Climate: quotes, facts and reflections

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WonderScience

Ice drilled from deep in Antarctica holds tiny bubbles of ancient air, letting scientists measure what the atmosphere was like up to 800,000 years ago.

An ice core is a long cylinder of ice drilled out of a glacier or ice sheet. As snow piles up and is pressed into ice over centuries, it traps small pockets of the surrounding air, along with dust and chemical traces. The European EPICA core from Dome C, in East Antarctica, gives a continuous record going back about 800,000 years. By measuring the gas in the bubbles, scientists can read past levels of carbon dioxide and methane directly, and match them with ice ages, warm periods and volcanic eruptions recorded in the same layers. In early 2025 a follow-up project, Beyond EPICA, finished drilling nearby to a depth of 2,800 metres and reported ice that may extend the record to 1.2 million years.

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WonderScience

Mangroves, trees that grow in salt water on tropical coasts, protect shorelines by slowing waves and store large amounts of carbon in the mud beneath them.

Mangrove roots, some sticking up out of the mud like snorkels to take in air, slow waves, trap sediment and limit erosion, and their tangle of underwater roots shelters fish, crabs and young sea creatures. Mangrove forests also hold large amounts of 'blue carbon', the name for carbon stored by coastal and ocean ecosystems. Much of it lies in the waterlogged, oxygen-poor mud, where dead plant matter rots so slowly that carbon can stay buried for centuries. Studies of tropical forests have found that, area for area, mangroves are among the most carbon-rich forests on Earth. Clearing them for shrimp farms or building therefore releases carbon as well as destroying habitat and natural coastal defences.

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WonderScience

Peatlands cover only about 3 percent of the world's land, yet hold roughly twice as much carbon as all its forests. They form as partly rotted plants pile up in waterlogged ground over thousands of years.

Peat is the dark, spongy material that builds up where waterlogged, oxygen-poor ground slows the decay of dead plants almost to a stop; mosses, especially sphagnum, are often its main source. It grows very slowly, around a millimetre a year, so a few metres of peat can hold thousands of years of history. Peatlands range from the bogs of Ireland and Scotland to vast areas of Siberia and Canada, and to tropical peat swamps in Indonesia and the Congo Basin. When they are drained for farming or forestry, or catch fire, carbon that took millennia to build up can escape within years. That is why rewetting drained peatlands is now part of many countries' climate plans.

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WonderScience

The ozone layer, which shields life from harmful ultraviolet light, is slowly recovering because countries phased out ozone-destroying chemicals under the 1987 Montreal Protocol.

Chlorofluorocarbons, or CFCs, were once common in aerosol sprays, fridges, air conditioners and foam. In the 1970s scientists showed that high in the atmosphere they release chlorine, which destroys ozone, and in 1985 British researchers reported a deep seasonal thinning over Antarctica, the 'ozone hole'. The Montreal Protocol, agreed in 1987, set a timetable for phasing these chemicals out, and it became the first treaty in United Nations history to be ratified by every member state. The 2022 scientific assessment carried out under the treaty found the ozone layer on course to return to its 1980 state around 2040 over most of the world, around 2045 over the Arctic and around 2066 over Antarctica.

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StillnessScience

Seagrass meadows cover only about 0.1% of the seafloor, yet they account for roughly a tenth of the carbon buried in ocean sediments. Seagrasses are flowering plants that grow underwater along coasts.

Unlike seaweeds, which are algae, seagrasses have roots, leaves and flowers, and they grow in shallow coastal water on every continent except Antarctica. Their leaves slow the current so fine particles settle, and their roots bind the seabed. Dead leaves and roots are buried in mud with little oxygen, where they rot very slowly, so their carbon can stay locked away for centuries. Carbon stored by coastal plants in this way is called blue carbon. In the Mediterranean, including the Turkish coast, Posidonia oceanica meadows build thick mats of roots and sediment over thousands of years. Since the late nineteenth century, more than a fifth of the world's known seagrass area has been lost to dredging, pollution and coastal building.

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DriveScience

Beavers build dams of branches and mud that turn streams into ponds and wetlands, raising the water table and reshaping whole valleys.

Beavers build dams to create deep water around their lodges, where they can hide from predators and store branches for winter. The ponds slow floods, trap silt and keep the ground wet through dry spells, making room for fish, frogs, insects and birds. Because their work creates habitat for so many others, ecologists call beavers ecosystem engineers. A 2020 study of wildfires in the western United States found that stretches of stream dammed by beavers stayed green while the land around them burned. Some land managers now reintroduce beavers, or build simple beaver-style dams of posts and branches, to restore streams. Beavers can also flood farmland and roads, so they are not welcome everywhere.

U.S. Fish & Wildlife ServiceRead card

DriveTechnology

A Passive House is a building designed like a thermos: carefully sealed, insulated and ventilated so it wastes very little energy.

Passive House is a performance standard, not an architectural style: any building that meets its measured limits can qualify. The idea grew from a 1988 conversation between Bo Adamson of Lund University in Sweden and the German physicist Wolfgang Feist. Four terraced houses built in Darmstadt-Kranichstein, Germany, in 1990–91 are usually cited as the first examples. Feist founded the Passivhaus Institut in Darmstadt in 1996 to certify buildings. The best-known limits are a yearly heating demand of no more than 15 kilowatt-hours per square metre of floor, and an airtightness test in which a fan pressurises the building and no more than 0.6 of its volume of air may leak out in an hour. Fresh air comes in through a ventilation unit that warms it with the heat of the stale air going out.

Passive House InstituteRead card

DriveScience

Cities are often a few degrees warmer than the countryside around them, an effect called the urban heat island. Asphalt, concrete and dark roofs soak up the sun's heat and give it back slowly, while streets without trees get no shade.

The effect was first described in the 1810s by Luke Howard, a London manufacturing chemist and amateur meteorologist, who found that the centre of London stayed about 2°C warmer at night than the surrounding countryside. In the United States, the Environmental Protection Agency puts the typical difference at roughly 0.5 to 4°C by day and 1 to 3°C at night. The gap is often widest after dark, when concrete and asphalt release the heat they stored during the day. Cities respond with pale, reflective pavements and roofs, green roofs and street trees, because shade and light-coloured surfaces measurably lower local temperatures. The heat also falls unevenly: neighbourhoods with fewer trees and more paving are usually the hottest.

U.S. Environmental Protection AgencyRead card

WonderArchitecture

A windcatcher, badgir in Persian, is a tall tower on a roof that catches passing breezes and channels them down into the rooms below. It has cooled houses in hot, dry places such as Iran for centuries, without any machinery.

The top of the tower has openings that face the wind. Air pushed in is forced down a shaft into the house, while warm air leaves through openings on the sheltered side; on still days the sun-warmed tower works like a chimney and draws air through the rooms. Yazd, a desert city in central Iran listed by UNESCO in 2017, is famous for its many windcatchers, and the one in its Dowlatabad Garden, about 33 metres high, is often described as the tallest in the world. Paired with covered water reservoirs called ab-anbars, windcatchers helped keep drinking water cool. Similar towers are found from Egypt to the Persian Gulf, and architects now study them for low-energy cooling.

Traditional Persian architectureRead card

WonderEngineering

A qanat is an underground channel, developed in ancient Persia, that brings groundwater from the foot of hills to fields and towns using gravity alone. From above, a qanat shows as a line of shaft openings across dry land.

Builders start with a 'mother well' dug down to the water table, then cut a tunnel back towards the surface on a very gentle slope, so the water flows without wearing away the channel. Vertical shafts along the route let workers lift out soil, bring in air and later clean the tunnel. The Qasabeh qanat at Gonabad in eastern Iran, dated to between 700 and 500 BCE, has a mother well more than 360 metres deep and about 33 kilometres of channels, and still carries water. In 2016 UNESCO listed eleven Iranian qanats together as a World Heritage site, recognising both the engineering and the old customs for sharing the water fairly.

Qanat water systemsRead card

WonderClimate

When Syria's civil war cut the agricultural research centre ICARDA off from its genebank near Aleppo, it turned to the backup seeds it had stored in the Svalbard Global Seed Vault in Arctic Norway. Those seeds were used to rebuild its collections in Lebanon and Morocco.

ICARDA, the International Center for Agricultural Research in the Dry Areas, kept one of the world's major collections of wheat, barley, lentil and other crop varieties at Tel Hadya, near Aleppo. A genebank stores seeds alive for plant breeders and researchers, and between 2008 and 2014 ICARDA sent duplicates of 116,484 samples to Svalbard. The vault, opened in 2008, is dug into a mountain on an Arctic island and keeps seeds frozen at about minus 18°C. ICARDA withdrew seeds in 2015, the first withdrawal in the vault's history, and again in 2017 and 2019, until every sample had come back. Once the seeds had been grown again in Lebanon and Morocco, fresh duplicates were returned to Svalbard.

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WonderMigration

Eastern monarch butterflies fly up to 4,800 kilometres from Canada and the United States to the mountains of central Mexico each autumn, yet no single butterfly makes the whole round trip: the yearly cycle takes about four generations.

The butterflies that fly south in late summer are a special generation: they live about eight months, while the summer generations before them live less than two. They spend the winter packed by the million on oyamel fir trees in the mountains of Michoacán and the State of Mexico, then start north in spring, lay eggs on milkweed in the southern United States and die. Milkweed is the only food their caterpillars eat. Their children and grandchildren carry on northwards. Where the monarchs wintered was a mystery until January 1975, when Kenneth Brugger and Catalina Aguado (later Trail), volunteers helping the Canadian zoologist Fred Urquhart, found the first colony.

Monarch butterfly migrationRead card

WonderArchitecture

Machu Picchu, a 15th-century Inca estate on a ridge high in the Peruvian Andes, stands on hundreds of stone terraces. They hold the steep soil in place, drain away heavy rain and gave the Inca room to grow crops.

It was built around 1450 as a royal estate for the Inca ruler Pachacuti, at about 2,430 metres. Much of its engineering is hidden: studies led by the hydrologist Kenneth Wright suggest that some 60 per cent of the construction lies underground, in foundations and layers of crushed stone that let the frequent heavy rain drain away instead of washing the slopes down. The site was never truly lost. Local Quechua farmers always knew it, and the Peruvian Agustín Lizárraga reached it in 1902. The American explorer Hiram Bingham made it world-famous in 1911. UNESCO listed it as a World Heritage Site in 1983.

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WonderArchitecture

The Great Mosque of Djenné in Mali, often called the largest mud-brick building in the world, survives because the whole town re-plasters its walls with fresh mud every year before the rains.

The present building was completed in 1907 under Ismaila Traoré, head of the town's guild of masons, on the site of a mosque said to date from the 13th century. Its walls are made of sun-dried mud bricks, and bundles of palm wood jutting from them serve as permanent scaffolding. Rain wears the plaster away each year, so every spring the town holds a festival, the Crépissage, to renew it. Men and boys race to carry baskets of mud up the walls, women bring water from the river, and the elders of the masons' guild direct the work. Djenné's old town has been a UNESCO World Heritage Site since 1988.

Great Mosque of DjennéRead card

WonderArchitecture

Petra, the rock-carved city of the Nabataeans in southern Jordan, could thrive in the desert thanks to its water engineering: channels, dams, cisterns and reservoirs that caught springs, rain and flash floods.

The Nabataeans were an Arab people who grew rich from the caravan trade in incense and spices, and Petra was their capital. The city was at its height around the 1st century AD, until Rome annexed the kingdom in AD 106. In a region that gets only about 15 centimetres of rain a year, its channels, dams, tunnels and cisterns stored water through the dry months; the American Society of Civil Engineers estimates the system supplied 30,000 to 40,000 people. As trade routes shifted and earthquakes struck, the city declined. The Swiss explorer Johann Ludwig Burckhardt, travelling in disguise, brought it to European attention in 1812. UNESCO listed it in 1985.

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WonderOcean

Coral reefs cover less than 1 per cent of the ocean floor, yet they support about a quarter of all known marine species. They also shield coasts from storm waves.

A reef is built by coral polyps, tiny animals related to jellyfish that lay down skeletons of limestone. Most reef corals carry single-celled algae inside their tissue; the algae photosynthesise and pass food to the coral in return for shelter, and they also give it its colour. When the water stays too warm for too long, corals expel the algae and turn white, which is called bleaching; if the heat lasts, they starve and die. A global bleaching event from 2014 to 2017 hit about two-thirds of the world's reefs, and a fourth, from 2023 to 2025, the most severe on record, reached about 84 per cent of reef area.

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StillnessOcean

Mangroves, salt marshes and seagrass meadows draw carbon dioxide from the air and lock it away in waterlogged coastal mud, often for centuries. Scientists call this stored carbon 'blue carbon'.

The term was popularised by a 2009 United Nations report. Coastal mud holds so little oxygen that dead roots and leaves rot very slowly, so carbon keeps building up in the soil instead of returning to the air. These habitats cover only a small fraction of the seabed, yet they are thought to account for about half of all the carbon buried in ocean sediments. Mangroves also break waves, trap sediment and shelter young fish and crabs among their roots. When the wetlands are drained or cleared for shrimp farms or building, the stored carbon can escape back into the atmosphere.

Mangrove blue carbonRead card

WonderMigration

Every year more than a million wildebeest, joined by hundreds of thousands of zebras and gazelles, walk a great loop through Tanzania's Serengeti and Kenya's Maasai Mara, following the rains to fresh grass.

The herds have no fixed route; their path shifts each year with the rain. Early in the year hundreds of thousands of calves are born within a few weeks in the southern Serengeti. As the plains dry out the herds move north and west, reach Kenya's Mara in the middle of the year and return south when the short rains begin. The most dangerous moment is crossing the Mara River. A 2017 study found that on average about 6,250 wildebeest drown there each year, and their carcasses, some 1,100 tonnes, feed fish, crocodiles and vultures and fertilise the river for years. Grazing herds also keep the grasslands healthy.

Great wildebeest migrationRead card

WonderEvolution

In industrial Britain, the dark form of the peppered moth, first recorded in Manchester in 1848, became common where soot blackened the trees and hid it from birds. When the air was cleaned up in the twentieth century, the pale form returned.

The peppered moth became a textbook example of natural selection. By the 1890s nearly all peppered moths around Manchester were dark. In the 1950s Bernard Kettlewell's field experiments suggested that birds ate more of the moths that stood out against the bark, though critics later questioned his methods. After clean-air laws such as the UK's Clean Air Act of 1956 cut soot, the dark form became rare again. The geneticist Michael Majerus answered the critics with a six-year experiment in Cambridge involving 4,864 moths; published after his death, in 2012, it confirmed that birds took more of the conspicuous moths. In 2016 scientists traced the dark colour to a piece of mobile DNA inserted into a gene called cortex around 1819.

Peppered moth evolutionRead card

WonderArchitecture

Angkor, capital of the Khmer Empire in today's Cambodia from the ninth to the fifteenth century, was ringed by giant reservoirs, moats and canals that stored monsoon rain and moved water across an urban area of about 1,000 square kilometres.

The largest reservoirs, called barays, are vast rectangles banked with earth: the West Baray, built in the eleventh century, measures about eight kilometres by two and still holds water. Moats such as the one around Angkor Wat framed temples modelled on the sacred mountain and surrounding oceans of Hindu and Buddhist cosmology. Radar and aerial surveys published in 2007, and airborne laser scanning (lidar) that saw through the forest in 2012, revealed roads, canals and house mounds across at least 1,000 square kilometres, the largest known pre-industrial settlement. Researchers still debate how much the barays watered rice fields. Tree rings show long droughts broken by intense monsoons in the fourteenth and fifteenth centuries, which damaged the network and probably contributed to Angkor's decline.

Angkor hydraulic systemRead card

WonderArchitecture

The Alhambra, the hilltop palace and fortress of the Nasrid sultans of Granada in Spain, is threaded with channels, pools and fountains that cool its courtyards, mirror its buildings and water the Generalife gardens beside it.

The Nasrids, the last Muslim dynasty in Spain, ruled Granada from 1238 to 1492. Their founder, Muhammad I, began the palace complex, and water reached the dry hilltop through the Acequia Real, the Royal Channel, which draws on the Darro River several kilometres upstream and runs by gravity along the hillside. The Generalife, a summer palace with terraced gardens, was built in the early fourteenth century. In the Court of the Lions, from the later fourteenth century, twelve marble lions carry a fountain whose water runs out in four channels, echoing the Islamic image of paradise as a garden watered by four rivers. Some of the original channels still water the gardens today.

Alhambra and GeneralifeRead card

WonderOcean

Whales feed at depth and release nutrient-rich faeces near the surface, fertilising the phytoplankton, tiny drifting algae, at the base of the ocean food chain. Scientists call this the whale pump.

The term comes from a 2010 study by the marine scientists Joe Roman and James McCarthy, who looked at whales and seals in the Gulf of Maine, off the north-eastern United States. Many whales dive to feed and then rest and breathe at the surface, where they release loose, floating plumes of faeces rich in nitrogen. The researchers estimated that marine mammals return about 23,000 tonnes of nitrogen a year to the sunlit surface layer of the Gulf, more than all the rivers flowing into it combined, and that before industrial whaling the flow was probably much larger. Other studies found a similar effect with iron in the Southern Ocean. Because phytoplankton also absorb carbon dioxide, recovering whale numbers may help both ocean productivity and carbon uptake.

Whale pumpRead card

WonderTrade

The Incense Route carried frankincense and myrrh, fragrant tree resins, from southern Arabia to Mediterranean markets for centuries, through a chain of caravan towns, wells, forts and water systems across the desert.

Frankincense and myrrh come from trees that grow in the dry lands of southern Arabia and the Horn of Africa. They were burned in temples and homes, and used in medicine, perfume and embalming. Pliny the Elder, writing his Natural History around AD 77, says the road from Thomna in southern Arabia to Gaza on the Mediterranean was divided into 65 camel stages, and that by the coast each camel-load had cost 688 denarii in water, fodder, lodging, tolls and payments to priests, guards and officials. Cities that controlled parts of the route grew rich, among them Shabwa in Yemen and the Nabataean capital Petra in today's Jordan, whose cisterns and dams stored scarce rain for the caravans.

Incense RouteRead card

WonderMigration

Pronghorn from Grand Teton National Park travel up to about 240 km (150 miles) between their summer range and their winter range in Wyoming's Upper Green River Basin. Roads, fences and new building now cut across this ancient route.

Pronghorn look like antelopes but are the last surviving members of a family found only in North America. They can reach about 88 km/h, a speed beaten on land only by the cheetah, yet they rarely jump: faced with a fence, they look for a gap to crawl under, so tight wire fencing can block a route completely. At Trappers Point, a narrow bottleneck on the route, archaeologists found remains of pronghorn hunts about 6,000 years old. In 2008 the US Forest Service designated the Path of the Pronghorn, the first federally protected wildlife migration corridor in the United States. In 2012, overpasses and underpasses built on US Highway 191 near Pinedale gave the herds a safe way across the road.

Path of the PronghornRead card