Cold and high-altitude environments

Extreme environments are places where physical conditions strongly limit human habitation and activity. Temperature alone doesn't determine how extreme a place is. Terrain, water availability and access matter too.

Most cold environments lie at high latitudes. High-altitude environments, by contrast, occur wherever mountains rise sufficiently far above sea level. Several categories overlap in their global distribution:

• Polar environments occupy the high latitudes around the North and South poles. Ice covers much of the Antarctic landmass; the Arctic includes an ocean, sea ice and surrounding northern land areas.
• Glacial areas contain persistent land ice, including glaciers and ice sheets. These occur in Antarctica, Greenland and mountain ranges where snowfall survives successive summers.
• Periglacial areas are cold environments where freezing and thawing strongly shape the ground. They often contain permafrost, ground that remains at or below 0°C for at least two consecutive years. They don't have to lie beside a glacier.
• High mountains in non-polar places include the Andes, Himalayas and East African mountains. As altitude increases, conditions become cold even at low latitudes. Glaciers occur only where temperature and snowfall allow ice to persist.

Hot deserts and semi-arid margins

Aridity is a persistent shortage of moisture caused by low precipitation relative to potential water loss through evaporation and transpiration. Rainfall is very limited and vegetation sparse in Hot deserts. semi-arid areas receive somewhat more rainfall but still experience a substantial moisture deficit. Annual rainfall below about 250 mm is commonly used to identify deserts; roughly 250–500 mm is used for semi-arid areas. Temperature and seasonality also affect this classification.

Many hot deserts lie near 20–30° north and south. Here, descending air inhibits cloud formation and rainfall. Broad concentrations occur across northern Africa and southwestern Asia, southern Africa, interior Australia, and parts of the Americas.

Along some western continental margins, cold ocean currents help keep conditions dry by limiting evaporation and encouraging stable air. Mountain rain shadows also contribute to aridity, as does distance from oceanic moisture sources. Semi-arid regions commonly form transition zones between deserts and wetter grasslands. Their boundaries, though, are irregular rather than continuous belts.

Relief and cold conditions

Relief describes the variation in elevation and slope across a landscape. In high mountains, steep gradients and exposed ridges, together with deeply separated valleys, make movement and construction difficult. Polar environments need not be mountainous. Extensive lowlands or ice-covered plateaus can be extreme because of their climate rather than their steepness.

At high latitudes, solar radiation arrives at a low angle, and daylight varies greatly between seasons. Long winter nights restrict heating. Snow and ice also reflect much of the incoming sunlight. Biological activity and human comfort are limited by low temperatures, strong winds and short growing seasons.

Air temperature generally decreases with altitude in mountains. At high elevations, atmospheric pressure is lower and less oxygen is available per breath. Strong winds affect exposed slopes; snow and ice can obstruct routes. Together, altitude and steep relief create difficulties that many cold lowland areas do not face.

Heat and water shortage

Hot arid environments have little available moisture and high potential evaporation. Under clear skies, intense daytime heating gives way to rapid night-time heat loss, so daily temperature ranges can be large. A hot desert isn't uniformly hot throughout the day or year.

Deserts have varied relief. Rocky plateaus and mountain fronts occur alongside gravel plains and sand dunes. Steep catchments can concentrate runoff quickly, whereas unconsolidated sand can hinder transport and construction. Dunes are only one part of the desert landscape.

Unreliable rainfall and flash floods

Rainfall unreliability refers to variation in when and where rain falls, and in how much falls. A yearly average may hide several dry years followed by a wet one. It may also conceal rain falling in isolated storms that miss neighbouring settlements. Such variation makes dependable water supplies and rain-fed cultivation difficult.

Rainfall intensity is the amount falling per unit of time. Annual rainfall may be very low, yet a short storm can still deliver rain faster than the ground can absorb it. Sparse vegetation intercepts little rainfall. Bare rock or crusted surfaces encourage rapid surface runoff, which steep slopes and narrow channels concentrate.

Low annual rainfall does not, then, mean low flood risk. Flooding depends on storm intensity, infiltration and catchment relief—not just the annual total. Sandy surfaces may absorb substantial water, so rapid runoff is especially associated with rocky, crusted or otherwise poorly infiltrating ground.

How physical conditions become human challenges

People need dependable water and food, shelter and connections to other places to live somewhere. Developing resources also requires workers and equipment, along with energy and transport. Extreme conditions make these needs harder or more expensive to meet—even where valuable resources are present.

• Relief: steep slopes leave less land for building and restrict transport routes. Roads may need tunnels, bridges or long diversions. Unstable slopes can cut off access to settlements and extraction sites.
• Climate: severe cold increases heating costs and shortens the season for outdoor work. Frozen ground makes excavation difficult; when ice-rich permafrost thaws, foundations can become unstable. In hot arid places, scarce water limits domestic supply and farming, as well as water-intensive processing.
• Human discomfort: cold and wind raise the risk of frostbite and hypothermia; heat increases dehydration and heat stress. At high altitude, reduced oxygen availability can impair physical performance. Such conditions affect worker safety and make permanent settlement less attractive.
• Inaccessibility: physical barriers or inadequate transport connections make a place hard to reach. A route may be blocked by ice, steep terrain or shifting sand, even if the destination is nearby.
• Remoteness: long distances from population centres, markets and services mean longer journeys and higher supply costs. Medical assistance may take time to arrive, as may replacement machinery and specialist workers.

Inaccessibility and remoteness can reinforce each other, but they aren't the same. A nearby mountain settlement may be difficult to reach. A distant desert mine, by contrast, may have a reliable road while still lying far from markets.

Effects on settlement and resource development

Settlements tend to cluster in places where local conditions ease the constraints, such as sheltered valleys, dependable water sources or places with transport connections. Even where particular locations support substantial economic activity, large surrounding areas may remain sparsely populated.

Valuable resources don't remove physical difficulties. A mineral deposit can attract investment, yet costly transport and protective buildings can push up extraction costs. Reliable water supplies and restricted working seasons may add to those costs. The same climate can discourage ordinary settlement while allowing a high-value resource operation to continue.

Illustrative examples

The class chooses its own detailed examples. For each one, identify the location and its extreme conditions, then a habitation or resource activity. Explain how those conditions cause practical difficulties rather than simply describing the weather.

Norilsk, northern Russia, illustrates resource development in a cold, remote location. Nickel and copper deposits support a major industrial settlement. Long, severe winters, however, increase heating needs and limit outdoor work. Permafrost makes foundations difficult to build, and there is no road connection to Russia’s main road network. Supplies therefore depend on air transport and shipping connections through Dudinka.

Coober Pedy, South Australia, illustrates habitation linked to opal extraction in a hot arid interior. Living on the surface is demanding because of summer heat and scarce water. Distance from major cities also raises supply and service costs. Underground homes reduce exposure to outside temperature extremes, but the settlement still faces water and remoteness constraints.

Glacier advance and retreat

As climate changes, so does the distribution of extreme environments. Over long periods, colder conditions can extend glaciers and cold-ground environments into lower latitudes or lower elevations. Warming can shrink their extent, though the response depends on local snowfall and altitude, as well as how long the ice takes to adjust.

A glacier’s mass balance is the difference between the ice it gains through accumulation and the ice it loses through ablation. Snowfall supplies most of the mass added through Accumulation. Ablation removes mass through processes such as melting, sublimation and the loss of icebergs.

If accumulation exceeds ablation for a sustained period, a glacier gains mass and may thicken and advance. If ablation exceeds accumulation, the glacier loses mass and its terminus may retreat. Cooler summers can reduce melting; increased snowfall can add to accumulation. Warming or reduced snowfall can favour retreat.

Land ice covered much larger areas during past glacial periods than it does today. Subsequent warming reduced its extent. Many mountain glaciers are now retreating, but they aren't all changing in the same way. Local differences in snowfall and shading, along with glacier dynamics, affect the response.

Natural desertification

Natural desertification describes the development or intensification of desert-like conditions through natural environmental change. The change in moisture availability and vegetation must be lasting, rather than limited to a single dry season.

The boundary between semi-arid land and desert can shift when rainfall persistently declines, atmospheric circulation changes or evaporative demand increases. Less moisture limits plant growth. As vegetation declines, more ground becomes exposed to wind erosion; infiltration can also decrease where surface crusts develop. These feedbacks can reinforce drying.

Desert margins don't move as a uniform front. Local relief and soils, together with water availability, create an uneven pattern of change. During wetter periods, vegetation can recover and desert-like conditions can contract. Boundaries can therefore fluctuate over decades as well as shift over millennia.

The Sahara’s mid-Holocene transition illustrates natural change over a long timescale. Several thousand years ago, stronger monsoon rainfall supported lakes and more extensive vegetation across parts of what is now desert. Changes in Earth’s orbital configuration altered seasonal heating and helped weaken the monsoon. Vegetation–climate feedbacks reinforced the transition towards greater aridity. Today’s desert distribution is therefore not a permanent feature of the planet.