Population in the IPCC’s new mitigation report

A new IPCC climate change mitigation report confirms that population increase and economic growth are the main drivers of today’s historically high greenhouse gas emissions. But that scientific information has been censored and removed from the Summary for Policymakers distributed to the world’s press and the public. Does a problem disappear if we don’t mention it?

by Philip Cafaro

Last week, Working Group III’s contribution to the IPCC’s Sixth Assessment Report on Climate Change came out. This “mitigation report” summarizes the recent scientific literature on the causes of climate change and current emissions trends. It also assesses humanity’s options to limit future climate change and the possible environmental impacts of different policies going forward.

Figure SPM.2 c: Net anthropogenic greenhouse gas emissions per capita and for total population, per region (2019). The height of each rectangle shows per-capita emissions, the width shows the population of the region, so that the area of the rectangles refers to the total emissions for each region. The blue, orange, and gray bars represent emission contribution from fossil fuels and industry, land use, and other emissions respectively. Source: IPCC, Climate Change 2022: Mitigation of Climate Change: Summary for Policymakers.

A recent opinion piece in The Guardian titled “Scientists have just told us how to solve the climate crisis – will the world listen?” calls the AR6 mitigation report “a major leap forward compared to previous reports.” “Climate scientists have just pulled off a truly impressive achievement,” Simon Lewis writes. “They have stood firm and persuaded the world’s governments to agree to a common guide to solving the climate emergency.” This might seem unduly optimistic, given that the report states clearly that humanity is on pace to increase average global temperatures by 3° to 4° C by the end of the century. But those governments have signed off on this report, Lewis argues, so “their citizens can now hold them to account for the failures it details.”

Lewis goes on to report that the new AR6 Summary for Policymakers breaks new ground by rejecting population growth as a driver of increased greenhouse gas emissions. He writes:

The last IPCC summary on solutions in 2014 labelled population growth as one of ‘the most important drivers of increases in CO2 emissions from fossil fuel combustion.’ Such dangerous misunderstandings are now gone. Seven years on, these old ‘blame the poor’ arguments increasingly seem like a relic of a previous age.

That got me curious. For decades, climate scientists have used the Kaya identity to explain changes in global CO2 emissions. In plain English, it reads: Emissions = Population x GDP per capita x Energy used per unit of GDP x CO2 generated per unit of energy. Based on this framework, past IPCC assessment reports have identified demographic and economic growth as the main drivers of climate change. Had that really changed? I decided to have a look at the IPCC’s new report.


The Scientists’ Report

The full AR6 Mitigation Report, the one written by the scientists, is 2707 pages long. I confess I didn’t read the whole thing. But I did read the first two chapters (of seventeen total). There the fundamental role of growth in driving higher GHG emissions is clear, as it has been in past reports. Chapter 2 of the full report, “Emissions Trends and Drivers,” notes (page 2-4):

Globally, GDP per capita and population growth remained the strongest drivers of CO2 emissions from fossil fuel combustion in the last decade (robust evidence, high agreement). Trends since 1990 continued in the years 2010 to 2019 with GDP per capita and population growth increasing emissions by 2.3% and 1.2% yr-1, respectively. This growth outpaced the reduction in the use of energy per unit of GDP (-2% yr-1, globally) as well as improvements in the carbon intensity of energy (-0.3%yr-1).

This paragraph is reiterated word for word in the 142-page Technical Summary to the main report (page TS-12), which was also written by the scientists.

The Technical Summary also notes that demographic and economic growth are likely to continue driving higher emissions going forward. It discusses this in relation to the so-called Shared Socioeconomic Pathways (SSPs) that model possible policy scenarios (page TS-41):

The main emissions drivers across the SSPs include growth in population reaching 8.5-9.7 billion by 2050, and an increase in global GDP of 2.7-4.1% per year between 2015 and 2050. Final energy demand in the absence of any new climate policies is projected to grow to around 480 to 750 EJ yr-1 in 2050 (compared to around 390 EJ in 2015) (medium confidence). The highest emissions scenarios in the literature result in global warming of >5°C by 2100, based on assumptions of rapid economic growth and pervasive climate policy failures (high confidence).

According to the scientists, then, population growth and economic growth are indeed the major drivers of increased greenhouse gas emissions. Population growth compounds the effects of increased wealth by the number of people enriched. Furthermore, human numbers will be a major influence on emissions going forward. To note just one more place in chapter 1 where the general point is made unambiguously (page 1-13):

Global GHG emissions have continued to rise since AR5, though the average rate of emissions growth slowed, from 2.4% (from 2000-2010) to 1.3% for 2010-2019. … Important driving factors include population and GDP growth. The pause in emissions growth reflected interplay of strong energy efficiency improvements and low-carbon technology deployment, but these did not expand fast enough to offset the continued pressures for overall growth at [the] global level.

Expanding on this general theme, there are numerous places, just in the first two chapters, where the authors state that future population growth could undermine mitigation efforts in specific economic sectors, including the industrial sector (page 2-47) and the agricultural sector (page 2-53). There is also a reminder of the ubiquity of population’s impacts on emissions, including in the developed world (page 2-42):

Population growth has also remained a strong and persistent upward driver in almost all regions (+1.2% yr-1 globally from 2010 to 2019), although per capita emission levels are very uneven across world regions. Therefore, modest population increases in wealthy countries may have a similar impact on emissions as high population increases in regions with low per capita emission levels.

This ubiquity is reinforced by figure 2-16 of the main report (below), which provides figures for regional changes in the four Kaya factors, showing their importance.

Figure 2.16 Trends and drivers of global GHG emissions, including b) share of total and per capita GHG emissions by world region in 2019, and c) Kaya decomposition of CO2 emissions drivers. The Kaya decomposition is based on the equation F = P(G/P)(E/G)(F/E), where F is CO2 emissions, P is population, G/P is GDP per capita, E/G is the energy intensity of GDP and F/E is the carbon intensity of energy. Source: IPCC, Climate Change 2022: Mitigation of Climate Change.

The Politicians’ Report

Given all this, how can Simon Lewis claim that the IPCC’s new mitigation report avoids the “dangerous misunderstanding” that population growth is an important driver of increased greenhouse gas emissions? The answer is simple: none of this discussion of population and economic growth made it into the 62-page Summary for Policymakers, which is all most people (including reporters) read. Unlike the full report, this document is vetted by political appointees. They apparently decided to censor anything that might call into question the goodness of continued growth.

For example, on page 2-4 of the full report, in the chapter on emissions trends and drivers, we are given three bold-faced statements laying out the general situation:

Global net anthropogenic Greenhouse Gas (GHG) emissions during the last decade (2010-2019) were higher than at any previous time in human history (high confidence).  

Emissions growth has varied, but persisted across all groups of greenhouse gases (high confidence).

Globally, GDP per capita and population growth remained the strongest drivers of CO2 emissions from fossil fuel combustion in the last decade (robust evidence, high agreement).

Pages 4-8 of the Summary for Policymakers repeat and elaborate on the first two sentences. But the third one is excised; instead, it skips ahead to the more congenial topic of regional disparities in greenhouse gas emissions.

We are thus left in the strange situation where the chief public-facing document from the IPCC’s new mitigation report, the one that most people will see, does not clearly identify the fundamental drivers of global climate change. This despite the fact that this important information is contained in the full report the summary is supposed to be summarizing.

As the Summary for Policymakers proceeds to consider policies to limit climate change, the two factors of the Kaya identity that are moving in the wrong direction vis-à-vis greenhouse gas emissions (population and affluence) are simply excluded from consideration. So it is not surprising that the words ‘contraception,’ ‘family planning,’ ‘overconsumption’ and ‘limits to growth’ do not appear. Meanwhile, measures that address the two technology factors (energy used per unit of GDP and carbon emissions per unit of energy) are discussed at length. They hold the field as the sole contenders for addressing climate change, not because they have been shown to be easier, cheaper, or more equitable to address, but by default.

Let’s be clear. Addressing overpopulation or the dangers of continued economic growth are not on the table, not because the scientists don’t discuss them in the full report. They do. They aren’t there because the politicians who censored the public-facing Summary for Policymakers don’t want to address them, or have their constituents discuss them.

Is this, as Simon Lewis claims, progress? Or just the latest example of our inability to address climate change honestly and with all the tools at our disposal?


Aborting a wider debate about growth

Several other valuable discussions in the full mitigation report seem to have left no trace on the Summary for Policymakers. Section 1.6 in chapter 1, “Achieving mitigation in the context of sustainable development,” primarily discusses this in mainstream economic terms (pages 1-38ff.). But it does note the inherent tension between economic development and increased greenhouse emissions. More broadly, it raises the question of whether mainstream economic approaches are fit for purpose in guiding the world to sustainability. For example (page 1-41):

The ‘green economy’ and green growth – growth without undermining ecological systems, partly by gaining economic value from cleaner technologies and systems and [that] is inclusive and equitable in its outcomes – has gained popularity in both developed and developing countries as an approach for harnessing economic growth to address environmental issues. Critics however argue that [the] green economy ultimately emphasises economic growth to the detriment of other important aspects of human welfare such as social justice, and challenge the central idea that it is possible to decouple economic activity and growth (measured as GDP increment) from increasing use of biophysical resources (raw materials, energy). … Literature on degrowth, post growth, and post development questions the sustainability and imperative of more growth especially in already industrialised countries and argues that prosperity and the ‘Good Life’ are not immutably tied to economic growth.

A similar discussion in chapter 1 of the full report, regarding climate ethics, questions the sufficiency of mainstream economic and techno-managerial approaches to mitigation (1-48):

A large body of literature examines the critical role of values, ethics, attitudes, and behaviours as foundational frames for understanding and assessing climate action, sustainable development and societal transformation. Most of this work is offered as a counterpoint or critique to mainstream literature’s focus on safe-guarding of economic growth of nations, corporations and individuals. These perspectives highlight the dominance of economic utilitarianism in western philosophical thought as a key driver for unsustainable consumption and global environmental change. … While acknowledging the role of policy, technology, and finance, the ‘managerialist’ approaches that emphasise ‘technical governance’ and fail to challenge the deeper values that underpin societies may not secure the deep change required to avert dangerous climate change and other environmental challenges.

None of these fundamental economic and ethical debates make it into the Summary for Policymakers. Instead, we find numerous cheery claims that technological innovations and managerial reforms can, by themselves, successfully limit climate change to acceptable levels.

Of course, technical solutions have their place. But so does “moving upstream” and directly addressing the main drivers of climate change: excessive human numbers and overlarge human economies. The science in the Technical Summary and the full AR6 mitigation report fully support doing so. The scientists are calling for a more robust discussion of such fundamental matters and a wider consideration of our mitigation options. But the political apparatchiks who neutered the Summary for Policymakers apparently had other ideas.

It is sad that columnists and editors at The Guardian support such political censorship and willful blindness. And it is ironic, given their supposed sensitivity toward the global poor. For the IPCC’s Sixth Assessment Report makes clear that the poor will bear the brunt of humanity’s failure to adequately mitigate climate change.

Perhaps in the circle of hell reserved for those who undermined effective climate action, Simon Lewis and George Monbiot will rub elbows with Charles Koch and former ExxonMobil CEO Lee Raymond. I know, the very idea is inconceivable to many of my fellow Guardian readers. Just like the idea that there can be too many people.

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21 thoughts on “Population in the IPCC’s new mitigation report

  1. Phil, allow me a simple thought experiment. Imagine that we are able to realise a firm population decline in the developed world. Capital will be shared by less people then, but will still be available and searching for interest on investments. Industry will be looking for new product-market combinations and keep on producing and polluting. With fewer children the labour force will become a greater part of the total population. The number of consumers will decline, but they will have thicker wallets for their luxury goods. True, there are numerous very good reasons for population decline. Especially in the last century population growth was a main driver of increasing GHG-emissions, but to date population degrowth is not an effective fix for climate change. Anyway, it will take too much time. Laws that prohibit investments in GHG-intensive industries may come out as a better solution for climate change.

    1. Jan, I like the idea of prohibiting investments in GHG-intensive industries. Better yet, of direct curbs on them. But as Gaia says, it isn’t either/or, it is both/and.

      The science is clear that human numbers are a key factor in GHG emissions. So past efforts to slow population growth have helped slow growth in emissions. If the world population was still growing at 2% as it was 50 years ago, instead of 1% as it is today, we would have already locked in a 2° C increase in global temperature and be on our way to 3°.

      “iI will take too much time” is a common argument against dealing with population. I think the correct response is, “yes, it will take time, but the benefits will cumulate with time, and fewer people will help address all our environmental problems more effectively.

      1. The kaya identity is a forumla based on multiplication. In other words driving one factor to zero will give zero as a result. The idea of decarbonization is simply striving for bringing carbon intensity to zero. Whether this process will bring a rise of GDP per capita (optimistic outlook of green growth) or not would be irrelevant for the outcome (since it doesn’t matter how big numbers are multiplicated by zero to give zero). Moreover, surely it wolud be easiest way, to bring a factor to zero, because even those who look at population and gdp rise with scare would not welcome bringing those factors to zero (I hope).
        The other, not mentioned aspect here is biodiversity loss, which is interwoven with climate change (it would be probably impossibe to tackle former without the latter). Rise of human population will exert a pressure for land use change (more mouths to feed, more resources needed all products consumed) which also is a contributor to climate change (which is hard to inscribe into the kaya identity).
        What I’m trying to say, is that population growth is contributing to climate change, but curbing that growth is not the soultion that can prevent it happen (not in 8 years period). Jan is right that it will take too long. However, as Phil wrote it is both (or it would be better to say – all four). The fastest way to prevent climate change would be to minimize all four factors bearing in mind that they differ in inertia: results in curbing carbon intensity can be delivered faster than effects of curbing the population. So neither omitting population from climate change preventive measures nor putting it in the centre of climate action sound reasonable to me.

  2. Jan, it’s not either-or, it’s both!
    Also, I suspect, though it’s very hard to prove, that with fewer people a lot of the overconsumption that is possible today wouldn’t be anymore, because it requires a lot of cheap labour. Think fast fashion, holidays, Black Friday… all relying on the poor of the world working for extremely little.

  3. I think you should take on Al Jazeera too! Everytime they discuss food crises, as far as I know, they never even mention population. They talk about everything, like climate change, policies, violence, but that 80 million more mouths to feed every year – a whole large country in a world that is just as big as last year – might be a factor doesn’t even cross their mind.

  4. “Of course, technical solutions have their place. But so does “moving upstream” and directly addressing the main drivers of climate change: excessive human numbers and overlarge human economies.” A SUPER analysis, Phil. Give it all the circulation possible. And thank you for all your effort.

  5. Well done indeed. This is a favourite trick of the Mass Media – lying about what a report has found, in the hope – and indeed firm expectation – that no readers will read the actual source material.
    It no longer annoys me – because it is no longer working. Not because Consumers at any level are starting to run a double check as you did – they will never do that. But because Reality and Truth are starting to make themselves felt, regardless of what lies are spun and what lies are believed.
    In the end Consumption is Consumption. It consumes. If it is at a low level, but by millions, it is just as bad as high Consumption by small numbers of wealthy people. None of it has any future, in the long run.
    Although your hard work will have no effect on events, it has an effect which is worth a lot more but is not measurable – like all things that are priceless and invaluable simply because their value is too vast to quantify.

  6. I concur that this was a SUPER analysis. I am most appreciative that Phil has called out the omission of population concerns in the AR6 Summary for Policymakers and Lewis applauding the omission in his Guardian article. It of course reaches the largest audience and does the greatest disservice. I found only one comment on the article objecting to his dismissal of population concerns.

    1. Thanks Edith and David, I appreciate your appreciation of the blog!

      I wonder whether Lewis realized what was in the full report and covered it up, or whether he just didn’t bother to read further. Either way, it is a poor showing by him and The Guardian.

  7. As a former IPCC focal point for France, I agree totally with this document by Philip Cafaro. In fact, IPCC is an intergovernmental group. As such governments expect that it answers the questions that they ask, not that it answers questions which they do not want to hear about, and they can have some control on that during the discussions on the approval of the Summaries for Policymakers. It seems to me that the consequences of this situation for IPCC Working Groups 1 and 2 are minimal, but that they are very clear concerning WG 3. This is not criticizing the huge amount and the quality of the work made by the contributors to WG3, but if you want to have a comprehensive view you really need to go through the full WG3 report.

    1. Thanks Marc. Do you have any insight into why the AR6 “Summary for Policymakers” would have censored mention of population’s role in this way, when previous summaries did not? It’s interesting that the full report seems to have moved in the other direction, toward greater attention to the costs of growth and greater questioning of the goodness of growth. Maybe this censorship was in reaction to that …?

  8. Thanks for discussion, good feedback, and appreciation of Phil Cafaro’s blog. Please send comment with link to this blog to newspapers and media sites. Also to Guardian – they should see this, and read.

    Frank Götmark, TOP

  9. Hi Philip,
    I do not think that the previous IPCC SPMs contained more information about the influence of population growth on climate change, but I will read them again next week to check that point. I do not think either that WG3 evaluated any mitigation mesure relative to population control. Indeed such mesures do not appear in the data base of mesures studied by the modellers.

    1. Marc, the new IPCC Mitigation Report may not address mitigation measures relative to population control. That would be in line with previous IPCC assessment reports, unfortunately.

      But at least the current Mitigation Report, like previous ones, noted that population growth was a major driver of increased GHG emissions. Past IPCC “Summary” reports have conveyed that information to the public; this one does not. That seems to me an important change.

  10. This isn’t the first time that science (or the truth) has been suppressed for political reasons and nor will it be the last. It’s called propaganda. It brainwashes people. Putin’s invasion of Ukraine is an extreme example of the end product. Scientists and truth-seekers like you and this group have a moral duty to call it out.

  11. It is about time that the role of population growth in global warming was mentioned. The wider ecological crisis is almost entirely due to population growth. I have linked your post at the blog directory writeho dot com (click on the link on my name above). You might link the rest of the articles on this site for a greater audience.

  12. Neither population nor economic growth can’t continue on the finite earth. To save humanity from extinction both economic and population growth must not only cease, both must be reduced. The resources the earth provides humanity are finite and limited. A resource use today is no longer available and cannot use tomorrow. Almost every theoretically renewable resource is being used faster thab nature can replace it and, therefore, must be considered nonrenewable. Every leader of humanity advocating economic growth is a fool and a potential mass murderer. Every person producing more than one child is a fool and a potential mass murderer. It is that simple

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