forecasts for global temperatures grow increasingly dire,

scientists are taking a serious look at an idea once considered crazy: reengineering the atmosphere
The sudden explosion of Mount Pinatubo on June 15, 1991, sent a vast column of ash into the sky, blotting out the sun, killing hundreds and demonstrating one way to save humanity from a potential climate disaster. The mountain’s 20 million tonnes of sulphur dioxide rose from the Philippines into the stratosphere, blanketing the planet in a haze that reflected part of the sun’s heat back out into space. Over the next several years, the haze lowered the earth’s temperature by a cumulative total of half a degree Celsius—setting the clock back on global warming. In the century before Pinatubo, greenhouse gases released by human industry had helped raise the earth’s temperature by 1 degree.

The effect was temporary, but scientists began to wonder if the volcano hadn’t revealed a possible weapon against climate change. A judicious application of sulphur dioxide to the upper atmosphere, which could be accomplished by launching the gas from rockets, spraying it from high-altitude planes or releasing it from a big chimney, would have an almost immediate impact on temperature. And it would cost a thousand times less than even the most optimistic scenarios for cutting emissions. A small group of scientists began looking into how this kind of geo-engineering could be done most efficiently and with the fewest side effects.

Over the past two decades geo-engineering began to include other ways of fixing climate, including new spins on the Pinatubo effect. Using sulphur dioxide or other materials, they aim to reflect sunlight back into outer space. One would boost a series of mirrors into orbit, shading Earth from sunlight, but at a cost that would likely bankrupt the planet. In the 1990s, the controversial inventor of the hydrogen bomb, Edward Teller, proposed floating reflective particles of metal in the atmosphere, adding a Dr Strangelove air to the geo-engineering field.

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