Pollution, climate change, and poverty are not separate crises. They are a single compound system driving survivability risk, which suppresses human reproduction, which produces multi-century population collapse — concentrated in the very regions experiencing the fastest demographic growth.
Survivability risk is not about mortality alone. Chronic PM2.5 exposure reduces fertility. Heat stress raises miscarriage risk and reduces labor productivity. Water contamination triggers disease cascades. Economic precarity delays family formation indefinitely. These pressures compound — and they are concentrated in the regions adding the most people.
Global fertility has fallen from 5.0 (1960) to 2.27 (2023). Over 70 countries are now below replacement (2.1). The trend is accelerating: South Korea hit 0.72; China dropped below 1.0; India slipped below 2.1. Even Sub-Saharan Africa's fertility is declining faster than any model predicted. The question is not whether global fertility falls below replacement — it is how low it stabilizes, and when.
If below-replacement fertility stabilizes globally around 1.5 — as current trends suggest — the math is relentless. Each generation is roughly 25% smaller than the last. By 2300, global population falls to 7.5–8 billion. By 2500, 4.5–5 billion. By 3000, potentially 1.2–1.6 billion — back to early 19th-century levels, unless fertility meaningfully rebounds.
The regions projected to add 2+ billion people by 2050 — Sub-Saharan Africa, South Asia, parts of Southeast Asia — are the same regions turning red on every survivability metric. More people arriving into zones of rising heat, failing water systems, and degraded air quality is not a demographic dividend; it is a compound vulnerability multiplier.