Cooling the Earth - Test 1

C2 Proficiency · Gapped Text · Cambridge English Proficiency 1, Cambridge University Press

You are going to read an article about ways of combating global warming. Seven paragraphs have been removed from the article. Choose from the paragraphs A–H the one which fits each gap (1–7). There is one extra paragraph which you do not need to use.

Cooling the Earth

As a last resort to combat global warming, researchers are investigating two possible ways of applying 'sunscreen' to the planet.

The idea is to manufacture discs of silicon about 60 centimetres across. Each disc would be studded with holes of precisely calculated sizes, close to the wavelengths of visible light, which would scatter incoming light like a lens. The effect would be to produce a slight but imperceptible dimming of sunlight.

So, is the concept of a technological fix new? Not at all; but while most remedies have focused on combating greenhouse gases themselves – finding ways to remove them from the air or scrub them from power-plant emissions – only recently have more radical ideas been taken seriously.

Well, fortunately, if the worst comes to the worst, scientists still have a few tricks up their sleeves. For the most part they have strongly resisted discussing these options for fear of inviting a sense of complacency that might thwart efforts to tackle the root of the problem. Until now, that is.

What's more, geo-engineering in general has major drawbacks. It does nothing about the carbon dioxide in the atmosphere, which would still produce effects such as ocean acidification. When carbonic acid runs into the oceans from rocks, they get more acidic. Nobody disputes that this will happen on an increasing scale. The only question is how much it matters to basic ecosystems.

The simplest method put forward has been known for decades. That is to inject sulphur dioxide into the stratosphere, mimicking the cooling effects of volcanoes. Sulphur is cheap, and the means of releasing it could be as simple as pumping it up through a vertical pipe as much as ten kilometres long. Sulphur dioxide forms sulphate particles that are big enough to block part of the incoming sunlight, but small enough to allow infrared wavelengths – the heat radiation from the Earth – to escape back into space.

So, which approach has the edge? It comes down to costs and feasibility. If we were suddenly faced with a climate catastrophe, the sulphur-particle approach is cheap enough to be essentially free. The engineering is simple enough that it could be put up in a couple of years. The space sunshade, though attractive, seems unlikely to be implemented. If cost were no object, one would want to use something like this latter scheme, because it's very clean and controllable, and would likely minimise any secondary effects. But it's very expensive. If you want to go to that much effort, it would be simpler just to change our energy systems.

The approach is not without side-effects, however. Anything we do within the Earth's atmosphere might have unpredictable results that turn out to be worse than the cure, such as dramatic changes in regional rainfall or drought patterns, or chemical reactions that might disrupt ecosystems.

Once launched, the receptacles would travel to the place between the Earth and sun where their gravitational fields cancel out, allowing objects to remain stationary relative to the two bodies. This is where the contents would be released. Scientists think they could be kept in place for 50 years or more.

Even with the best will in the world, reducing our carbon emissions is not going to prevent global warming. It has become clear that even if we take the most drastic measures to curb emissions, the uncertainties in our climate models still leave open the possibility of extreme warming and rises in sea level. At the same time, resistance by governments and special interest groups makes it quite possible that the actions advocated by climate scientists might not be implemented soon enough. Is the game up in that case?

Quite recently a growing number of researchers have been taking a fresh look at large-scale 'geo-engineering' projects that might be used to counteract global warming. Basically the idea is to apply 'sunscreen' to the whole planet. It's controversial, but recent studies suggest there are ways to deflect just enough of the sunlight reaching the Earth's surface to counteract global warming. Climate models show that blocking just 1.8 per cent of the incident energy in the sun's rays would cancel out the warming effects produced by a doubling of carbon dioxide and other gases in the atmosphere. That could be crucial, because even the most stringent emissions-control measures being suggested would leave us with a doubling of carbon dioxide by the end of this century, and that would last for at least a century more.

There are two distinct proposals: reflecting away sunlight within the Earth's atmosphere, or blocking it in outer space. Each approach has its supporters and detractors. While tinkering with the atmosphere is likely to be much cheaper and simpler, space-based approaches may be longer-lasting and less likely to cause unwanted side effects – though they are much more technically challenging.

In addition, since it is naturally present at great heights above the earth, some researchers think an increase might not present as many unforeseen risks as some other suggested remedies for global warming, such as seeding the ocean with iron filings or other nutrients to encourage the growth of carbon-consuming organisms.

These drawbacks have driven others to look seriously at larger-scale, more expensive alternatives that might carry fewer risks. One that might do the trick is a space-based sunshade system. It may sound wildly implausible but some scientists are convinced that it is feasible.

These simple devices would be packed into metal containers in stacks of a million and propelled into space using electromagnetic rail guns – a method that has been tested in labs but never actually used. The acceleration is far too rapid for people or delicate equipment, but the method has long been proposed for shooting bulk material into space, such as water, rocket fuel or building materials. It could be cheaper and more reliable than traditional rockets.

Independent computer simulations show that the space sunshade could almost cancel out the temperature changes expected from global warming, except for a small area around each pole. That's because while greenhouse warming is uniform, the poles receive less sunlight than the tropics, so the effect of changes in sunlight is weakest at the poles. This regional difference in cooling might cause unpredictable changes in weather patterns. And since the poles would see less of an effect from the dimming, they might still experience a significant loss of ice cover.

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