent than in the middle groups. This indicates that even if population growth in high-income countries was low compared with other groups, it was sufficient to nullify the effect of reductions in per capita emissions. Not only was population growth responsible for the full increase in total emissions, it was also responsible for the missed decrease that could have happened over these last three decades thanks to reductions in per capita emissions. Figure 3 summarizes variations between 1992 and 2019 in total and per capita carbon emissions and in population, for the four income groups and for the world as a whole.

Figure 3. Carbon emissions in 1992 and 2019, for all four income groups and the world as a whole. The x-axis graphs per capita carbon emissions in tons/capita; the y-axis graphs population in billions of people. Rectangle areas hence represent the total carbon emissions in 1992 (green rectangles) and 2019 (transparent dotted rectangles). Source: Tamburino, Cafaro and Bravo, An Analysis of Three Decades of Increasing Carbon Emissions.

Facing reality

Population growth thus emerges as a major driver of climate change in all country groups, especially the high-income group. More than a dangerous distraction, it seems the elephant in the room that politicians refuse to deal with.

Unfortunately, not only is there a strong reluctance to recognize population growth as one of the drivers of climate change, in many countries there are active efforts in the opposite direction. Low-fertility countries that are moving towards demographic stabilization or decline, instead of embracing these trends, often try to boost their populations through pro-natalist or high immigration policies. This is happening in China, for example, which recently implemented a “three-child” policy, as well as in wealthier nations where demographic stabilization is typically presented as a problem.

Paradoxically, many of these same countries declare their will to reduce carbon emissions, through technological changes or reduced consumption. But reducing per capita impacts and boosting population at the same time is like weaving a canvas by day and unravelling it by night. As wise Penelope knew, such a process will never lead to a finished weaving—or, to leave the metaphor, actually reduce emissions. It indeed risks increasing emissions, which is what happened in the rich countries over the past three decades. Can we afford to let it happen again, during the next three?

Reprinted with permission from Frank Götmark – Project leader of The Overpopulation Project (TORP); Professor, Animal ecology and Conservation Biology, University of Gothenburg.

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