Bad news on the climate front

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Bad news on the climate front. It was already clear we are likely to go into runaway warming later this century, because greenhouse emissions are not dropping.

World View by Gwynne Dyer

We did have a fall-back position, which was to counter the warming by geo-engineering, but now the leading technique for geo-­engineering looks like it will not work.

In a paper published this month in Environmental Research Letters, three researchers at Reading University in England have shown that trying to cool the planet by putting large amounts of sulphur dioxide into the stratosphere would lead to a 30% decline in rainfall in most of the tropics.

That would mean permanent drought conditions in countries like Indonesia, and millions would starve.

The standard assumption was that even in runaway warming there would still be as much rain in the tropics as before, if not more. But Angus Ferraro, Ellie Highwood and Andrew Charlton-Perez have examined the effect of geo-engineering on the “tropical overturning circulation,” and it’s not good.

In the tropics, this circulation is largely responsible for lifting water vapour from the surface high up in the atmosphere, where it turns back into water droplets and falls as rain. If the circulation gets weaker, so does the rainfall.

Putting sulphur dioxide into the stratosphere to cut the amount of incoming sunlight and reduce heating at the surface was first suggested by Paul Crutzen, a Nobel Prize-winning atmospheric chemist, in 2006. Crutzen pointed out that large volcanoes, when they explode, put substantial amounts of sulphur dioxide gas into the stratosphere.

That causes significant cooling at the surface for one or two years, until it all comes down again and it does no apparent harm in the process. The last big volcano to explode, Mount Pinatubo in the Philippines in 1991, reduced the average global temperature by half a degree C.

Human beings also could put sulphur dioxide into the stratosphere (on a rather larger scale), to hold the temperature down, said Crutzen. The ice caps wouldn’t melt, our agriculture would continue to get the familiar weather it needs, and we would win ourselves more time to get our emissions down.

We still have to get our emissions down in the end, he stressed, but it would be better not to have a global calamity on the way from here to there.

But the Reading University scientists have discovered a hitherto unsuspected side-effect of this kind of geo-engineering.

The sulphur dioxide particles don’t just reflect back a portion of the incoming sunlight from above. They also reflect a portion of the long-wave radiation (heat)) coming back up from the ­surface, and that heats the top of the troposphere.

The troposphere is the lower part of the atmosphere, where all the weather happens.

If you heat the top of the troposphere, you reduce the temperature difference between there and the surface, so the tropical overturning circulation weakens.

That means less water vapour is carried up, and less rain falls back down. Result: drought and famine.The sulphur dioxide solution was the cheapest and seemingly the best understood option for holding the temperature down.

A great many people were glad that it was there, as a kind of safety net if we really don’t get our act together in time to halt the warming by less intrusive means.

Now, there’s no safety net.

Dyer is a London-based freelance journalist.

 

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