The relationship between population and climate change is often oversimplified. Yes, more people generally means more greenhouse gas emissions. But the correlation is far from linear. The average American emits 15 tons of CO2 per year; the average Indian, 2; the average Nigerian, less than 1. A child born in the United States contributes as much emissions as 7 born in India.

This means population growth in high-emitting countries has a vastly greater climate impact than growth in low-emitting ones. If the world's population stabilized tomorrow but consumption patterns did not change, emissions would still be far too high. Conversely, the billions added by 2050 — mostly in Africa and South Asia — will add relatively little to global emissions unless their economies industrialize on fossil fuels.

The key variable is not how many people, but how they live. A world of 10 billion people using renewable energy and plant-based diets would emit less than a world of 5 billion living like the average American today. Technology and policy, not just population size, will determine the climate outcome.

That said, population does matter. The UN estimates that achieving lower fertility through education and access to contraception could reduce the 2100 population by a billion or more, with corresponding emissions savings. This is one of the few climate interventions that also improves health, education, and gender equity.

Climate change also affects population. Rising sea levels, droughts, and extreme weather displace people — the World Bank estimates that 216 million people could be internally displaced by 2050 due to climate. This creates migration pressures that reshape populations in both origin and destination countries, adding a new dimension to demographic change.