Global population has grown almost continuously for centuries, and popular imagination often still assumes that growth simply continues indefinitely. Most current demographic projections instead expect global population to peak at some point this century and then begin a sustained decline, a genuinely significant projected turning point driven primarily by falling fertility rates spreading to an increasing share of the world's population, following a pattern already well underway in many individual countries.
Falling fertility, not rising mortality, is driving the projected peak
The projected global population peak isn't driven by rising death rates; it's driven by falling birth rates spreading progressively to more of the world's population, as more countries complete a well-documented pattern demographers call the demographic transition, in which fertility rates decline substantially as a country develops economically and socially. Once a large enough share of the global population lives in countries with fertility rates at or below the replacement level, the level needed for a population to remain stable without immigration, global population growth necessarily slows and eventually reverses, even though death rates themselves aren't rising — it's a mathematical consequence of enough of the world's population simply having fewer children per generation than immediately preceding generations did.
Different demographic models still disagree meaningfully on timing
Exactly when global population is projected to peak, and how steep the subsequent decline is projected to be, varies meaningfully across different demographic models and organisations, since the ultimate outcome depends heavily on assumptions about how quickly fertility rates in currently higher-fertility regions will continue to fall, assumptions different demographic research groups make somewhat differently based on their own specific modelling approaches. Some projections place the global peak around the middle of this century, while others project it somewhat later, and the projected size of the population decline that follows likewise varies meaningfully between different models — a genuine, ongoing source of disagreement among demographers, even though there's now broad consensus across essentially all major demographic models that some kind of global peak followed by decline is coming this century, not simply continued indefinite growth.
What we're still unsure about
The broad demographic consensus that global population growth is slowing and a peak is likely this century, driven by spreading fertility decline, is well supported and widely documented across major demographic research organisations. What remains genuinely unsettled is the specific timing and scale of that peak and subsequent decline, since these depend heavily on how fertility trends in currently higher-fertility regions of the world actually evolve over coming decades — a genuinely uncertain, forward-looking question that different research organisations model somewhat differently, producing meaningfully different specific numerical projections even while broadly agreeing on the overall directional trend.
This sits inside Global Population Trends & Projections, one of seven topics in Demographics, one of four domains in Sociology, one of seventeen subjects the app can quiz you on.