In other words, we would build a gigantic parasol in outer space and try to position it between the Earth and the sun. At least some of the radiation that comes in from the sun would then be obstructed before it hits our planet and the average temperatures on the surface of the Earth would begin to fall.

Would it work? Well, theoretically yes, but it would be incredibly difficult to build and might not be ready until long after some terrible climate apocalypse has already destroyed the Earth.

In addition, it’s difficult to predict the long-term impact of a simple mirror in one specific location. On a day-to-day basis, the Earth’s climate is reasonably predictable, partly because the forces that act upon it are more or less the same each day.

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If we start to interfere with the incident radiation from the sun it is hard to know how such a change would affect weather patterns. Various studies have predicted that rainfall in certain parts of the world might suddenly fall, reducing crop yields.

Indeed, many scientific papers point out that we still don’t know enough about the knock-on effects of such technology, termed geoengineering, or potential ethical or legal issues in its use. The United Nations’ Intergovernmental Panel on Climate Change reports have been cautious about the technology for this very reason.

In 1989, American scientist James Early was working at the Lawrence Livermore National Laboratory, in California. Within the scientific community, the idea of climate change and global warming had already been recognised although it would be some years before mainstream political debate would take up these themes in earnest.

Early looked at the possibility of placing a gigantic mirror in outer space that would blot out the sun’s rays (or at least part of them) thus lowering the surface temperature of our planet. It is a simple, if ambitious, approach to a complicated problem.

His plan would involve building a mirror that was about 2,000km wide. The mirror would be assembled at the Lagrange point (L1), where it would hold its position between the Earth and the sun. People looking up at the sun would be unlikely to notice any difference in the intensity of sunlight; remember, we are only talking about a 1 per cent reduction in sunlight intensity.

However, the actual mass of the mirror would be immense, much too large for us to readily launch into outer space. The only way to build such a mirror, Early suggested, would be to mine raw materials on the moon and transfer them into lunar orbit, where they could be processed into metals.

If a 2,000km wide mirror sounds large, one way to make it sound slightly more realistic is to bear in mind that it need only be one-thousandth of a millimetre thick. A fantastically small veneer of elemental aluminium would be enough to reflect most of the incident sunlight and in the vacuum of space, the actual metal would never be blemished by oxidation.

Aluminium on Earth is a dull grey colour because its surface has reacted with the Earth’s atmosphere. The production process would have to be done by robots.

More recently, Lowell Wood, a senior staff scientist at the Lawrence Livermore lab suggested that putting wire mesh mirrors into orbit around the Earth might deflect enough sunlight to save us from the worse effects of global warming.

He calculated that reflecting 1 per cent of incident sunlight would restore climate stability, arguing that one mirror measuring 1.6 million sq km, or several smaller ones, could just about do it.

Roger Angel, a professor of astronomy at the University of Arizona, has proposed sending millions of small mirrors into orbit around the Earth in a bid to block 1 per cent of incident sunlight.

What impact would this really have? It is impossible to say. Systems such as these would be so complex that we can’t be sure how global climate, weather patterns and harvests would be affected.

Star Technology and Research suggested hundreds of space mirrors to block sunlight reaching the equator. What’s attractive about these last two ideas is that the challenge of launching each small mirror is much less significant than launching one large one.

As each mirror was released into low-Earth orbit, we would be able to make at least some sort of attempt to measure any reduction in global temperatures that followed, even if the early changes were only incremental.

The most intense sunlight reaching the Earth’s surface strikes it at the equator. Since the Earth is rotating at about 1,600km/h at this point, the surface soon cools down during the course of the 12-hour night (the day-night cycle always being 12 hours at the equator.) The full force of the sun’s rays hits the same surface again the following morning, building up to maximum intensity around midday.

Sunlight intensity at the equator is significantly compromised by the relatively high presence of cloud cover but, overall, the equator would be the most obvious place to obstruct sunlight in order to reduce the temperature of the Earth.

A series of several hundred aluminium parasols orbiting several hundred miles over the equator would downgrade the intensity of sunlight hitting the Earth, although it is difficult to predict the long-term consequences. The exhaust gases released by the launch rockets alone might be enough to undermine the benefits of any increased shade.

Rising global carbon dioxide (CO2) levels in the atmosphere may have implications that go far beyond those of rising temperatures. CO2 is a water-soluble gas that can easily be absorbed by the Earth’s oceans and some scientists predict that the seas will experience a significant fall in pH value with potentially catastrophic consequences for marine life.

At this point, we probably ought to mention that about a third of the photosynthetic elimination of CO2 from the Earth’s atmosphere is currently performed by ocean-going algae with another third being carried out by the world’s rainforests.

If we knock out one-third of CO2 consumption due to acidification of the oceans, it is hard to gauge what the impact might be on climate change, but it wouldn’t be good.

Even if a system of space mirrors proved to be effective, rising CO2 levels might yet destroy us by other means. Nobody knows. It is incredibly difficult to predict how complex systems will change in the face of any provocation.

The process of looking at as many potential solutions as possible to the climate crisis has led to the emergence of a new field of climate, or geo, engineering.

If the idea of blasting something into deep space to save us from disaster sounds far-fetched, it might be easier to get your head around the possibility of building a series of large balloons and releasing them into the upper atmosphere.

The balloons would be designed to be highly reflective of sunlight and if enough of them were built (we are talking thousands) then eventually the amount of sunlight reflected would be enough to lower the temperature of the surface of the Earth, while they could also possibly release sulphate droplets into the atmosphere to simulate the effects of an erupting volcano.

In 1991, the previously dormant volcano Mount Pinatubo, in the Philippines, erupted, unleashing millions of tonnes of sulphur dioxide into the atmosphere.

According to the Nasa Earth Observatory, writing in 2001, a decade after the event: “The Pinatubo eruption increased aerosol optical depth in the stratosphere by a factor of 10 to 100 times normal levels measured before the eruption. (‘Aerosol optical depth’ is a measure of how much light airborne particles prevent from passing through a column of atmosphere.)

“Consequently, over the next 15 months, scientists measured a drop in the average global temperature of about 0.6C.”

Some scientists have looked at this and concluded that the same technique might be used to deliberately adjust the Earth’s climate. It sounds like the climax to a science fiction movie.

Inspired by this kind of thinking, Daniel Schrag, a professor of environmental science at Harvard University, and David Leith, at the University of Calgary, organised a conference in 2007 and felt it was worth looking into such ideas.

As with all of the research in this area, there is much still to be assessed. Critics of this idea say that lowering the temperature of the Earth by absorbing the sun’s radiation could have unexpected effects on weather patterns and crop yields.

The release of sulphur aerosols could also have a depleting effect on the ozone layer, not to mention the “sky whitening” that might take place as blue skies hazed over.

It has been suggested, too, that a fine mist could be generated from seawater by specially designed machines spread around the world. Some of this work has focused on increasing the reflectivity of the clouds themselves.

In particular, stratocumulus clouds over the world’s oceans that reflect about 30 to 60 per cent of the sun’s radiation. Simultaneously, they lower the temperature of the sea below them.

Such clouds cover about one-fifth of the world’s oceans. Various ideas have been suggested for pumping a fine mist into these clouds to increase their reflectivity and lower surface temperatures this way. These are sometimes referred to as marine cloud brightening.

All of this is fascinating, and plenty see the case for further scientific study, but will one of these tech­nologies save us from climate disaster? Many scientists see such technology as a supplementary effort, rather than a silver bullet, but who knows what further research might reveal?

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