Reading 2 — the urban heat island
A second full-length Academic Reading passage, this one from environmental science: why a city is warmer than the country around it, why the gap is biggest at night, and what can be done about it. Seven lettered paragraphs, thirteen questions, and the academic vocabulary of the text on flashcards.
The structure is the one Academic passages use most often — a phenomenon, its causes, a complication, its consequences, and what follows — and it rewards a particular reading habit. The causes are numbered in the text ("the first… the second… the third"), and several questions turn on keeping them apart: the question about a paved surface after rain is about the third mechanism, and a plausible answer drawn from the second is wrong.
Two questions are about what the writer does not say. One statement is never made anywhere — that Luke Howard's measurements were later shown to be inaccurate — and the passage neither supports it nor denies it; it simply never raises the question, which is exactly what Not Given means. Another is contradicted, and the passage takes the trouble to contradict it twice, at the start of one paragraph and again in the next: waste heat from machines is not the main cause. When a text denies something that firmly, it is usually because the writer expects you to assume the opposite.
The rest run through headings, detail, purpose (why sweat is mentioned in a paragraph about physics), the writer's view of air conditioning, and an abstract word explained by the clause beside it.
Written by Zestly. No IELTS material is reproduced.
- Keep numbered causes apart when the wrong option comes from the neighbouring one
- Recognise a statement the text neither supports nor denies
- Spot a claim the writer contradicts, and notice when it is contradicted twice
- Read a writer's view that criticises something without proposing to ban it
- Build the academic vocabulary of cause, measurement and remedy
Three properties of a city account for most of the effect, and none of them is heat from machines. The first is the surface itself: asphalt and dark roofing absorb a large share of the sunlight that falls on them, where a field or a pale wall would reflect more of it away.
Sample question
Reading Passage — Why a city does not cool down at night A Anyone who has walked out of a city on a summer evening has felt it: the air cools as the buildings thin out. The difference is measurable and it has a name. An urban heat island is the warmth of a built-up area relative to the countryside around it, and the first person to document one was a London chemist, Luke Howard, who from 1818 published years of paired readings taken inside the city and beyond it. London, he found, was consistently the warmer of the two — by something under a degree on average, and by considerably more on some nights. B Three properties of a city account for most of the effect, and none of them is heat from machines. The first is the surface itself: asphalt and dark roofing absorb a large share of the sunlight that falls on them, where a field or a pale wall would reflect more of it away. The second is the mass of the material. Brick, concrete and stone store what they absorb and give it back slowly, so a city is still releasing the previous afternoon long after sunset. The third is the absence of water. In the countryside a great deal of the sun's energy goes into evaporating moisture from soil and leaves, a process that cools the surface as surely as sweat cools skin; a paved catchment sheds rain into a drain within minutes and has nothing left to evaporate. C A fourth factor is geometry rather than material. A narrow street between tall buildings is a poor radiator: heat leaving one wall is intercepted by the wall opposite instead of escaping to the sky. The measure climatologists use for this is the sky view factor — the fraction of the sky visible from a point on the ground — and it falls as streets grow narrower and buildings taller. Waste heat from vehicles, industry and cooling equipment adds to the total, and in a dense business district on a hot afternoon it is not trivial, but across a whole city it is the smaller contribution. D The effect is not constant, and the moments when it is largest are not the ones most people expect. A heat island is usually weakest in the middle of a summer afternoon, when the sun is heating city and country alike, and strongest a few hours after sunset, when open ground has cooled quickly and the city has not. It is also strongest on clear, calm nights: cloud slows the escape of heat from the countryside as well, and wind mixes urban and rural air, so both flatten the difference. That is why the phenomenon is described in terms of the night-time minimum rather than the daytime maximum. E Comparing a city with its surroundings is harder than it sounds. A thermometer in a car park reads differently from one on grass fifty metres away, and the standard rural reference site may be an airport, which is itself a large expanse of asphalt. Satellites measure the temperature of surfaces rather than of the air a person breathes, and on a sunny day the two can differ by many degrees. Careful studies therefore use fixed networks of identical instruments, or a vehicle driven along the same route at the same hour — a modern version of what Howard did on foot. F What follows from a few degrees is mostly a matter of health. Heat kills through the cumulative strain of days and, above all, of nights that do not cool; a body that cannot recover overnight starts the next day already depleted, and the people least able to leave are usually the ones living in the warmest streets. Cooling equipment is the obvious individual response and the worst collective one, since it moves heat from inside buildings into the street and consumes the electricity that cities are least able to supply on exactly the days it is wanted. G Most of the remedies reverse one of the causes rather than adding anything new. Pale roofs and paving reflect the sunlight that dark ones absorb. Street trees shade the surfaces beneath them and return water to the air through their leaves, doing the work of the first and third mechanisms at once. Permeable surfaces and planted roofs restore some of the moisture that drainage takes away. None of it is quick — a street tree is an investment in a decade's time — and none of it alters the fact that a city is built of the materials a city is built of. — Which heading best fits Paragraph D?
- When the difference is at its biggest
- The trouble with choosing a place to compare
- Reversing the causes, one at a time
- What a narrow street does to escaping heat
See the answer
When the difference is at its biggest
Paragraph D is about timing throughout: weakest in the middle of a summer afternoon, strongest "a few hours after sunset", and strongest again "on clear, calm nights". The other three headings summarise Paragraphs E, G and C — all true of this text, none of them true of Paragraph D.