Mission 1: Antarctica is covered in ice, yet it counts as a desert. How?

Two kinds of extreme environment

• Cold and high-altitude: polar areas, glacial and periglacial areas, and high mountains in non-polar latitudes.
• Hot, arid: hot deserts and semi-arid areas.
• Glacial ice covers about 10% of Earth's land today.
• Drylands cover about 46% of the global land area (IPCC, low confidence) and are home to 3 billion people.

Where they are: describing the pattern

• Hot deserts lie mostly in the subtropical trade-wind belts, such as the Sahara. Coastal deserts such as the Atacama and the Namib lie on the western edges of continents near the tropics.
• Cold environments: ice sheets cover most of Greenland and Antarctica. About 65% of Northern Hemisphere permafrost is in Eurasia and 35% in North America and Greenland.
• High mountains carry cold environments into lower latitudes: Glacier National Park in the Rockies, La Rinconada in the Andes, and the Tibetan Plateau, where the Qinghai–Tibet Railway, 960 km of it above 4,000 m, had to be built on permafrost.
• Exam move: describe a distribution as a pattern (latitude, continental position, altitude), with named examples and an exception.

Dryness, not heat, defines a desert

• The USGS summarises Peveril Meigs's 1953 scheme by rainfall: arid land gets less than 250 mm a year, semi-arid land 250–500 mm, and extremely arid land has at least 12 consecutive months without rain.
• "Arid and extremely arid land are deserts", while semi-arid grasslands are generally called steppes.
• The USGS also states that about one-third of Earth's land surface is desert, and that deserts "are always dry", whether hot or cold.

The aridity index

• Aridity index (AI) = mean annual precipitation ÷ potential evapotranspiration (P ÷ PET).
• PET is the water that would evaporate and transpire if water were always available.
• Classes: hyper-arid below 0.05; arid 0.05–0.20; semi-arid 0.20–0.50; dry sub-humid 0.50–0.65; humid above 0.65.
• Drylands (AI 0.65 or below) cover about 46% of land; the USGS's desert area is about one-third. Different definitions give different areas.

Why hot deserts are dry: the global pattern

• Subtropical high pressure: around 30° N and S, air that rose at the Equator sinks. It is dry "because its moisture has already been released near the Equator".
• Sinking air is compressed and warms, so clouds evaporate and rain rarely forms.
• Most non-polar deserts, including the Sahara, lie in the trade-wind belts.
• Continentality: midlatitude deserts lie in interior basins far from the oceans.

Why hot deserts are dry: local causes

• Rain shadow: air loses its moisture as it rises over mountains, then sinks and warms on the far side. Four mountain ranges lie between Death Valley, California, and the Pacific.
• Cold ocean currents: a cold current chills the air above it from below. Cool, stable air gives coastal fog but little rain.
• In the driest parts of the Atacama, measurable rain (1 mm or more) may fall only once every 5–20 years.

Why polar and high places are extreme

• Polar deserts get less than 250 mm of precipitation a year and have a warmest-month mean below 10 °C.
• Cold: the lowest air temperature recorded at a weather station was −89.2 °C, at Vostok, Antarctica, on 21 July 1983.
• Wind: Antarctic katabatic winds can exceed 100 km/h for days at a time.
• Altitude: temperature drops by about 2–3 °C for every 1,000 ft (about 300 m) climbed, and the air thins: half of the atmosphere's air lies below about 5.6 km.

Climographs: showing climate data (skills)

• A climograph plots monthly mean temperature (a line) and precipitation (bars) on one chart.
• Coober Pedy Airport, South Australia (hot arid), records from 1994 to October 2026: mean annual rainfall 144.1 mm; January mean maximum 36.9 °C, July 18.7 °C.
• Utqiaġvik, Alaska (Arctic coast), 1991–2020 normals: precipitation 5.39 inches a year (about 137 mm); the warmest month, July, averages 41.7 °F (5.4 °C).
• Exam move: describe the annual range, the wettest and driest months and any anomaly, quoting the figures.

Rain in hot deserts: unreliable and intense

• Unreliable: at Coober Pedy Airport (1994–2026), the wettest year had 308.2 mm (2016) and the driest 24.4 mm (2019), against a mean of 144.1 mm.
• Intense: storms are short and violent. 44 mm of rain once fell within 3 hours in the Sahara, and large Saharan storms may deliver up to 1 mm a minute.
• A long-term mean hides huge differences from year to year.

Flash floods

• Bare, hard ground lets little rain soak in, so water runs off fast into dry stream beds: wadis, also called arroyos or washes. They "fill temporarily during rain storms".
• Flash floods make these channels dangerous. The USGS states: "More people drown in deserts than die of thirst".
• UAE and northern Oman, 14–15 April 2024: Dubai's rain on 15 April was the highest daily total in its 75 years of records. At least 20 people died in Oman and four in the UAE.

Why April 2024 did so much damage (AO3)

• World Weather Attribution: urban surfaces with limited permeability, inadequate drainage and hyper-arid soils "exacerbate the risk and severity of flash floods".
• 80% of Oman's people and 85% of the UAE's live in flood-prone, low-lying areas.
• The rain was well forecast, but most deaths happened while people were travelling; warnings "may not have reached some people".
• Exam move: rare rain combined with high exposure and vulnerability still makes a high risk.

Mission 2: Many people in the Australian opal town of Coober Pedy live in homes dug into rock. Why live underground?

Why extreme environments challenge people

• Relief: steep slopes and high altitude.
• Climate: extreme heat or cold, drought, strong winds.
• Human discomfort: heat stress, cold stress, altitude sickness.
• Inaccessibility and remoteness: few roads and long distances to markets and services.
• All of these raise the cost of resource development: building, energy, water and labour.

Coober Pedy: hot and remote

• An opal-mining town in South Australia, about 850 km north of Adelaide. Opals were first found there in 1915.
• Population: 1,437 (2021 census).
• At Coober Pedy Airport since 1994: January mean maximum 36.9 °C; on average 24.2 days a year reach 40 °C or more; the highest temperature recorded there is 48.3 °C.

Living in the rock

• Many residents live in "dug-outs", homes cut into the sandstone. "Early dugouts began as mines".
• Underground, the temperature "is said to remain constant at around 23 degrees celsius" (State Library of South Australia).
• Water once had to be carried long distances; it now comes from an underground supply north of the town.

A resource draws people to a harsh place

• Sources differ on Coober Pedy's share of world opal: about 70% from its minefields (State Library of South Australia), or 90% together with the Mintabie fields (District Council of Coober Pedy). Quote each figure with its source.
• In the 2021 census, accommodation was the largest employing industry (11.8% of workers). Opal mining, counted as "other non-metallic mineral mining", employed 4.6%.
• The town grew on opal; today it depends on tourism too.

High and cold: La Rinconada, Peru

• La Rinconada lies at about 5,100 m in the Peruvian Andes. A 2020 study calls it "the highest city in the world" and describes its inhabitants as mostly involved in gold mining.
• Half of all the air in the atmosphere lies below about 5.6 km. At La Rinconada the air is thin, so the body receives less oxygen (hypoxia).

The human cost of altitude

• In a study of 1,594 adult volunteers (median age 32), seen at a medical consultation for miners' families, 44% had excessive erythrocytosis (too many red blood cells) and 14% had chronic mountain sickness.
• Their median time living there was 3 years.
• Human discomfort is a real cost, but a valuable resource can outweigh it.

Inaccessibility in the cold

• Over permafrost, thawed summer ground is often too marshy for roads. Supplies travel in winter on ice roads at least 100 cm thick, carrying trucks of up to 64 tonnes to mines and drill sites.
• Ice roads melt each summer and must be rebuilt every winter.
• Inaccessibility makes fuel, food, building materials and labour expensive.

Exam move: weighing the challenges (AO3)

• Compare challenges by group (residents, miners, companies, governments) and by scale (one home, one town, a region).
• Technology removes some challenges (dugouts, ice roads) but not others: no building restores the oxygen at 5,100 m.
• People accept extreme conditions when the reward (opal, gold, wages) is high enough.

Mission 3: Between 1941 and 2004, Alaska's Muir Glacier retreated 12 km. All that time, its ice kept flowing towards the sea. How can both be true?

A glacier is a system

• Inputs: snowfall and avalanches, mainly in the accumulation zone high on the glacier.
• Store: ice that flows downhill under its own weight.
• Outputs: melting, evaporation, sublimation (ice turning straight to vapour) and calving, mainly in the ablation zone lower down.
• Equilibrium line: the boundary between them, where a year's gain equals its loss.

Mass balance

• Mass balance = accumulation − ablation over a year.
• Positive: the glacier thickens and may advance. Negative: it thins and its snout may retreat. Glaciers grow "when winter snowfall exceeds summer melting".
• It is measured in water equivalent (w.e.): the depth of water if the ice gained or lost were spread evenly over the glacier.

How ice moves

• Internal deformation (creep): the weight of overlying snow, firn and ice deforms the ice.
• Basal sliding: a glacier may slide on a thin layer of water at its base, or on soft, wet sediment.
• Warm-based (temperate) glaciers: the base is at the pressure melting point, so meltwater lets them slide and erode strongly.
• Cold-based (polar) glaciers are frozen to their beds; they move mainly by deformation and erode little: "the movement at the bottom can be a tiny fraction of the speed of flow at the surface".

Advance and retreat over time

• At the last glacial maximum, glaciers covered about 32% of Earth's land; today they cover about 10%.
• In the Little Ice Age, glaciers advanced in many areas from about the early 14th century to the mid-19th (NSIDC). In Glacier National Park, Montana, it began around 1400 and glaciers peaked around 1850 (USGS).
• Glacier National Park had 80 glaciers larger than 0.1 km² at the Little Ice Age peak, and 32 in 2005, the latest count on this USGS page.

The global picture

• Glaciers worldwide lost 273 ± 16 gigatonnes of ice a year from 2000 to 2023.
• The loss was 36 ± 10% greater in 2012–2023 than in 2000–2011.
• About 5% of global glacier ice has gone since 2000, and between 2% and 39% in different regions.

Showing glacier change (skills)

• For long-monitored reference glaciers, the average loss each year was 214 mm w.e. in the 1980s, 499 in the 1990s, 527 in the 2000s and 896 in the 2010s (decade averages of annual mass balance, from World Glacier Monitoring Service data).
• From 1980 to 2018 their cumulative loss was 21.7 m w.e..
• Exam move: show glacier change as a cumulative mass-balance line or as decade-mean bars, with a zero line and units (m w.e. per year).

Glacial erosion

• Plucking: meltwater freezes onto rock at the bed, and moving ice tears blocks away. "As the ice moves, it plucks rock from the sides and bottom of the valleys" (NPS).
• Abrasion: rock fragments held in the base scrape and polish the bedrock like sandpaper, leaving scratches called striations.
• Freeze–thaw on the valley sides supplies more debris.

Transport and deposition

• Debris travels on the ice (supraglacial), within it (englacial) and beneath it (subglacial).
• The glacier carries debris downhill, "like a conveyor belt", and drops it at the far edge, where the ice is melting (NPS).
• Material dropped directly by ice is till: unsorted and angular, with all sizes mixed.

Mission 4: A 16,500-tonne boulder sits on the flat prairie of Alberta, Canada, far from the mountains it came from. How did it get there?

Reading a glaciated landscape

• Glacier National Park, Montana: "Massive U-shaped valleys, cirque lakes or tarns, horns, moraines, and arêtes".
• Erosional landforms dominate the high ground where glaciers formed; depositional landforms lie lower down, where the ice melted.
• Each landform is evidence of a process.

Cirques and tarns

• A cirque (corrie) is a round, steep-sided hollow carved at the head of a glacier, like a scoop taken out of the mountain.
• Ice turns in a rotational movement: plucking steepens the back wall, abrasion deepens the floor, and a rock lip is left at the front. After the ice melts, a small lake, a tarn, may fill the hollow.
• Example: Piegan Glacier still sits in a cirque on Piegan Peak.

Arêtes and horns

• Arête: a saw-toothed ridge left where two glaciers carved either side, such as the Garden Wall.
• Pyramidal peak (horn): a peak "scraped nearly vertical by glaciers on three or more sides", such as Reynolds Mountain, Flinsch Peak and the Little Matterhorn.
• Both form as cirques erode backwards towards each other (headward erosion).

Glacial troughs

• Rivers cut V-shaped valleys; glaciers scour them into U-shaped troughs, broad at the base with steep sides.
• Truncated spurs: the glacier cuts off the river's interlocking spurs, leaving steep cliffs along the trough.

Lakes and hanging valleys in troughs

• Long, deep lakes fill some troughs (ribbon lakes): Lake McDonald and St. Mary Lake.
• Hanging valleys: smaller tributary glaciers cut less deeply, so their valleys end high above the main trough. Bird Woman Falls pours from one.
• Paternoster lakes: a chain of small lakes down a valley, as in the Swiftcurrent Valley.

Moraines along the glacier

• Lateral moraine: debris along the valley sides, much of it from freeze–thaw on the walls above.
• Medial moraine: where two glaciers join, their lateral moraines merge into a stripe down the middle, as on Alaska's Gilkey Glacier.

Moraines across the valley

• Terminal moraine: a ridge at the snout's furthest point; the longer the snout stays in one place, the larger it grows.
• Recessional moraines: smaller ridges marking pauses as the ice retreats.
• Moraines record old ice limits: Glacier National Park's Little Ice Age maximum was reconstructed from them.

Erratics: Big Rock, Alberta

• An erratic is a rock carried by ice and dropped far from its source, often on a different type of bedrock.
• Okotoks "Big Rock": a 16,500-tonne quartzite boulder, about 9 m tall, 41 m long and 18 m wide.
• It was part of a mountain formation in what is now Jasper National Park. A rockslide dropped debris onto a glacier, which carried it out of the mountains; it arrived between 10,000 and 30,000 years ago.
• Exam move: landforms are evidence. Erratics trace the direction of ice movement and moraines its limits, but dating can be broad (here, a range of 20,000 years).

Mission 5: Near Tuktoyaktuk in Arctic Canada, a 49 m hill rises out of flat tundra. Its core is solid ice. How did it form?

Periglacial environments and permafrost

• Periglacial areas are cold, unglaciated areas shaped by frost; most have permafrost.
• Permafrost: ground at or below 0 °C for at least two years. It is "defined solely by temperature".
• Active layer: the top layer, which thaws each summer. Taliks: unfrozen ground within permafrost.
• About 85% of Alaska has some form of permafrost.

How much permafrost? It depends on the definition

• Zones: continuous (90–100% of the ground frozen), discontinuous (50–90%), sporadic (10–50%) and isolated patches (10% or less).
• NSIDC, using the International Permafrost Association map: permafrost underlies about 23 million km², or about 25%, of the Northern Hemisphere's exposed land.
• Obu et al. (2019), modelling ground temperatures for 2000–2016: permafrost covers 13.9 million km² (about 15%); all areas with any permafrost add up to about 21 million km² (22%).
• The larger figures count whole zones, even where only part of the ground is frozen.

Frost processes

• Freeze–thaw: water in cracks expands as it freezes and prises rock apart; repeated cycles shatter it.
• Frost heave: water drawn towards the freezing front builds ice lenses, which lift the ground and push stones upward. Under roads, "The expanding ice pushes up the road and creates a hump".
• Solifluction: the permafrost below acts "like a waterproof barrier", so the thawed active layer stays saturated and creeps slowly downslope, forming lobes.

Patterned ground and ice wedges

• Patterned ground: circles, stripes and polygons that form "when water and ice in the ground move the rocky soil around". In polar deserts the patterns can be up to 5 m across.
• Frost heave pushes stones up and outward, so they gather at the edges of circles and polygons (sorted patterned ground); on slopes, circles are drawn out into stripes.
• Ice-wedge polygons: frozen ground contracts and cracks in winter; water enters, freezes and widens the crack year after year.

Pingos

• Pingos are ice-cored hills 3–70 m high and 30–1,000 m across. They form only in permafrost.
• Closed-system pingos, like those near Tuktoyaktuk, form in recently drained lakes: unfrozen ground beneath the old lake (a talik) is surrounded by permafrost.
• As it freezes inward, water is pushed to the centre under pressure. It lifts the thin frozen layer above it and finally freezes into an ice core.
• Ibyuk Pingo is 49 m high and 300 m across: Canada's tallest, and one of about 1,350 pingos in the region.
• Open-system pingos, by contrast, form where groundwater under pressure rises through gaps in discontinuous permafrost and freezes.

Thermokarst

• Thermokarst: thawing ground ice "can gradually cave in", leaving "irregular surfaces of marshy bowls" and lakes.
• Permafrost can contain up to 80% ice; when it melts, the ground can collapse.
• Signs of thaw: thaw slumps, degraded ice-wedge polygons, thermokarst lakes and "drunken forests" of tilted trees.

Permafrost is warming (AO3)

• From 2007 to 2016, permafrost temperature rose by 0.29 ± 0.12 °C globally, and by 0.39 ± 0.15 °C in the continuous zone.
• From 1979 to 2021, the Arctic warmed nearly four times as fast as the globe.
• Degrading ice wedges, collapsing ground and new thermokarst lakes are therefore indicators of thaw.

Mission 6: Sand covers only about 20% of the world's deserts. What shapes the rest?

What desert surfaces are made of

• Sand covers only about 20% of Earth's deserts.
• Nearly 50% are plains where wind has removed fine material, leaving gravel: desert pavement.
• The rest: bare rock, desert soils, alluvial fans, playas and lakes.
• In Death Valley, California, less than 1% of the desert is covered by dunes.

Weathering by heat

• With little water, soil or plant cover, rock lies exposed to the Sun.
• On 15 July 1972 the ground at Furnace Creek, Death Valley, reached 201 °F (about 94 °C), while the air reached 128 °F (about 53 °C).
• Thermal (insolation) weathering: the outer layer of rock heats and cools faster than the inside. Repeated stress can open cracks and peel off sheets (exfoliation).

Physical weathering by salt and frost

• Salt weathering: as water evaporates, salt crystals grow in pores and force grains apart.
• Freeze–thaw works in cold-winter deserts too. At Arches National Park, Utah, "In winter, water trapped in cracks expands when it freezes, then contracts, prying the rock apart".
• Arches gets only about 8–10 inches (roughly 20–25 cm) of precipitation a year, yet that is enough.

Chemical weathering

• Solution: at Arches, rain "can slowly dissolve the calcite bonding the sand together" in the sandstone.
• Oxidation: iron minerals react with oxygen and turn red and orange.
• Desert varnish: a dark coat of manganese, iron oxides and clay minerals on long-exposed rock.
• Chemical weathering is slow because water is scarce, but dew and rare rain still drive it.

Wind: erosion and transport

• Deflation removes loose, fine particles; abrasion sand-blasts surfaces with wind-borne grains.
• The USGS lists suspension (particles under 0.2 mm held aloft as dust), saltation (sand moving in short hops) and surface creep (larger grains pushed along, up to 25% of grain movement).
• Wind-cut landforms: ventifacts (cut and polished rocks) and yardangs (streamlined ridges up to tens of metres high).

Dunes

• Barchans (crescentic dunes) form where wind blows from one direction. Some moved more than 100 m a year in China's Ningxia Province (1954–59).
• Linear (seif) dunes often form where winds blow from two directions, and may be more than 160 km long.
• Star dunes form where winds blow from many directions; in China's Badain Jaran Desert they reach up to 500 m.
• Sand climbs the gentle windward slope and avalanches down the steep slipface, so the dune moves downwind.

Water: wadis and flash floods

• The USGS notes that "water is much more powerful than wind"; in arid lands, water "is an important agent of erosion" (NPS).
• Wadis (arroyos, washes) are dry stream beds that fill during storms. Floods carry heavy loads of sediment "for a day or two".
• Where a channel leaves the mountains, it drops its load as an alluvial fan; fans can merge into a bajada.
• At Arches National Park, "Today, water shapes this environment more than any other force".

Mesas and buttes

• Mesa: a broad, flat-topped mountain with at least one steep side. Butte: a smaller flat-topped hill, steep on all sides. Spires are erosional remnants of buttes.
• A hard cap rock such as sandstone protects softer shale and siltstone beneath. As the soft rock erodes, the cap breaks off along joints.
• So mesas shrink to buttes, and buttes to spires. Example: Island in the Sky mesa and Junction Butte, Canyonlands National Park, Utah.

Rock pedestals

• A rock pedestal is a cap rock perched on a narrow shaft.
• The traditional textbook explanation is sand-blasting by the wind near the ground.
• Twidale and Campbell (1992) found that most pedestals are two-stage forms: moisture in the soil weathers the shaft below the surface, and erosion later strips the soil away to expose it.
• Exam move: a landform can have more than one explanation. Weigh the evidence for each.

Mission 7: From the 1960s, irrigation turned Central Asian desert into cotton fields. Later, the Aral Sea largely dried up and fields turned salty. How can watering a desert damage it?

Aridity is not infertility

• Aridity is a lack of water; infertility is a lack of nutrients or poor soil structure.
• Desert soils are mostly mineral soils with low organic content; some contain salt layers or hard calcrete.
• Given water, desert soils can be highly productive: in Central Asia, "irrigation made the desert bloom" (NASA).

Access to irrigation water

• Exotic rivers bring water from outside the desert: the Nile, the Colorado and the Yellow River.
• Oases, fed by springs, wells or irrigation, are often the only places in deserts with crops and permanent settlement.
• Covered underground channels carry mountain water into China's Turpan Depression, so it does not evaporate on the way.
• Whoever controls the water controls who can farm.

The Aral Sea

• In the 1960s, the Soviet Union diverted the Syr Darya and Amu Darya rivers to irrigate cotton and other crops.
• The Aral Sea, once the world's fourth-largest lake, shrank. The eastern lobe of the South Aral disappeared completely in 2014.
• Fisheries collapsed, and salty dust contaminated with farm chemicals blew onto fields and degraded the soil.

How irrigation makes soil salty

• All irrigation water carries dissolved salts. In hot, dry air much of the water evaporates and the salt stays behind.
• Over-watering and poor drainage raise the water table. Water rises through the soil and evaporates at the surface, leaving more salt.
• This is secondary salinisation. Half of Central Asia's irrigated lands, especially in the Amu Darya and Syr Darya basins, were affected (Qadir et al., 2009, cited by the IPCC).

Salinisation worldwide

• FAO, from 1970–80 soil maps: 45 million ha of the then 230 million ha of irrigated land were salt-affected, a share FAO gives as 19.5%.
• FAO's Global Map of Salt-Affected Soils: more than 424 million ha of topsoil and 833 million ha of subsoil are salt-affected. More than two-thirds of these soils lie in arid and semi-arid climates.
• FAO warns that estimates made by different methods "are difficult to compare".

Managing water and salt

• Ways to reduce salinisation: drip irrigation, drainage to lower the water table, flushing salts with extra water, and salt-tolerant crops. FAO notes that farmers on salty land may be "forced to cultivate salt-tolerant crops" that do not pay as well.
• In the Aral basin, croplands "had to be flushed with larger and larger volumes of river water": a trade-off.
• Kazakhstan's Kok-Aral dike and dam, finished in 2005, let the North Aral and its fisheries rebound, but limited flow into the South Aral.

Land ownership and tenure (AO3)

• IPCC: secure land tenure is a major factor in farmers adopting soil conservation (high confidence).
• Privatising rangeland in Botswana and Kenya cost pastoralists their communal grazing and "actually increased rangeland degradation".
• Resilience to climate risks is higher where tenure is flexible enough for pastoralists to move their herds (robust evidence, high agreement).

Mission 8: About half of the 800-mile Trans-Alaska Pipeline runs above the ground. Why not bury all of it?

Case study: Alaska's North Slope

• Oil was discovered at Prudhoe Bay, on Alaska's Arctic coast, in 1968.
• North Slope oil fields feed the Trans-Alaska Pipeline System (TAPS): 800 miles (about 1,290 km) from Deadhorse south to the port of Valdez. It was completed in 1977, when major North Slope production began, and has carried more than 18 billion barrels.
• North Slope output was 468.0 thousand barrels a day in fiscal year 2025, and is forecast at 517.8 thousand in 2027.

Physical challenge: permafrost

• About 85% of Alaska has some form of permafrost.
• When TAPS was designed, oil in the pipe was expected to be at 158–176 °F (about 70–80 °C); that hot, it "would thaw a cylindrical area 20 to 30 feet in diameter within a decade". Thawed permafrost could let the pipe sink and break.
• Today's oil is cooler, but still well above freezing: in 2016 it entered the line at about 104 °F (40 °C) and reached Valdez at about 40 °F (4 °C) (a trade report).
• So the pipe is raised on supports for 420 miles where the permafrost is unstable, with devices that release heat into the air.
• The 380 buried miles run through thawed soils, bedrock, or permafrost whose thaw would not damage the pipe; 4 of them are buried in permafrost with their own refrigeration.

A warming climate threatens the infrastructure

• From 1979 to 2021, the Arctic warmed nearly four times as fast as the globe.
• Hjort et al. project that by mid-century (2041–2060) 550 km of TAPS lies where near-surface permafrost may thaw: a projection, not an observation.
• Inaccessibility adds cost: in summer the thawed tundra is too marshy for roads (2.8).

Human opportunity: oil revenue

• In fiscal year 2025, petroleum revenue was $1,910.5 million of Alaska's $6,342.2 million unrestricted general fund revenue.
• Alaska's constitution requires that "At least twenty-five per cent" of mineral lease rentals, royalties and bonuses received by the State go into a permanent fund. In 2025 the Permanent Fund contributed $3.7 billion to unrestricted revenue.
• Oil wealth has been turned into a long-term investment.

Who owns the land and the oil?

• The pipeline runs on State land for 580 of its 800 miles. In May 2026 the State also acquired nearly 1.4 million acres along the corridor from the federal government.
• Federal land: the 23-million-acre National Petroleum Reserve in Alaska, where the Willow project is under construction, with first oil planned for 2029.
• The Alaska Native Claims Settlement Act (1971) settled Alaska Native land claims; regional and village corporations selected land.
• TAPS is owned by three companies: Harvest Alaska, ConocoPhillips and ExxonMobil.

Resource nationalism

• Resource nationalism: a government asserting greater control over the natural resources in its territory, and a bigger share of their wealth, through state ownership, state companies, taxes or limits on foreign firms.
• Greenland, under self-government, took over responsibility for mineral resources on 1 January 2010, assuming "the right to utilise the mineral resources found in the subsoil".
• Alaska is a weaker example: a US state, not a nation, keeps royalties and a savings fund. Chile's lithium (Mission 9) shows the national form.

Evaluating the case (AO3)

• Benefits: State revenue, jobs, and a savings fund that can outlast the oil.
• Risks: spills of more than 55 gallons averaged about 7.6 a year in 1977–1994 and 1.5 a year in 1995–2025; thawing permafrost threatens infrastructure.
• Scale: across the Russian Arctic, 45% of hydrocarbon extraction fields lie in regions that Hjort et al. class as high hazard for thaw-related ground instability by mid-century (a projection).
• Stakeholders: State and federal governments, oil companies (TNCs such as ConocoPhillips and ExxonMobil), Alaska Native corporations.

Mission 9: Under a salt flat in the Atacama, one of the driest places on Earth, lies brine rich in lithium. Who decides who pumps it?

Case study: the Salar de Atacama, Chile

• Lithium is drawn from brine, salty groundwater, beneath the Salar de Atacama, a salt flat in Chile's Atacama Desert.
• Batteries account for 88% of world lithium use.
• Chile, with two major brine operations, produced an estimated 56,000 t of lithium in 2025, out of a world total of about 290,000 t. Chile holds 9.2 million t of the world's 37 million t of reserves.

Physical opportunities and challenges

• Climate as an opportunity: in the dry, sunny climate, brine has traditionally been concentrated by solar evaporation in large ponds.
• Climate as a challenge: the USGS says measurable rain may fall only once every 5–20 years in the Atacama's driest parts. The salar itself, on the desert's eastern side, gets roughly 20–60 mm a year, mostly in summer, so water is scarce for people, farms and wetlands.
• Inaccessibility: the salar lies at about 2,300 m in a remote basin. Calama, the nearest city, is about 190–220 km away by road and Antofagasta about 270–280 km (the companies' reports differ with their sites). Paved roads and grid power (since 2017) now reach it.

Political factors: the state keeps lithium

• In Chile, lithium is "not concessible", so it cannot be put out to tender like other minerals (translated).
• SQM's lease from the state development agency Corfo expires in 2030.
• In April 2023, President Gabriel Boric presented the National Lithium Strategy, which required direct state participation in lithium production in the Salar de Atacama.

The Codelco–SQM deal

• State copper company Codelco and private Chilean firm SQM, which has sales networks in several countries, signed a partnership on 31 May 2024. Their joint company, Novandino Litio (written "Nova Andino Litio" in its first press release), has licences to extract brine until 2060.
• The companies estimate that the state will receive up to 70% of the operating margin on new production in 2025–2030, and up to 85% from 2031.

Competing stakeholders: TNCs, communities and civil society

• Atacameño (Lickanantay) indigenous communities live around the salar. A Corfo-led indigenous consultation on the deal ran from May to September 2025.
• Albemarle, a US-based TNC, also mines the salar. Its Chilean company "contributes 3.5% of its annual sales" to the Council of Atacameño Peoples (CPA).
• An article by Fundación Tanti, a Chilean NGO, reports that the announcement of the Codelco–SQM memorandum of understanding revived Lickanantay protests in late 2023 and early 2024.
• Drawing on members of the civil-society network OPSAL, it argues that consultation is not binding and does not guarantee free, prior and informed consent, and warns of a "green sacrifice zone" (translated).

Technology and the water dispute (AO3)

• The partners say their Salar Futuro project will make more lithium "with less brine and no use of continental water" (project website).
• Their own questions and answers are more careful: no increase in brine extraction or in continental-water use compared with current consumption, an aim to "move towards zero" continental water, and gradual replacement of pond evaporation with mechanical evaporation (translated). Fresh water now comes from wells in the basin.
• The NGO critique: the impact study gives no year-by-year water balance, and does not show that reinjecting up to 700 litres a second of brine will leave the salar's microbes unharmed.
• Exam move: attribute each claim (state, company, NGO), then judge it on the evidence each offers.

Militia groups and desert gold

• UNODC, on the Sahel: "Armed groups are reported to extract payments from the gold sector by exercising their authority over ASGM mine sites or controlling transportation routes to and from mine sites". ASGM is artisanal and small-scale gold mining.
• UNODC recommends two responses: to "confront criminal groups and their illegal activities with criminal justice responses", and to "support ASGM formalization with legal frameworks" that are "supportive and accessible rather than punitive".
• Exam move: contrast power. In Chile the state controls lithium by law; where state authority is weak, armed groups can extract payments from a resource.

Mission 10: In 2019 the climb up Uluṟu closed for good, yet the park remains open to visitors. Why close one of Australia's most famous attractions?

Why tourists visit extreme environments

• Attractions: scenery, wildlife, wilderness and culture; remoteness itself can be part of the appeal.
• Challenges: the cost of access, safety, short seasons and fragile environments that recover slowly.
• Stakeholders range from local (residents, Traditional Owners, local firms) to global (tour companies, international bodies, visitors).

Antarctica: growth and pattern

• Tourism grew from about 6,700 landed passengers in 1992–93 (IAATO's historical table) to over 100,000 passengers a year today.
• About 98% of voyages go to the Antarctic Peninsula, a few days' sail from South American ports, between October and April.
• In 2025–26, 113,518 people travelled with IAATO members, including 27,217 on cruise-only ships that did not land. Numbers fell 4.2% on 2024–25.

Managing Antarctic tourism: global stakeholders

• Treaty parties meet as the Antarctic Treaty Consultative Meeting (ATCM), which sets regulations and site guidelines. IAATO, the operators' association, attends as an invited expert.
• The ATCM's General Guidelines for Visitors (Resolution 4, 2021) state that "Vessels with more than 500 passengers shall not make landings", allow at most 100 passengers ashore at once, and require one guide per 20 passengers.
• IAATO adds its own measures for members: a central scheduling system to prevent overcrowding, and whale slow-down zones.
• The 1991 Environment Protocol bans all mineral resource activity except research. Neither it nor the Treaty has an end date: the claim that it "expires" in 2048 "is not correct".

Uluṟu: local stakeholders

• Uluṟu-Kata Tjuṯa National Park was handed back to its Traditional Owners, the Aṉangu, in 1985, and has been jointly managed with the Australian Government ever since.
• Its board of management has 12 members, eight of them Aboriginal members nominated by Traditional Owners.
• 25% of park-pass revenue goes to Aṉangu as lease payments, supporting homelands, training and business development.

Uluṟu: tourism in a hot, dry place

• At nearby Yulara Airport (1983–2026), mean annual rainfall is 267.5 mm and the January mean maximum is 38.6 °C: a semi-arid climate by the USGS's rainfall thresholds.
• The park warns that heat exhaustion and dehydration "are very real dangers here", advises walkers to "Carry and drink at least one litre of water per person per hour", and asks visitors not to walk on "tracks that are closed due to the heat".
• Heat limits when, and how far, visitors can walk: a tourism challenge.

Why the climb closed

• Uluṟu is sacred to Aṉangu, and climbing it "was not generally permitted under Tjukurpa" (Aṉangu law).
• Visitors began climbing in the late 1930s, and a chain was installed in 1964. From the 1990s, signs asked visitors not to climb, and the number climbing fell.
• In November 2017 the board voted unanimously to close the climb; its criteria included the share of visitors climbing falling below 20%. It closed on 26 October 2019.

Evaluating tourism management (AO3)

• Antarctica: visitors now exceed 100,000 a year. Treaty guidelines limit landings, and IAATO's scheduling spreads the impact, but guidelines and industry self-regulation rely on operators complying.
• Uluṟu: Traditional Owners hold most seats on the board and receive 25% of park-pass revenue. The board set a criterion that the share of visitors climbing fall below 20% before closing the climb.
• Exam move: weigh who decides, who benefits and how well impacts are limited: global rules plus self-regulation in Antarctica; joint local management at Uluṟu.

Mission 11: Between 11,000 and 5,000 years ago, the Sahara had permanent lakes, plants and people. Today it is desert. Did people cause the change?

What desertification is

• IPCC: "Desertification is land degradation in arid, semi-arid, and dry sub-humid areas", resulting from many factors, including human activities and climatic variations.
• It means drylands losing productivity, not simply dunes advancing. Its range and intensity have increased in some dryland areas over recent decades (high confidence).
• Deserts have grown and shrunk naturally: about 18,000 years ago, sand seas covered almost 50% of the land between 30° N and 30° S, against about 10% today.

Natural desertification: the Green Sahara

• From 11,000 to 5,000 years ago, the Sahara had high rainfall, varied vegetation, permanent lakes and people. Wet conditions reached 31° N.
• It was one of a series of wet phases paced by slow changes in Earth's orbit (precession), which raised northern-summer sunshine and strengthened the African monsoon.
• As that forcing faded, the monsoon retreated. Tierney et al. find the wet period's high rainfall "best explained by strong vegetation and dust feedbacks". The IPCC adds that a cooling of the north Atlantic played a role.

Case study: the Sahel's rainfall

• The Sahel is the semi-arid belt along the southern edge of the Sahara.
• Summer rainfall was high in the 1950s and 1960s, fell sharply in the 1970s and 1980s (the driest year in the index was 1984) and has partly recovered since.
• IPCC: "a cooler north Atlantic is related to a drier Sahel"; aerosols have also been suggested as a driver of the droughts.

Human causes and acceleration

• Croplands in the West African Sahel doubled after 1975, and settlement area grew by about 150%.
• Overgrazing in the Sahel reduced the seed bank of annual plants, leaving them more vulnerable to climate change.
• The major human drivers interacting with climate change: cropland expansion, unsustainable land management, and population and income growth.
• Positive feedback: bare soil loses more water to runoff and more soil to wind, so plants struggle to return.

Is the Sahel desertifying? Weighing the evidence (AO3)

• IPCC: despite concern since the 1970s, "wetting and greening conditions have been observed in this region over the last three decades".
• One analysis found climate the dominant cause of greening in 1982–2003, with pockets of desertification in Nigeria and Sudan.
• Studies disagree because they use different indicators, sites, methods and scales. The relative roles of climate and people "are location-specific and evolve over time" (high confidence).

Consequences

• The Sahel droughts of the 1970s–80s brought hunger, out-migration and suffering for millions of pastoralists.
• Desertification has reduced agricultural productivity and incomes (high confidence).
• Dust storms were associated with about 402,000 deaths from heart and lung disease worldwide in 2005, about 1.8% of such deaths (IPCC, citing a modelling study).

Desertification and conflict (AO3)

• The IPCC cites a suggestion that droughts and desertification played "a relatively minor role" in the Sahel's 1980s conflicts, the major reasons being political, especially the marginalisation of pastoralists. It also cites a study finding that greater dryness raised the likelihood of riots across Sub-Saharan Africa.
• Insecure tenure can in turn worsen degradation where herders cannot move freely (see 7.8).
• Exam move: avoid environmental determinism. Weigh environmental, political and economic causes.

Management: the Great Green Wall

• Launched by the African Union in 2007 to restore 100 million ha of degraded land by 2030, across 11 core countries. It aims to grow a "mosaic of trees, grasslands, vegetation and plants", not a single line of trees.
• Its length is given as 8,000 km, from Senegal to Djibouti (UNCCD), or 7,775 km, from Senegal to Eritrea (IPCC).
• In 2011–2017, about 4 million ha were restored in the intervention areas, 2.3 million ha of them in Ethiopia. Other sources give almost 17.8 million ha in the wider region.

Evaluating the responses (AO3)

• IPCC: past reforestation in the Sahel and North Africa was "poorly studied and cost a lot of money without significant success"; reaching the targets is "questionable, and will be challenging without significant additional funding".
• Local techniques: zaï pits and stone bunds harvest rainwater, and there is robust evidence that rainwater harvesting raises dryland yields.
• Each USD invested in restoring degraded land yields USD 3–6 in social returns over 30 years, yet adoption of sustainable land management stays low: most returns are social, while farmers bear high initial costs.

Mission 12: Shishmaref, an Iñupiaq village on an Alaskan island, has voted three times to move. Why, and why is it still there?

Climate change in extreme environments

• Cold: from 1979 to 2021, the Arctic warmed nearly four times as fast as the globe; permafrost warmed by 0.29 °C from 2007 to 2016; glaciers have lost about 5% of their ice since 2000.
• Modelling projects near-total loss of Glacier National Park's glaciers by 2100.
• Hot drylands: "Climate change will exacerbate several desertification processes" (IPCC, medium confidence). With 2 °C of warming (a middle-of-the-road pathway), about 1,152 million dryland people are projected to be exposed to impacts such as water stress and drought.

Impacts on people and infrastructure

• Nearly four million people and 70% of current infrastructure in the permafrost domain are in areas with high potential for near-surface thaw by 2050 (projection).
• When permafrost thaws, "buildings tilt, roads buckle and dip".
• Saami reindeer herders in Sweden have observed thawing ground in summer grazing areas since the mid-1990s, leading to "soggy falls and rotten spring vegetation".

Shishmaref, Alaska

• About 500 people live in Shishmaref, on a barrier island near the Bering Strait only about a quarter of a mile wide.
• NSIDC reports that sea ice once protected the shore, but that since the 1980s summer sea ice has become less predictable, so waves batter the permafrost coast and about 7 m of land washes away each year.
• Residents moved buildings back, laid rocks and sandbags and built seawalls. They voted to relocate in 1973, 2002 and 2016.
• NSIDC cites a US Army Corps of Engineers report (undated in the source) that put the cost of moving at about $179 million.

Adaptation in hot drylands

• The IPCC highlights rainwater harvesting, including traditional zaï pits, as a measure of "increasing importance under climate change" (see 11.11).
• After the 2024 floods in the UAE and Oman, World Weather Attribution called for more proactive urban planning and impact-based forecasting in warning systems.
• At Uluṟu, walkers are advised to avoid the hottest hours, and in summer not to walk after 11.00 am.

Mission 13: Deserts get more sunshine than they can use, and many lie beside the sea. Can technology turn sun and seawater into reliable power and water?

New technology: solar power

• Deserts get strong sunshine: Coober Pedy averages 28.3 MJ/m² of solar exposure a day in January (1990–2026).
• Morocco's Noor-Ouarzazate concentrated solar power (CSP) complex: the World Bank backed the first, 160 MW phase of a planned 500 MW plant (approved 2011), then Noor II and III (2014), to raise output "especially during peak hours".
• The project included a mechanism to cover the gap between the price the Moroccan solar agency pays for the power and the price at which it sells it: solar power needed support.
• IPCC: stronger sand storms and moving dunes are causing disruption and damage to solar and wind energy infrastructure (high confidence).

New technology: desalination

• A 2019 global synthesis found 15,906 operational desalination plants producing about 95 million m³ of water a day, 48% of it in the Middle East and North Africa.
• It estimated brine at about 142 million m³ a day, with Saudi Arabia, the UAE, Kuwait and Qatar accounting for 55%.
• Brine disposal is "both costly and associated with negative environmental impacts".

Is new technology sustainable? (AO3)

• A model study cited by the IPCC projects that very large wind and solar farms in the Sahara could double rainfall in the Sahel, through more surface friction and lower albedo. It is a model projection, not an observation.
• Judge each technology by who benefits, what it costs, its side effects (brine, dust, land use) and its scale.
• Sustainable development meets today's needs without harming the ability of future generations to meet theirs.

How Option C is examined (Paper 1)

• Paper 1 tests the options. SL students answer two options in 1 hour 30 minutes (40 marks, 35% of the grade); HL students answer three in 2 hours 15 minutes (60 marks, 35%).
• Each option has a structured question (10 marks) and one extended answer from a choice of two (10 marks): 45 minutes per option.
• The extended answer is marked with markbands from 0 to 10, two marks per band.

What the top band rewards (extended answer, 9–10 marks)

• The answer is "in-depth and question-specific (topic and command term)".
• Examples, statistics and details are integrated and explained, not listed: Coober Pedy's 115 mm in a day, or the Great Green Wall's two progress figures.
• Evaluation sets out cause and effect, other perspectives, and the strengths and weaknesses of evidence. The conclusion is balanced and matches the evidence.
• Maps and diagrams are annotated, follow conventions and support the argument.

Command terms and a 10-mark plan

• Explain: "Give a detailed account including reasons or causes." Evaluate: "Make an appraisal by weighing up the strengths and limitations." Discuss: "Offer a considered and balanced review that includes a range of arguments, factors or hypotheses".
• Plan for "Evaluate the management of desertification in one named region" (10 marks): define desertification (11.1); weigh the Great Green Wall's target against its two progress figures (11.9–11.10); add the IPCC's cost and success caveats (11.11); set zaï and land tenure against them (11.11, 7.8); conclude on scale and on who benefits.

The big ideas

• Extreme environments are cold and high, or hot and arid. Dryness, not heat, defines a desert (Antarctica; Utqiaġvik).
• Desert rain is rare, unreliable and intense, so flash floods are a real risk (UAE and Oman, 2024).
• People live and work in extremes when resources reward them, and adapt (Coober Pedy; La Rinconada; ice roads).
• Glaciers are systems: mass balance drives advance and retreat; plucking and abrasion carve cirques, arêtes, horns and troughs; ice deposits moraines and erratics.
• Permafrost makes frost heave, solifluction, patterned ground, pingos and thermokarst. In deserts, weathering, wind and water make pavements, dunes, wadis, mesas, buttes and pedestals.
• Irrigation can make deserts productive but salty (Aral Sea). Oil and lithium bring wealth, permafrost problems, resource nationalism and competing stakeholders (Alaska; Atacama).
• Tourism, desertification, climate change and new technology: always ask who decides, who benefits, and what the evidence shows.

Final screen. Score, the mission list ticked, and "Next: test yourself in the Verify stage" (links to the Verify quiz).