Matching features

Reading Passage 2 – Farming Upwards

A The idea sounds like science fiction: lettuces, herbs and strawberries growing in tall stacks inside a windowless warehouse, bathed in pink and blue light, without a single grain of soil. Yet over the past fifteen years, so-called vertical farms have moved from architectural drawings to commercial reality. Their supporters present them as an answer to some of the most pressing problems in agriculture, from water shortages to the long supply chains that bring food into cities. The industry's record, however, has been decidedly uneven: alongside a number of thriving operations, there have been several expensive and highly publicised failures.

B The basic technology is not complicated. In most vertical farms, plants are grown hydroponically, with their roots suspended in a solution of water and dissolved nutrients; in some, the roots hang in the air and are sprayed with a fine mist, a method known as aeroponics. Because the water is collected and recycled, operators claim that they use up to 95 per cent less than a conventional farm growing the same crop. The buildings are sealed, so pests have difficulty getting in, and pesticides are rarely needed. Light comes from LED lamps, and according to the plant scientist Professor Ines Duarte, this is where much of the sophistication lies. 'Plants don't use all colours of light equally,' she explains. 'With LEDs we can adjust the spectrum to whatever a particular species needs at each stage of its growth, which is something the sun obviously can't offer.'

C For retailers, however, the main attraction is not efficiency but freshness. A lettuce grown in a field may spend several days in lorries and warehouses before it reaches a shop, losing flavour and shelf life on the way. A vertical farm can be built on the edge of a city, or even inside it, so that produce harvested in the morning can be on supermarket shelves the same day. 'Our customers aren't paying for technology,' says Marcus Feld, who founded one of the first commercial vertical farms in northern Europe. 'They're paying for a salad that lasts a week in the fridge instead of three days.' Production is also predictable: an indoor farm is unaffected by drought, flood or an unexpected frost, and can deliver the same quantity every week of the year.

D The difficulty is energy. Sunlight is free; electricity is not. Every hour of light that a plant receives indoors has to be paid for, and so does the cooling needed to remove the heat that the lamps produce. This explains why vertical farms grow almost nothing but leafy greens, herbs and a few soft fruits. These crops grow quickly, are harvested whole and sell for a relatively high price per kilogram. Staple crops such as wheat and rice are a different matter. The agricultural economist Dr Hannah Kessler has calculated that the electricity required to produce a single loaf's worth of wheat indoors would cost many times the price of the loaf itself. 'The question for any crop is simply how much money each unit of light can earn,' she says. 'For basil, the answer is: quite a lot. For grain, it's almost nothing.'

E This arithmetic became painfully clear when energy prices rose sharply in the early 2020s. Several well-funded companies, some of which had raised hundreds of millions of dollars from investors, were forced to close farms or declare bankruptcy. In many cases, critics argued, the business plans had been based on optimistic assumptions about costs and on the belief that rapid expansion would bring economies of scale. Feld is candid about the mistakes. 'Frankly, many of us built for a world of cheap electricity,' he admits. 'When that world disappeared, the numbers stopped working.'

F Few observers now believe that vertical farming will replace conventional agriculture, but that does not mean it has no future. Some growers are combining the two approaches, using greenhouses that take advantage of natural daylight and switch on LEDs only when the sun is weak. Others are powering their farms with solar or wind energy, or using waste heat from nearby factories. Duarte believes that the technology's greatest value may lie elsewhere altogether. 'Think of research stations in Antarctica, desert cities, or one day a base on the Moon,' she says. 'Where you can't farm at all, a vertical farm doesn't have to compete with a field. It only has to work.'

Reading Passage 2 – Second Lives Beneath the Waves

A When a ship reaches the end of its working life, it is usually towed to a breaker's yard, where it is cut up and its steel sold for scrap. A small number, however, meet a very different fate. Cleaned, stripped and then deliberately sunk, they come to rest on the seabed, where within months they begin to attract fish, corals and sponges. Artificial reefs of this kind have been created off the coasts of the United States, Australia, Malta and many other countries, and they have become popular destinations for divers. But the practice has always had its critics, and the question of whether a sunken ship is a gift to the ocean or simply a convenient way to dispose of waste has never been entirely settled.

B The idea of placing objects in the sea to attract fish is far from new. Fishermen in Japan were sinking wooden frames weighted with stones in the eighteenth century, and similar practices have been recorded in the Mediterranean. What has changed is the scale. In the second half of the twentieth century, governments began to sink not only ships but also old railway carriages, military vehicles and even concrete from demolished buildings. Some of these early projects were poorly planned: in one notorious case off the coast of Florida, around two million used car tyres were bound together and dropped into the sea in the 1970s, in the hope that they would become a reef. Instead, the bundles broke apart in storms, and loose tyres were thrown against existing natural reefs, damaging them. Clearing them up has cost millions of dollars.

C Lessons from such failures have shaped modern practice. Before a ship can be sunk today, it must be thoroughly cleaned of fuel, oil, paint containing toxic substances, and any loose material that could float away. Wiring and insulation, which may contain harmful chemicals, are removed, and openings are cut in the hull so that divers can enter and leave safely. This preparation is expensive and can take more than a year; in some cases it costs more than the value of the scrap metal the ship would otherwise have produced.

D Why do marine organisms colonise a wreck so quickly? Part of the answer is that, on much of the seabed, hard surfaces are scarce. Many coastal waters have floors of sand or mud, to which corals and sponges cannot attach themselves. A ship provides a large, stable structure rising from the seabed, with sheltered spaces of every size, from narrow gaps between metal plates to entire rooms. Small fish shelter in these spaces, and larger predators follow them. Biologist Elena Marsh, who has surveyed wrecks in the Gulf of Mexico for over a decade, has found that the number of fish around a ship can exceed that on a natural reef of similar size within five years.

E Not everyone is convinced that this represents a real benefit. A central question, raised by the fisheries scientist Tom Akers among others, is whether artificial reefs actually produce new fish or merely attract existing ones from the surrounding area. If the latter is true, a wreck may do more harm than good, because concentrating fish in one place makes them easier for fishing boats to catch. Akers argues that the answer probably varies from one species to another, and that without careful long-term monitoring it is impossible to know which effect dominates in any particular case.

F There are also concerns about what happens as a wreck ages. Steel corrodes in seawater, and while a large ship may remain structurally sound for many decades, its upper decks will eventually collapse. The engineer Rosa Lindqvist points out that the rate of corrosion depends heavily on depth and water temperature, and that ships sunk in shallow, warm waters may deteriorate much faster than their planners expected. As the structure breaks down, the habitat it provides changes too, and divers who enter older wrecks face increasing risks.

G Supporters respond that, whatever its effect on fish numbers, a well-managed artificial reef can relieve pressure on natural ones. Popular natural reefs suffer damage from the anchors and fins of large numbers of visiting divers. By offering an attractive alternative nearby, a sunken ship can draw some of these visitors away. The marine economist David Okoro has calculated that a single wreck off the coast of South Australia generates several million dollars a year in tourism, much of it for small businesses such as dive schools and guesthouses. For coastal communities, he suggests, this income may matter as much as any ecological argument.

Reading Passage 2 – Keeping the Same Time

A Before the nineteenth century, few people had any reason to know what time it was anywhere other than in their own town. Time was local: noon was the moment when the sun stood highest in the sky, and because the sun appears to travel from east to west, noon arrived a little later at every place further to the west. A town a hundred kilometres west of another would therefore keep time several minutes behind it. Public clocks on churches and town halls were set by sundials or by astronomical observation, and nobody was troubled by the fact that neighbouring towns disagreed.

B The railways changed this. When journeys that had once taken days could be completed in a few hours, differences of a few minutes began to matter. A passenger reading a timetable needed to know whether a departure time referred to the clock at the station he was leaving or at the one he was travelling to, and staff scheduling trains on a shared line needed a single reference if collisions were to be avoided. In Britain, individual railway companies began to run their trains according to London time, and within little more than a decade most of the country's railways had adopted it.

C This so-called railway time did not win immediate acceptance. Many towns continued to keep their own local time on public clocks, and some clocks were fitted with two minute hands, one showing local time and the other railway time. Critics complained that an arrangement designed for the convenience of commercial companies was being imposed on everyone else. Nevertheless, the practical advantages proved hard to resist, and over the following decades the great majority of public clocks came into line. Parliament finally made Greenwich Mean Time the legal time throughout Great Britain in 1880.

D In North America, the problem was far greater. The continent was so wide that a single national time was impossible, and before the 1880s the railroads operated on dozens of different times, often each company's own. On 18 November 1883, the railroads of the United States and Canada introduced a system of standard time zones, each covering a broad band of territory and differing from its neighbours by exactly one hour. In many places, the change took effect at midday, and the occasion became known as 'the day of two noons', because in towns that had to turn their clocks back, noon arrived twice. Remarkably, the new zones had no legal basis in the United States until 1918; for more than three decades, they were simply an agreement among private companies.

E Meanwhile, astronomers and geographers were debating a related question: from which line of longitude should the world measure east and west? Different nations used their own capitals or observatories as the starting point on their maps and charts, which caused confusion for navigators. In 1884, delegates from more than twenty countries met at a conference in Washington, D.C., and voted to adopt the meridian passing through Greenwich, in London, as the world's prime meridian. One reason for the choice was practical: a large majority of the world's shipping already used charts based on Greenwich. Not every country accepted the decision at once, however; France, for example, continued to use the Paris meridian for many years afterwards.

F The conference did not establish a worldwide system of time zones, but it prepared the ground for one. Over the following decades, country after country adopted a standard time defined in relation to Greenwich, most commonly a whole number of hours ahead of it or behind it, although a few chose offsets that include an extra half hour or even three-quarters of an hour. In practice, zone boundaries rarely follow lines of longitude exactly; they bend around national and regional borders, and some large countries have chosen to use a single time across their entire territory.

G Today, the precise time is no longer set by the sun, or even by an observatory at Greenwich. Since the 1960s, the second has been defined by the vibrations of atoms, and the world's official time scale, Coordinated Universal Time, is maintained by combining the readings of hundreds of atomic clocks in laboratories around the world. Yet the basic idea remains the one that the railways made necessary: people in widely separated places agreeing to read the same hour from their clocks. It is easy to forget how recent that agreement is, and how much argument it took to reach it.