For over two centuries, the spectre of overpopulation has haunted global debates about food security, sustainability and the environment. All the way back in 1798, English economist and scholar Thomas Robert Malthus wrote his influential piece, An Essay on the Principle of Population, arguing that the human population will always grow faster than our ability to produce food, eventually overwhelming the planet’s available natural resources. The catastrophe Malthus prophesied has yet to arrive, thanks to technological advances and human ingenuity. But the ideas of Malthus and his 20th century successors such as Paul and Anne Erlich—authors of the 1968 treatise The Population Bomb—still inform much of the conventional wisdom around the relationship between population growth and the climate crisis.

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For over two centuries, the spectre of overpopulation has haunted global debates about food security, sustainability and the environment. All the way back in 1798, English economist and scholar Thomas Robert Malthus wrote his influential piece, An Essay on the Principle of Population, arguing that the human population will always grow faster than our ability to produce food, eventually overwhelming the planet’s available natural resources. The catastrophe Malthus prophesied has yet to arrive, thanks to technological advances and human ingenuity. But the ideas of Malthus and his 20th century successors such as Paul and Anne Erlich—authors of the 1968 treatise The Population Bomb—still inform much of the conventional wisdom around the relationship between population growth and the climate crisis.

All else being equal, the argument goes, fewer people means fewer mouths to feed, less demand on our limited natural resources, and crucially, fewer emissions. In this context, the news that we’re in the middle of an unprecedented collapse of the global birth rate should be cause for celebration. The UN estimates that the world’s population will peak at about 10.4 billion people in the 2080s, and remain at that level until 2100. Another set of projections, published by the University of Washington’s Institute for Health Metrics and Evaluation (IHME) in 2020, estimates that the global population might peak by 2064 (at 9.73 billion), followed by a steady decline that will bring us to 6 billion by 2100. That’s approximately the same number of people as were alive in 2000.

This is certainly good news, particularly for food security and poverty alleviation. But when it comes to the fight against climate change, the case for optimism is much weaker. The first problem is the timeline. Even if we go by IHME’s more aggressive projections, the human population isn’t shrinking nearly fast enough to prevent the climate crisis. A smaller population in 2100 won’t reduce carbon emissions today, and any changes will come long after the mid-century deadline for zero emissions that we need to meet to avoid climate disaster.

A 2023 study by researchers at the University of Texas in Austin makes a convincing case that “contemporaneous fertility rates are, essentially, quantitatively irrelevant to our climate future.” According to the study’s findings, the difference in long-run temperature rise between population stabilisation and the UN’s population decline scenarios, over the next two centuries—given our current climate policies—is very small (4.22°C vs 4.27°C by 2200 respectively).

In addition, the relationship between population and emissions numbers is far from linear. Two of the world’s largest sources of greenhouse emissions—the US and China—both have fertility rates below replacement levels. Meanwhile India, with its growing population, still counts for 1/8th the amount of per capita emissions that the US does. Affluence, technology and policy all have a much greater impact on climate mitigation than the number of people on the planet.

“Globally, the top 1% of the population by income, emits about 101 tonnes of CO2 equivalent per year on a per capita basis, while the bottom 50% emits 1.4 tonnes,” says Avantika Goswami, a climate policy researcher at the Centre for Science and Environment. “Private jets and the growing use of SUVs are some of the biggest contributors to emissions of the rich, which large sections of the population in the Global South do not have access to.”

In fact, a 2023 article published by London’s Centre for Economic Policy Research (CEPR) argues that a declining population may actually hinder attempts at fighting climate change by increasing resource scarcity. Given our current economic model, their counter-intuitive argument goes, a declining population means more ageing, non-productive dependents and less labour available for research and development, leading to greater reliance on resource-dependent production, especially in agriculture.

Whether or not you agree with that idea—and many don’t—the consensus seems to be that population numbers are a lot less relevant to the climate change fight than other factors, such as intergovernmental cooperation, managing global conflict, technological investment, and low carbon development policies. This doesn’t mean, of course, that population numbers are entirely irrelevant.

“When it comes to climate change, population matters tremendously because demand will increase from coal, to food to roads,” says Mridula Ramesh, founder of the Sundaram Climate Institute and author of The Climate Solution – India’s Climate Change Crisis and What We Can Do About It. “This demand has to be met with supply which causes emissions, resource depletion, pressure on forests etc.”

But, as Ramesh argues, the more important factor is how we choose to meet that demand. “Rather than population per se, it is about how one meets the increased demand—how efficiently one makes stuff, how much recycled content goes in, and how one respects the environment in making the stuff.”

“It’s a spectrum. The optimistic point of view is that [population] doesn’t matter at all. The pessimistic point of view is that we’re doomed. I think the truth lies somewhere in the middle, probably closer to the optimist perspective.”