IELTS Academic Reading — Practice Test 11

On a still summer night, a city can be several degrees warmer than the farmland that surrounds it. This difference, known as the urban heat island, has been measured in settlements of every size, and in the largest cities the gap between the built-up core and the open countryside can reach eight degrees Celsius or more after dark. The effect is not simply a curiosity for meteorologists. As heatwaves grow more frequent and more intense, the extra warmth trapped in cities is turning from a discomfort into a genuine hazard, one that falls hardest on the old, the sick and the poor. With more than half of humanity now living in urban areas, and that share still rising, the number of people exposed to this additional heat is climbing year by year.

Several mechanisms combine to produce the effect, but the behaviour of urban surfaces is the most important. Asphalt roads and dark roofs absorb a large share of the sunlight that strikes them, whereas fields and forests reflect more of it and use much of the rest to evaporate water from soil and leaves. The concrete, brick and stone from which cities are built also store heat efficiently, soaking it up through the day and releasing it slowly long after sunset. Add to this the heat vented directly by vehicles, factories and, above all, air-conditioning units — which cool the indoors by pumping warmth outdoors — and the recipe for a hotter city is complete.

It is at night that the urban heat island does its real damage. During the day, cities are not always dramatically hotter than their surroundings, but after sunset the countryside cools quickly while the city, still radiating the day's stored heat, does not. The human body relies on cooler nights to recover from daytime heat, and when that relief never comes the strain on the heart and circulation accumulates. Studies of heatwaves have repeatedly found that deaths rise most steeply where nighttime temperatures stay high, which is precisely the condition the urban heat island creates. A single scorching afternoon is survivable for most people; it is the run of sweltering nights, one after another, that overwhelms the body's defences and fills hospital wards.

What is less widely appreciated is how unevenly the heat is distributed within a single city. Detailed temperature surveys have shown that the hottest districts are often the poorest, precisely because they contain the fewest trees, the least parkland and the most unbroken expanses of paving. Wealthier neighbourhoods, with their gardens and tree-lined streets, can be markedly cooler than districts only a short distance away. The pattern is no accident; it frequently mirrors decades-old decisions about where to plant, where to build and whom to house. The heat island, in other words, is as much a social map as a physical one.

The remedies fall into two broad families, each with its drawbacks. The first is to change the surfaces themselves. Painting roofs white, or coating them with reflective materials, can lower the temperature of a building and the air around it substantially, and because the technique is cheap it has been adopted enthusiastically in some hot cities. Yet reflective roofs are not an unqualified good. In cities with cold winters, a roof that rejects the sun's warmth in July also rejects it in January, raising heating bills; and a landscape of brilliant white surfaces can create glare and bounce heat towards pedestrians walking at street level, where it is least welcome.

The second family of remedies works with vegetation rather than against the sun. Trees cool their surroundings twice over: they shade the ground from direct sunlight, and they release water vapour from their leaves, a process that absorbs heat much as sweating cools the skin. A mature street tree can make a genuine difference to the temperature of the pavement beneath it. But trees are not a costless solution either. They take years to grow, they demand water that dry cities can ill afford, and they require long-term maintenance that hard-pressed municipal budgets often fail to provide.

No single measure will tame the urban heat island, and treating it as a technical problem with a technical fix misses the larger picture. The warming of cities is bound up with how they are planned, who lives where, and how much energy their inhabitants consume — and all of this is unfolding against the background of a climate that is itself growing hotter. The most successful responses so far have combined reflective surfaces, expanded greenery and tighter building rules, applied street by street rather than imposed from above. Crucially, they have directed the greatest effort towards the districts that suffer most, rather than spreading resources thinly and evenly. The heat island cannot be abolished, but it can be made less dangerous.

For most of the history of medicine, doctors had little to offer but their manner and a handful of remedies that, we now know, did nothing at all. That patients so often recovered anyway was long treated as an embarrassment — evidence, at best, of the body's capacity to heal itself. Only in the twentieth century did researchers begin to take seriously the possibility that the treatment itself, however inert, might be doing something. The placebo effect, as it came to be called, describes a measurable improvement in a patient's condition following a treatment that has no active ingredient: a sugar pill, an injection of salt water, a procedure performed for show. What had been a nuisance to be explained away became a phenomenon to be studied in its own right.

The first thing to be established was that the effect was not merely a matter of patients being polite or imagining their recovery. Careful experiments have shown genuine physiological changes: measurable falls in blood pressure, the release of the body's own painkillers, shifts in the activity of the brain regions that process discomfort. Yet demonstrating this is harder than it sounds. A patient given a dummy pill may improve for reasons that have nothing to do with the pill — the illness may simply have run its course, or an unusually severe bout may have been followed, as such bouts tend to be, by a return to something nearer the average. Separating a true placebo response from these ordinary patterns of recovery is one of the central difficulties of the field.

Where the effect is real, two mechanisms appear to be at work. The first is expectation: a patient who believes a treatment will help releases, in anticipation of relief, some of the same chemicals that an effective drug would trigger. Studies of pain have shown that this response can be blocked by a substance that interferes with the body's natural opioids, strong evidence that the brain is medicating itself. The second mechanism is conditioning, the same process by which a dog learns to salivate at a bell. A patient who has repeatedly felt better after taking a real drug may come to respond to the mere act of taking a pill, even an empty one, much as the body of a person who has often eaten at a certain hour begins to prepare for food before any arrives.

It matters, though, to be clear about what the placebo can and cannot do. Its power is greatest over symptoms that the brain itself generates or regulates — pain, nausea, fatigue, anxiety, the low mood of depression. It has little or no effect on the underlying course of most diseases: a placebo will not shrink a tumour, mend a broken bone or clear an infection. This distinction is easily blurred. A patient with cancer who feels less pain after a placebo has been genuinely helped, but the cancer itself is untouched. Confusing relief of symptoms with cure has led to a great deal of dangerous nonsense, and to the marketing of worthless treatments that work, insofar as they work at all, entirely through expectation.

Some researchers go further, and question whether the effect is as large or as common as enthusiasts claim. In an influential review published in 2001, two Danish scientists gathered the trials in which patients had been assigned either to a placebo or to no treatment at all, and concluded that, for most conditions, the placebo groups did little better than those left untreated. The apparent power of placebos, they argued, had been inflated by the very statistical patterns — natural recovery, the tendency of extremes to moderate — that this article has already described. Their critics replied that the review had lumped together too many different conditions to be meaningful, and that for pain in particular the placebo effect remained robust. The dispute has not been settled, and it serves as a caution against the more extravagant claims made on the placebo's behalf.

If placebos work partly through belief, an obvious objection follows: to prescribe one, a doctor must deceive the patient, and deception sits uneasily with the trust on which medicine depends. For a long time this seemed an insurmountable barrier to using placebos openly. Then came a genuinely surprising finding. In several studies, patients who were told plainly that they were receiving a pill with no active ingredient nonetheless reported improvement in conditions such as chronic back pain and irritable bowel syndrome. Quite how an 'open-label' placebo can work, when the supposed mechanism of belief has been removed, is not understood. It may be that the ritual of treatment — the consultation, the act of taking something, the sense of being cared for — carries an effect of its own, independent of any specific expectation.

That possibility points to the deepest lesson of placebo research, which is not really about sugar pills at all. Every treatment, however powerful its active ingredient, is delivered inside a context — the reputation of the drug, the confidence of the doctor, the atmosphere of the clinic — and that context shapes the outcome. The placebo effect is simply the part of healing that this context contributes, laid bare by stripping the active ingredient away. Understood in this way, it is not a curiosity at the margins of medicine but a component of every encounter between healer and patient. To dismiss it is to discard something that, used honestly, might make real treatments work better.