Mountains occupy a much larger share of the planet than their individual peaks and ranges might suggest.

According to the 2025 United Nations World Water Development Report, published by UNESCO on behalf of UN-Water, mountain regions cover around 33 million square kilometers, equal to 24% of the global land surface excluding Antarctica.

That area includes far more than the world's highest ranges. Mountain regions extend across every inhabited continent and encompass landscapes that vary widely in elevation, climate, vegetation, and human settlement.

Their significance also extends well beyond the land they occupy. Mountains are an important part of the global water cycle, support agriculture and energy production, provide habitat for diverse ecosystems, and are home to more than a billion people.

Defining a mountain globally is more complicated than simply setting a minimum elevation. A high plateau can sit thousands of meters above sea level while remaining relatively flat, while rugged terrain can be mountainous at much lower elevations.

The 24% figure reported by UNESCO is based on an estimate cited to a 2020 study by researchers at the Food and Agriculture Organization of the United Nations and its partners. The underlying methodology uses the United Nations Environment Programme World Conservation Monitoring Centre classification of mountain areas.

That classification considers several physical characteristics, including elevation, slope, and local differences in elevation. Land at very high elevations can qualify based on elevation alone, while lower terrain generally needs to meet additional criteria related to steepness or ruggedness. The classification also includes certain small interior areas surrounded by mountains.

Using this geographic framework and excluding Antarctica, UNESCO reports that mountain regions account for around 33 million square kilometers, or almost one-quarter of the world's land surface.

The importance of mountains becomes clearer when their influence on freshwater is considered.

Mountains typically receive more precipitation than surrounding lowlands and can store water as snow and ice during colder periods. As snow and glaciers melt, that water feeds streams and rivers that can travel far beyond mountain regions.

UNESCO estimates that mountains provide 55% to 60% of global annual freshwater flows. The contribution varies considerably by location, ranging from about 40% to more than 90% in different parts of the world.

Some major rivers are especially dependent on mountain water. UNESCO's report identifies the Amu Darya, Colorado, Nile, Orange, and Rio Negro among rivers where mountain sources contribute more than 90% of mean annual flow. The Euphrates, Indus, São Francisco, Senegal, and Tigris receive more than 70% of their flows from mountain waters.

This connection means the economic importance of mountains does not end where mountainous terrain gives way to lowlands. Water originating in mountains supports households, farms, power generation, businesses, and ecosystems downstream.

Agriculture provides one of the clearest examples of this wider dependence.

The UN World Water Development Report says that up to two-thirds of irrigated agriculture globally may depend on mountain waters. This is an estimated dependency rather than a measurement of the share of all agricultural water physically originating in mountains.

Mountain water is particularly important where snow and ice act as seasonal stores. Water accumulated during colder months can be released later in the year, helping supply river systems during warmer periods when agricultural demand can be high.

UNESCO also reports that around 2 billion people depend on mountain waters. Its detailed facts and figures explain that this widely cited number is derived from an estimate that about 2 billion people live in drainage basins originating in mountains.

Mountain waters also support economic activity through sectors including agriculture, energy, tourism, forestry, and water-reliant industries. UNESCO notes that the benefits therefore extend from people living in mountain communities to much larger populations and economies downstream.

Mountains are sometimes perceived as sparsely populated wilderness, but they are also home to large human populations.

According to the UN report, about 1.1 billion people lived in mountain regions in 2015, representing roughly 15% of the world's population at the time. That was nearly double the slightly more than 575 million people estimated to have lived in mountain regions in 1975.

The 2015 figure also shows how varied mountain settlement can be. Around 34% of the mountain population lived in cities with more than 50,000 people, 31% lived in towns and semi-dense areas, and 35% lived in rural areas.

Agriculture and pastoralism remain important sources of livelihoods in rural mountain regions, although the terrain can impose significant constraints. UNESCO reports that an estimated 45% of the world's mountain areas are unsuitable or only marginally suitable for crops, pastoralism, or forestry. Higher elevations can bring colder temperatures, shallower soils, smaller areas suitable for cultivation, and greater difficulty using agricultural machinery.

Mountain communities have adapted to these conditions through practices including terrace farming, livestock production, and local water-harvesting systems.

The enormous geographic area occupied by mountains also contains a wide range of ecosystems.

Temperature and precipitation can change substantially with elevation, allowing forests, grasslands, alpine tundra, glaciers, and other environments to exist within mountain systems.

According to the UN World Water Development Report, mountain regions contain 25 of the world's 34 biodiversity hotspots. Forests cover approximately 40% of global mountain areas.

Those forests perform functions that extend beyond providing wildlife habitat. They can help stabilize steep slopes, regulate groundwater flows, reduce surface runoff and soil erosion, and lower the potential for landslides and flooding.

The combination of elevation, climate, water availability, and varied terrain therefore makes mountains important not only for the amount of land they occupy, but also for the concentration of ecosystems they contain.

Mountain environments are also particularly sensitive to changes in temperature.

UNESCO reports that global warming is reducing snow accumulation and the duration of snow cover, accelerating glacier loss, increasing permafrost thaw, and contributing to changes in rainfall and mountain hazards.

Most mountain glaciers around the world are thinning rapidly, according to the 2025 UN report. Under scenarios in which global warming reaches between 1.5°C and 4°C, mountain glaciers are projected to lose 26% to 41% of their total 2015 mass by 2100. This is a model-based projection across a range of warming levels, not a reported loss that has already occurred.

Changes in snow and glaciers can also change when water reaches downstream users. Initially, increased melting can raise runoff from some glacier-fed basins. As glacier mass continues to decline, however, a point known as peak water can be reached, after which meltwater runoff decreases. UNESCO says there is strong evidence that peak water has already passed in glacier-fed rivers in the Swiss Alps, western Canada, and the Tropical Andes.

That matters for communities, agriculture, and industries that rely on predictable seasonal flows.

The statistic at the center of the picture is striking on its own. Mountain regions cover around 33 million square kilometers, or 24% of the global land surface excluding Antarctica, according to UNESCO.

But their significance is greater than their geographic footprint suggests.

Mountains supply a substantial share of global freshwater flows, contribute water to major river systems, support agriculture and other economic activity, contain important ecosystems, and provide homes and livelihoods for more than a billion people.

Their influence also travels downhill. Rivers originating in mountain regions connect high-altitude landscapes with farms, cities, industries, and ecosystems far beyond them.

Mountains occupy nearly one-quarter of the world's land under UNESCO's reported measure, while the water and ecosystems they support reach much farther.