IELTS Academic Reading full test 1

Cooling the city

A On a hot summer afternoon, the centre of a large city can be several degrees warmer than the farmland around it. This effect, known as the urban heat island, occurs because roads, roofs and buildings absorb heat during the day and release it slowly at night. Cities also have fewer trees and less open soil, so there is less evaporation to cool the air.

B Researchers now use satellite images to map surface temperatures across entire cities. These maps often reveal striking differences between neighbourhoods: leafy suburbs may be far cooler than nearby areas dominated by car parks and warehouses. Such data allow councils to identify the streets where intervention is most urgent.

C One of the most effective responses is to copy what forests do naturally. Trees provide shade and release water vapour through their leaves, a process that can cool the surrounding air. Green roofs and walls, covered with plants, work in a similar way, while also reducing the amount of rainwater that rushes into drains during storms.

D The benefits of cooler streets are not shared equally. Older people, young children and those with existing health conditions are most at risk during heatwaves, and lower-income areas often have the least tree cover. For this reason, some cities now prioritise planting in disadvantaged neighbourhoods.

E Failing to act is expensive. Heatwaves increase hospital admissions, reduce productivity among outdoor workers and push up electricity demand as residents run air-conditioners. Economists estimate that, over time, the cost of these effects can be far greater than the cost of planting and maintaining trees.

Why teenagers can't get up in the morning

A Parents have long complained that teenagers stay up late and are impossible to wake in the morning. For many years this was put down to poor habits, late-night screens or simple laziness. Sleep researchers now believe that something more fundamental is going on: during adolescence, the body clock itself shifts later.

B The timing of sleep is controlled partly by melatonin, a hormone released by the brain as evening approaches. In young children, melatonin levels rise early in the evening. Studies that measured the hormone in saliva found that, in teenagers, the rise happens up to two hours later. As a result, a fifteen-year-old who goes to bed at ten o'clock may simply lie awake, not because they are unwilling to sleep but because their body is not yet ready.

C At the same time, the need for sleep does not fall during the teenage years. Most experts recommend between eight and ten hours a night for this age group. When early school start times are combined with a late body clock, the result is a large and regular shortfall. Surveys in several countries suggest that a majority of secondary students get less than eight hours on school nights, and many try to 'catch up' by sleeping late at weekends, which can push their body clock even later.

D The consequences go beyond tiredness. Teenagers who are short of sleep tend to find it harder to concentrate and remember new information, and some research links lack of sleep with low mood and a greater risk of accidents among young drivers. One researcher, Dr Helen Marsh, has described chronic sleep loss in adolescents as 'a public health issue hiding in plain sight'.

E A number of school districts have experimented with later start times. In one widely reported trial in the United States, secondary schools moved the start of the school day from 7.50 am to 8.45 am. Students' average sleep increased by around forty minutes a night, attendance improved and fewer students reported falling asleep in class. Similar trials elsewhere have produced more modest results, partly because some students used the extra time to go to bed later.

F Changing school timetables is not straightforward. Later finishing times can clash with sport, part-time work and family routines, and bus services may need to be reorganised. Some researchers therefore argue that schools should combine later starts with education about sleep, for example encouraging students to keep regular hours at weekends and to reduce bright light from screens late in the evening.

Gardening under the sea

Coral reefs cover less than one per cent of the ocean floor, yet they support around a quarter of all marine species. They also protect coastlines from waves and provide food and income for hundreds of millions of people. Over recent decades, however, many reefs have been damaged by rising sea temperatures, pollution and storms. When water becomes too warm, corals expel the tiny algae that live inside them and give them their colour. This process, known as bleaching, does not kill the coral immediately, but if high temperatures continue for several weeks, the coral may starve.

In response, scientists and volunteers have begun to restore reefs in much the same way that foresters replant trees. The most common method is 'coral gardening'. Small fragments of healthy coral are attached to underwater frames or ropes, where they grow in nurseries for between six and twelve months. They are then fixed onto damaged parts of the reef using cement or cable ties. Marine biologist Dr Rafael Ortiz, who has run nurseries in the Caribbean for fifteen years, says that well-managed nurseries can grow fragments several times faster than corals grow in the wild.

Other teams are experimenting with different approaches. In Australia, researchers led by Professor Amy Chen collect coral spawn, the eggs and sperm released by corals during a few nights each year, and raise millions of baby corals in floating pools before releasing them onto damaged reefs. Professor Chen points out that this method allows restoration at a much larger scale than planting fragments by hand. Meanwhile, engineers in Indonesia have installed thousands of steel structures, nicknamed 'reef stars', which provide a stable base on loose rubble where young coral would otherwise be swept away.

Some scientists are trying to help corals cope with future conditions. Dr Kofi Mensah's laboratory breeds corals from colonies that survived previous heatwaves, in the hope that their offspring will be more heat-tolerant. Dr Mensah stresses, though, that such 'assisted evolution' is still at an early stage and that the long-term effects on reef ecosystems are not yet understood.

Restoration has clear limits. Even the largest projects cover only a few hectares, while the reefs being lost are measured in thousands of square kilometres. Restored areas can also be destroyed by a single severe heatwave. For this reason, most experts agree that restoration must go hand in hand with reducing greenhouse gas emissions and improving water quality. As Dr Ortiz puts it, 'Restoration buys time. It does not solve the problem.'