READING PASSAGE 2
Ecosystems can fight back
A Conventional wisdom is often a poor guide. For one thing it suggests that human damage to the world's species, habitats and ecosystems is terminal: that when things are lost, they are lost for ever. But oil spills of the sort that now threaten the Timor Sea, forest fires like those that recently afflicted Greece, and other man-made and man-assisted threats to wildlife are transient. Except in those cases in which a species is driven to extinction, the Earth's ability to shrug such things off is often underestimated.
B Alan Weisman shows this in his book, "The World Without Us", which illustrates nature's great capacity to recover. Have mankind abducted by aliens or wiped out by some Homo sapiens-specific virus, and nature, Mr Weisman reckons, would reclaim its territory with surprising speed, as weeds colonised pavements, rivers flooded subway tunnels and buildings burst as they were played like concertinas by a cycle of freezing and thawing. By Mr Weisman's reckoning, residential neighbourhoods would return to forest in 500 years and only the most stubborn of human inventions, such as certain plastics, would prove permanent.
C Mr Weisman's conclusion was backed up earlier this year by a study published in the Public Library of Science by Holly Jones and Oswald Schmitz, of Yale's School of Forestry and Environmental Studies. They used Web of Science, an online journal archive, to gather a set of 240 peer-reviewed scientific papers that measured recovery rates in large terrestrial and aquatic ecosystems. The data thus available included work on agriculture, deforestation, the introduction of invasive species, logging, mining, oil spills, overfishing and the damage done to seabeds by trawling, as well as, for comparison, naturally occurring disasters such as hurricanes.
D The pair measured 94 aspects of how ecosystems are put together, including the ways in which nutrients cycle within them, the rates at which decomposition takes place and the sizes of their plant and animal populations, so that they could classify whether, and how fast, an area had recovered. They found that 83 of the 240 papers demonstrated complete recovery, while 90 showed a mixed response. Only 67 showed no recovery at all and, as the authors explain, more would have recovered if the projects had continued for long enough to track the changes in ecosystems that respond more slowly such as forests.
E Ecosystems exposed to more than one pressure, such as a forest that is first felled and then used for agriculture, took the longest to recover. Even in those cases, though, the average recovery time was, at 56 years, within a human lifetime. Sites that experienced single threats typically recovered in less than 20 years. The researchers found that recovery rates are influenced more by the type of ecosystem than by the magnitude of the damage inflicted upon it. Forests, for example, take longer to renew (42 years) than ocean floors (typically less than ten) regardless of the scale of the stresses inflicted on them.
F Some commentators are sceptical about such positive findings. They point out that, of necessity, the study's retrospective methodology includes papers published before researchers were required to declare any competing interests. This may have allowed, for example, an oil company to produce a report that plays down the damage done by a spillage. But such biased individual reports would be unlikely to affect the overall findings of a large study like this one.
G Critics also question whether total ecological recovery really has been achieved as often as Ms Jones and Dr Schmitz suggest, and point to examples where it manifestly has not, such as the cod fishery of the Grand
Banks, off the coast of Newfoundland, which collapsed in 1992. Almost two decades on, the cod show no sign of recovery, perhaps because new predators, such as dogfish, now dominate the waters.
H It is true, though, that the question of what is pristine or natural can be debatable. A good example of this, which Mr Weisman uses in his book, is Dartmoor, a national park in the south-west of England. Dartmoor is considered by many to be one of Britain's great nature wildernesses. In fact, it is a human construction, formed by tens of thousands of years' worth of alterations such as burning and agriculture. But it is in its current state, rather than as the forest it once was, that people wish to preserve it. Ms Jones and Dr Schmitz point out that most conservation work is not actually concerned with returning landscapes to their natural or prehuman states and "instead use contemporaneous reference systems as targets".
I Despite their study's limitations, and the difficulty of measuring recovery and choosing targets, Ms Jones's and Dr Schmitz's findings are good news for conservationists. But the final word of advice belongs to Mr Weisman as he invites people to ponder an alternative to his post-human future: "Since we're imagining, why not dream of a way for nature to prosper that doesn't depend on our demise?
READING PASSAGE 2
Poor countries have the world's worst environmental problems.
A "THE centralisation of population in great cities exercises of itself an unfavourable influence," wrote Friedrich Engels in 1844. "All putrefying vegetable and animal substances give off gases decidedly injurious to health, and if these gases have no free way of escape, they inevitably poison the atmosphere The poor are obliged to throw all offal and garbage, all dirty water, often all disgusting drainage and excrement into the streets, being without other means of disposing of them; they are thus compelled to infect the region of their own dwelling."
B Much of Engels's writing seems irrelevant today, but his description of working-class life in 19th-century London paints an uncannily accurate picture of slum life in developing countries at the end of the 20th century. In the Klong Toey district of Bangkok, the stench from the rotting rubbish and fetid water that collect between the shacks is overpowering. In the north of Mexico city, near Santa Fe, hovels cling to the sides of a steep valley which most days is choked with smog, and streams of untreated sewage run down to the river below. In the Moroccan town of Marrakesh, the smell of rotting cattle flesh surrounds tanneries for miles around.
C Conventional wisdom has it that concern for the environment is a luxury only the rich world can afford; that only people whose basic needs for food and shelter have been met (as well as, perhaps, some not-so-basic ones for things like cars and televisions) can start worrying about the health of the planet but surely developing countries, too, should be thinking about the environment. True, in the rich countries a strong environmental movement did not emerge until long after they had become industrialised, a stage that many developing countries have yet to reach. And true, many of the developed world's environmental concerns have little to do with immediate threats to its inhabitants' well-being. People worry about whether carbon-dioxide emissions might lead to a warmer climate next century, or whether genetically engineered crops might have unforeseen consequences for the ecosystem. That is why, when rich-world environmentalists campaign against pollution in poor countries, they are often accused of naivety. Such countries, the critics say, have more pressing concerns, such as getting their people out of poverty.
D The environmental problems that developing countries should worry about however are different from those that western pundits have fashionable arguments over. They are not about potential problems in the next century, but about indisputable harm being caused today by, above all, contaminated water and polluted air. Contrary to conventional wisdom, solving such problems need not hurt economic growth; indeed dealing with them now will generally be cheaper than leaving them to cause further harm.
E In most developing countries pollution seems to be getting worse, not better. Most big cities in Latin America, for example, are suffering rising levels of air pollution. Populations in poor countries are growing so fast that improvements in water supply have failed to keep up with the number of extra people. Worldwide, about a billion people still have no access to clean water, and water contaminated by sewage is estimated to kill some 2m children every year. Throughout Latin America, Asia and Africa, forests are disappearing, causing not just long-term concern about climate change but also immediate economic damage. Forest fires in Indonesia last year produced a huge blanket of smog that enveloped much of South-East Asia and kept the tourists away. It could happen again, and probably will.
F Recent research suggests that pollution in developing countries is far more than a minor irritation: it imposes a heavy economic cost. A World Bank study last year put the cost of air and water pollution in China at $54 billion a year, equivalent to an astonishing 8% of the country's GDP. Another study estimated the health costs of air pollution in Jakarta and Bangkok in the early 1990s at around 10% of these cities' income. These are no more than educated guesses, but whichever way the sums are done, the cost is not negligible.
G The growth in environmental problems in developing countries has been matched by a rise in local anxiety about them. In recent years hundreds of environmental lobby groups have sprung up in Latin America and Asia. Some of these are offshoots of rich-world groups such as Greenpeace, which now has offices in 11 developing countries. But many of the new groups are home-grown, drawing support from people increasingly worried about the effect of pollution on their health.
H In Bolivia, Mexico and Brazil, green activists have recently entered government. Bangkok's people, frustrated by the city's notorious congestion and pollution, have elected a governor with strong green credentials, Bichit Ratanakorn, who has threatened to "name and shame" firms that flout pollution rules. He is urging other Asian cities at an earlier stage of industrialisation "not to follow in our footsteps".
I From Brazil to China, governments are passing increasingly tough environmental regulations, many of them modelled on green standards in Europe and North America. Often this is an empty gesture: many countries are unwilling or unable to enforce green regulations. Brazilian politicians may have felt a warm glow in January when they passed a law against "environmental crimes", but Brazil already has legislation prohibiting Amazon landowners from deforesting more than 20% of their land. That has done nothing to stop many of them cutting down all their trees.
READING PASSAGE 3
Questions 27 - 40
Climate change and the Atlantic
Are changes in ocean circulation about to turn our lives upside down, or is this something only our grandchildren will have to cope with? This vital question is in doubt because the behaviour of ocean currents is still remarkably obscure. On a crude level, the oceans of the world are linked together by a network of currents sometimes called the global conveyor, with warm surface flows connecting to cold deep currents. The conveyor is driven by winds and by a more complicated process called thermohaline circulation - and this is the process that has climatologists worried.
As its name implies, thermohaline circulation depends on heat and salt. An offshoot of the Gulf Stream called the North Atlantic Drift flows all the way to the seas off Greenland and Norway. Evaporation makes the water saltier, so as it is chilled by Arctic winds it becomes denser than the waters underneath it and sinks. It then spills back southward over the undersea ledges between Greenland and Scotland to form a slow, cold, undersea river called the North Atlantic Deep Water. This flows all the way to the Southern Ocean, with some water going as far the Indian Ocean, where it gradually wells up again, perhaps a millennium after it sank.
The weak link is the sinking process. Climate change is injecting ever more fresh water into the Arctic by increasing river flows and accelerating the calving of icebergs from Greenland. This fresh water dilutes the North Atlantic Drift, reducing its density and making it more buoyant. If the fresh water input reaches a critical rate, around 100,000 tonnes per second, sinking could stop entirely. The northern branch of the conveyor would stop, and warm tropical waters would no longer flow past the west coast of Europe.
With that million-gigawatt heat supply switched off, climate models suggest that air temperatures in the region could fall by between 5 and 10 °C, and parts of the US and Canada would suffer too. A switch-off like this is blamed for a cold snap 12,000 years ago called the Younger Dryas, which turned the forests of Scandinavia into tundra. Could it be happening again? That spectre was raised in December by Harry Bryden of the National Oceanography Centre in Southampton, UK. His team took a ship from Florida to the coast of North Africa, stopping at 120 points en route to lower a bundle of instruments all the way to the sea floor. The researchers compared their results with similar measurements made at irregular intervals since 1957. According to their analysis, the deep, cold return leg of the circulation has weakened by 30 per cent. If that has slowed, they reasoned, then the northward branch of warm water must have slowed too.
In fact, the slowdown seems to have started nearly a decade ago. When the US National Oceanic & Atmospheric Administration made a similar survey of the Atlantic in 1998 it was interested in carbon dioxide levels and did not calculate the flow rate. When Bryden's team did the sums, they found the flow had been relatively steady between 1957 and 1992, dropped off by 1998 and remained low. Bryden's paper prompted some nervous press coverage. "There were alarming stories saying that the sky is falling," says Carl Wunsch, a physical oceanographer at Massachusetts Institute of Technology. "It's a complicated story reduced to a fairytale". In fact, Bryden's measurements are not proof of imminent cataclysm.
One question mark is whether his team has simply seen short-term fluctuations in the ocean. "The ocean is a very turbulent beast. We tend to assume that at great depth it is quiet, but that's not necessarily so," says Stefan Rahmstorf of the University of Potsdam in Germany. Wunsch likens it to the vagaries of the weather: "It might get colder for a few days in England, but you don't necessarily say we're entering a new ice age."
Bryden, however, thinks his team has found more than a stutter. "If we just had the 1998 data we'd be nervous, but 2004 is similar to 1998," he says.
There are other reasons to be cautious. Climate models do not predict any substantial slowdown in Atlantic currents until near the end of this century. "It would mean all our models are wrong," says Rahmstorf. Bryden thinks they might well be: "I think if we measure a slowdown, the models will follow."
The trouble for Bryden is that not all observations fit in with his conclusions. If less warm water is flowing north, the seas off western Europe ought to be cooler than normal. They are not. In fact, these waters are slightly warmer than a decade ago. And direct measurements of the cold, deep currents that spill southwards over the ledges joining Scotland, Iceland and Greenland do not show a downward trend. Although these currents did slow between 1995 and 2000, they have picked up again. "We are faced with conflicting evidence," says Rahmstorf.
How to resolve this conflict? It is possible that Bryden's group has got its physics wrong. Like other groups, the team did not measure flow rates directly, but instead calculated them from measurements of temperature and salinity. Rahmstorf and Wunsch both point out that these calculations rely on assumptions that are far from proven.
Alternatively, it could be that the currents are changing in ways that no one has anticipated. There is a vast stretch of ocean between Bryden's measurements at 25° north and the overspill at around 65°. In between, the warm surface current becomes meandering and unstable, and difficult to measure, says oceanographer Tore Furevik of the University of Bergen in Norway. "There are certainly large changes going on beneath the surface of the North Atlantic, but we are still missing too many pieces in the puzzle to get the picture clear," he says.
For the moment, this rather unsatisfactory answer is the best we have. Oceanographers and climate scientists agree that thermohaline circulation will slow as the world warms, but most think it will happen later rather than sooner. In its report due next year, the Intergovernmental Panel on Climate Change is likely to predict a slowdown of at most 50 per cent by the end of this century.