Only low-population growth can keep warming below 2 degrees

Professor Ian Lowe – emeritus professor of science, technology and society at Griffith University, former President of the Australian Conservation Foundation (ACF), and author of the excellent book Bigger or Better?: Australia’s Population Debate – is lead author of a new discussion paper entitled Population and Climate Change.

The report explores questions including:

  • How is population a key driver of climate change?
  • How has population growth contributed to Australia’s greenhouse gas emissions?
  • What are the implications of population growth for climate change mitigation and adaptation in poorer countries, compared to the more affluent countries?
  • How does the greenhouse gas impact of having fewer children compare with other climate-friendly actions such as eating less meat or avoiding air travel?
  • How can population policy be used as part of the actions to avoid catastrophic climate change?
  • How will climate change affect the health, safety and growth of populations?
  • Why has population been so often ignored in the policy prescriptions for combatting climate change?

Below are the reports key points:

  1. Human activities are releasing greenhouse gases and causing climate change. The quantity of greenhouse gases is the product of emissions per person multiplied by the population. Hence climate change can’t be ‘blamed’ on either consumption patterns or population but both together: each multiplies the other and both must be part of action to avoid catastrophic outcomes.
  2. Population growth increases people’s vulnerability to climate change in many ways. Globally, water and food insecurity are already increasing due to population pressure. More people mean more housing vulnerable to floods, bushfires and storm damage; rapid growth leads to inadequate infrastructure; larger and denser cities raise the urban heat island effect and increase disease transmission.
  3. The future challenges of climate change, including emissions reduction and adaptation, can be lessened by minimising further population growth. In developed countries like Australia, having fewer children is the most impactful lifestyle choice available to individuals to lessen their environmental impact. High immigration also increases emissions, since most migrants to Australia shift to more carbon-intensive lifestyles.
  4. High population growth in low-income countries can cause environmental impacts such as deforestation and soil degradation. These not only accelerate climate change by reducing carbon stores in forests and soils, but also reduce the capacity of the local food production system to adapt to the changing climate. Lower population growth in low income countries will help increase their standard of living, while minimising the growth of total emissions as their per capita emissions rise.
  5. In high-fertility countries, voluntary family planning services are severely underfunded and under-promoted, leaving many women without the means to avoid pregnancies they don’t want. Providing these services, empowering women and promoting small families would have multiple benefits for communities coping with climate change. Family planning programs are a ‘best buy’ for development, environment and climate adaptation.
  6. Climate mitigation models show that sufficient emissions reduction cannot be achieved unless the model scenarios assume a rapid peak and decline in global population. Population stabilisation alone can’t solve climate change, but ignoring population will ensure we fail.

And below is the Summary alongside key charts:

The relationship between population and climate change is complex. At a basic level, for a given lifestyle (consumption pattern), emissions of the greenhouse gases that cause climate change are directly proportional to the size of the population. For example, if Australia’s recent population growth rate of about 1.5% per year were to continue, in less than 50 years we would double our demands for energy, food, water and all natural resources. All else being equal, we would double our carbon footprint also. On the other hand, in a hypothetical world where we achieve lifestyles entirely free from greenhouse gas generation, how many of us there were would make no difference to the climate. But even if this were achievable, which is questionable, we could decarbonise our lifestyles more rapidly if population growth was not constantly adding to the demand for energy and resources. Hence, the rate of population growth will make a considerable difference to the cumulative emissions generated during the transition. Furthermore, population growth greatly increases our vulnerability to the impacts of climate change.

The population issue has had a controversial history which has led to the development of a ‘taboo’ against talking about population as a policy-relevant factor. This paper calls for a new level of maturity in discussing the population issue. It should no longer be acceptable for unfounded accusations of racism to be used to silence respectful and thoughtful discussions about population growth. It should no longer be acceptable – at an epochal moment of existential risk for human civilisation – for climate policy prescriptions to conspicuously exclude population-related actions in the face of abundant evidence (as reported in this paper) that such measures are feasible, effective and consistent with human rights and democratic values. Ending global population growth more swiftly and at a lower peak is a necessary but not sufficient condition for overcoming the climate crisis.

Population and consumption work together

The Intergovernmental Panel on Climate Change (IPCC) says ‘Globally, economic and population growth continue to be the most important drivers of increases in CO2 emissions from fossil fuel combustion.’ But these are not independent contributors to emissions; they multiply each other. Most emissions are attributable to the richest billion people, but their economic growth since 1970 has not increased their average emissions per person. The growth in emissions has come from lifting multitudes of poor people to a modest middle-class lifestyle in places like China and India.

It is futile to ‘blame’ past emissions on either population or consumption patterns when they are the product of both. What should be of more interest to us is the extent to which the future challenges of climate change, including emissions reduction and adaptation, can be lessened by giving due attention to population growth. This paper argues that our climate change response can’t afford to ignore the potential to minimise further population growth.

Slow-response actions are no less urgent

Nobody expects addressing population growth alone to solve climate change. There is no intention to deflect attention from high emissions consumption patterns, nor to blame the poor for the excesses of the rich. Demographic inertia means that even concerted efforts to slow population growth are unlikely to have significant impact on the timescale demanded by the climate crisis. Measures to decarbonise our energy system and reverse the loss of vegetation and biodiversity are needed urgently in this decade, if we are to avoid catastrophic impacts of climate change. Measures to reduce childbirth will take decades to make an appreciable difference to greenhouse gas emissions and human demands on nature.

Nevertheless, how well we do in the second half of this century will depend more on what we do about population growth this decade than on any actions that will remain available to us in 2050. If the successful efforts to promote voluntary family planning adoption in the 1970s and ’80s had not been abandoned in the 1990s, the global population might now be on track to peak below 9 billion. Because of decisions made in the 1990s, we’re heading for 11 billion or more. But if we renew family planning efforts now, a peak below 10 billion is possible and we could end this century with fewer than 8 billion people. If we wait until 2050, 11+ billion would be locked in.

A slow fruition does not make population action any less urgent. As the proverb says, ‘The best time to plant a tree is 20 years ago. The second-best time is now.’ So it is with addressing global population. The climate crisis is largely a product of the shortsightedness of political responses decades ago. Those who say that reducing birthrates is too slow to be relevant to the climate change response are suffering the same shortsightedness that created the problem they seek to fix.

In rich countries, fewer people means lower emissions and fewer vulnerabilities

Any increase of population in the more affluent countries will add to those countries’ use of resources and their greenhouse gas emissions. In a rich country, having fewer children does more to slow climate change than any of the other actions often advocated, such as eating less meat, avoiding air travel or using only renewable energy. If immigration is high enough to cause population growth, it also increases a country’s emissions, but some people argue that it makes no difference globally. This is untrue: the average migrant to Australia increases their carbon footprint fourfold by adopting Australian lifestyles. While Australians have recently reduced their per capita emissions a little, Australia’s total emissions from energy have risen 49% since 1990 due entirely to population growth of 8.3 million people.

Australia is not only one of the world’s largest per capita emitters of greenhouse gases, it is also among the countries likely to be most affected, in terms of negative impacts on agriculture, water supply, bushfire threat and extreme weather events. All these threats are intensified by the threat-multiplier of population growth.

The current Australian government policy of encouraging high levels of migration could see the 2060 population approaching 40 million and continuing to grow rapidly. That scale of increase would significantly magnify the task of producing enough clean energy to meet our material needs within a responsible carbon budget. Australian agriculture is unlikely to feed that number during increasingly frequent and severe droughts, and water security will depend on costly and energy-intensive desalination or recycling. These serious vulnerabilities are entirely avoidable if we choose population stabilisation.

In poor countries, smaller families are essential for adaptation

Population growth heightens vulnerability to climate change to a much greater extent in poor, high-fertility countries. For most of these countries, population growth itself is a greater threat to security and wellbeing than climate change is. Saying this does not in any way diminish the serious impacts of climate change. However, if a projected 11–25% reduction in crop yields this century due to climate change is considered a crisis, it is absurd to claim, as many people do, that population growth in high-fertility countries is not important when it will diminish the available water and agricultural land per person by a factor of three or more, while ensuring high levels of unemployment and poor infrastructure provision. While family size should be considered part of emissions reduction efforts in rich countries, it should be integral to adaptation efforts in poor countries. Nevertheless, the emissions caused by growing numbers of the poor are not insignificant. Deforestation is particularly vulnerable to population pressure.

Currently, family planning services are badly underfunded, denying many women access to safe and reliable contraception. As a result, the fall in birthrates has been much slower than was anticipated a generation ago, unemployment is rampant and hunger is once more on the rise.

Many of the beneficial impacts of lower birthrates are enjoyed much more rapidly than their effect on carbon emissions. These benefits include greater autonomy of women, health of infants, food security of families, protection of biodiversity, employment prospects for youth and economic development of nations. If climate adaptation is dominating the agenda for international aid, it makes sense that family planning should be included as an adaptation measure.

Climate change will affect world population

The other side of the coin is the impact climate change is projected to have on population, through greater loss of life. The frequency of extreme heat events, floods and crop-destroying droughts is projected to increase substantially. Some Pacific islands and low-lying coastal areas will become uninhabitable, causing either loss of life or relocation of whole populations. Mass migrations could possibly in turn lead to conflict between the displaced people and those whose traditional lands they enter. However, responses to climate change can have some beneficial health impacts. Urban air pollution and indoor smoke exposure are both major causes of premature deaths, and might be substantially reduced by electrification of energy systems. It is difficult to anticipate the net effect on population trends.

Only low-population scenarios can keep warming below 2oC

The most compelling reason to include population in the climate change response is that climate mitigation models are only able to achieve sufficient emissions reduction if their scenarios assume a rapid peak and decline in global population. These assumptions are not readily visible: they are hidden under the labelling of scenarios such as ‘SSP1’ or ‘SSP2’. Without making these assumptions explicit, and discussing the actions that could help achieve the required birth reductions in a way that elevates people’s rights and freedoms, these scenarios can’t become reality.

Addressing population growth alone can’t solve climate change, but not addressing it will ensure we fail.

I have regularly argued that Australia’s goal of achieving its “net zero” emissions obligations by 2050 is a pipe dream given it plans to lift Australia’s population by 13.1 million people (50%) over the next 40 years via mass immigration of 235,000 people a year:

Australia’s immigration policy should be established on the principle that we want to stabilise the population at a level that would be sustainably supported. This doesn’t mean pulling up the drawbridge, but it does mean much lower levels of immigration than are currently planned.

Ultimately, Australia can only control what happens within its own borders. And growing the population so fast via mass immigration is within our direct policy control and unambiguously negative for Australia’s environment, water security, liveability, housing affordability, as well as meeting our emissions reduction targets.

Environmental groups need to stop the hypocrisy and confront Australia’s population addiction head on, since it is a direct driver of our environmental malaise.

Unconventional Economist


  1. I watched Soylent Green on Netflix the other day. Great movie set in the year 2022, 48 years into the future.

    The world was an environmental disaster, an economic disaster, a social disaster, and the primary cause of all of this was overpopulation.

    Since then there have been a lot of dystopian futuristic/ post-apocolyptic movies made, but none of them really have overpopulation as the root cause of the disaster. Overpopulation is just a “sacred cow” topic that we’re not allowed to touch. Too controversial.

    • Fantastic movie. Unfortunately both sides of politics love population increase due to the many reasons always stated on this site. It’s a world wide issue but don’t worry EVs will save us /s

      • Avengers series is all about population issues across the universe. Sometimes I think to myself, Thanos is probably right.

        • At first I thought he was a c*nt for killing half the population but then I thought about it some more and realised he was right.

          • So… You’ve got control of a magical item that can do anything, and the only thing you can think of is to kill half of everything in the universe ? Not even take a slight step back and make, say, 2/3 of every living thing in the universe infertile ?

          • So you actually spent time responding to my throw away comment on a fictional movie and that’s the best solution you can come up with?

          • No. But I’m not going to spend a lot of time on a throw away comment about a fictional movie, am I ? 🙂

            (There is actually a semi-serious point here, that if the best solution to “overpopulation” you can come up with is to kill a bunch of people, then you probably shouldn’t be allowed anywhere near the decision-making process.)

          • Using a quote from another movie The Day the Earth Stood Still, ‘But it is only on the brink that people find will to change. Only at the precipice do we evolve’.

            Our politicians and by default the people of the West are gambling that technology will save us by reducing our carbon footprint. Any meaningful change to our lifestyles, reduced airplane travel, reduced car travel, one child policy, big taxes on waste, nuclear power are all impossible policies to make meaningful change. All we do is make virtual signal changes like substituting plastic straws for paper and say job well done.

            No one wants to take decisive action because as individuals we believe we will easily survive any changes in the climate. However, our supply chains are so complicated if they collapse food shortages arise and then things get very interesting. Sure we are a small population but we have 0 fuel reserves and can’t make the fertilizer to grow enough food to feed ourselves. This goes for almost everything we use to maintain our middle class lifestyle.

            So, my conclusion, get yourself into the 0.1% cohort, the middle class will disappear in the next few decades because they can’t make the hard decisions now. Goodbye middle Australia welcome the new feudal system where you are either a slave or a master.

      • kierans777MEMBER

        I remember trying to use that movie as an example to help a friend understand where we’re headed if we don’t tackle the population issue. At the time he wasn’t convinced but has changed his mind and reminded me of that conversation recently.

    • The problem is that the most effective (at least, within reasonable bounds of ethical and moral behaviour) way to reduce population growth is to make the poorest people in the world richer, which comes with one major downside from the perspective of everyone else: as they get richer, they consume more.

      • Easy solution to reduce population.

        Use the same process that applies to rezoning permission in Sydney. Make it as hard to get permission for an extra baby as it is to get permission for an extra dwelling in Sydney.

        What happens if you build an extra dwelling without permission in Sydney? It gets demolished.

        We can’t really demolish babies born without permission, so we would have to confiscate them from the parents and then mandate a special vaccine (eg sterilising) for the sinful baby developers.

        Just imagine the wealth produced by this process.
        “Oh we are saving up for a deposit on permission for a baby”
        “I’ve just borrowed 1.4 and got conditional approval for a baby girl”
        “I made a great investment. Bought baby permission in 2022, Hubby died in 2024 and I just sold for a 80% capital gain!”

        By applying a baby permission “zoning” scheme we would soon be as successful in forcing small families onto people as we now are on forcing small home units onto familes in Sydney. And the beauty of the scheme is that the morons would not even understand what was happening. They would just blame high prices and blame themselves for not buying earlier.

        “Look at these high prices of babies” they would say “@#$% I wonder what causes that”.

  2. I am confident that Australia will stick with the existing LibLab proposal, aka the Australian Way, or 1788 Forever.

    That is, the best way to Net Zero is to hike our population by 40%, prolong the gas and coal fields, go long on land clearing and habitat destruction, kill all the koalas, and splurge all the water. I mean, what could possibly go wrong?

  3. The cause of Climate Catastrophe is over population.
    The cure for over population is Climate Catastrophe.

    And it is here now. By 2050 CC will be beyond any meaningful action, it may well be too late already.
    We continue to have our cake and eat it too, burn the candle at both ends, and increase our emissions at record levels.and expect everything will be OK.

    This is just a small part of what is going wrong.

  4. kierans777MEMBER

    Hence climate change can’t be ‘blamed’ on either consumption patterns or population but both together: each multiplies the other and both must be part of action to avoid catastrophic outcomes.

    Well put. To paraphrase the taco girl “it’s both”.

    • It should be plainly obvious that while both are relevant in an abstract sense, consumption must take precedence from a mitigation perspective, as it is both a) the variable that can be meaningfully changed on a useful timescale and b) politically easier.

  5. “In a rich country, having fewer children does more to slow climate change than any of the other actions often advocated,”

    Absolutely an utterly false and genocidal statement. Every birth not created by the local population, is replaced by a birth from the developing world transferred to the first world via immigration.

    All that occurs, net, from the first world reducing its own birthrates, below replacement, is their replacement in their own nations. There is no net reduction in carbon emissions from first world reductions in births.

  6. David WilsonMEMBER

    A few facts will debunk this drivel.
    1. As all intelligent people know population reproduction rates are falling around the world .. think, China, USA, Europe etc so population will likely start to reduce in the next twenty years or so as reproduction rates also fall in Africa, India and South America.
    2. Our BOM said earlier this year that 2021 was Australia,s 19 th warmest year.
    3. The IPCC, NASA, etc confirmed 2021 as our sixth warmest year
    I get very concerned about disinformation by so called scholars that continue to ignore these known facts and that climate change is and will remain a natural phenomenon as has been the case since the beginning of time.
    All we need to do is stop pollution of of seas, waterways and air being also careful that chemicals don’t destroy our soil structures.

    • 1. As all intelligent people know population reproduction rates are falling around the world .. think, China, USA, Europe etc so population will likely start to reduce in the next twenty years or so as reproduction rates also fall in Africa, India and South America.

      Peak world population isn’t likely to happen for fifty years. Reproduction rates are falling, but still above replacement in many countries.

      2. Our BOM said earlier this year that 2021 was Australia,s 19 th warmest year.

      How many of the next 18 happened in the last 25 years ?

      3. The IPCC, NASA, etc confirmed 2021 as our sixth warmest year

      How many of the next 5 happened in the last 10 years ?

  7. The earths temperature in the last 4 years is 0.67 C lower. Meanwhile gates etc were funding Harvard putting up high atmospheric shields of chemicals…Don’t know if that one is still on, an earlier one is not. Volcanoes are spewing particles high up, the last, near Tonga was very very high and will affect a band from above Sydney right thru queensland, reducing sunlight and affecting crop yields this year. Hits Africa and just another horror for them. Estimate was just this year, not sure on that at all.
    Plants need carbon dioxide it’s already at a very low level, we could do with more. The planet is cooler than a thousand years ago. Last thing i want is to go into a cyclical sun cooling like the Maunder Minimum ..a lot of people died, or that in the 1300C or so when parisians lived in the sewers and wolves prowled the streets, and to find the planet cooled enough to keep getting colder for 200 years. That’s the paranoid dream applied to children’s children..

    China has records back 5000 years and is buying in grain, buying land across North Africa which was the fertile area 1500 years ago. And in Aus in sun cooling we get cold seas so drought. Hard to find information re past in Aus, goog has a stranglehold on climate aka global warming, but duckduckgo gives a couple of pages of Aus records from colonials writings. In Vic the Great Forest area was an ark.

  8. “:Family planning programs are a ‘best buy’ for development, environment and climate adaptation.” > Donate generously