Ross Clark Ross Clark

Should we be looking at geo-engineering the climate?

Credit: Getty Images

Has a well-meaning international effort to cut pollution from ships contributed to a sudden warming of the waters in the north Atlantic this year? That is the extraordinary claim made this week in an article in Science magazine, the journal of the American Association for the Advancement of Science. It asserts that limits on the sulphur content of fuels used by ships have helped reduce sulphur pollution from those vessels by 80 per cent – but at the inadvertent cost of reducing cloud formation over the oceans and so speeding global warming.  

Previously, well-used corridors of the Atlantic Ocean were covered with ‘ships tracks’ – yellowish, elongated clouds which followed the paths of passing ships. Now, the clouds have been diminished, and the waters are exposed to the full power of the sun, resulting in record sea surface temperatures. As Michael Diamond of Florida State University puts it, ‘It’s as if the world suddenly lost the cooling effect from a fairly large volcanic eruption each year.’ Sulphur Dioxide emissions from the eruption of Mount Pinatubo in the Philippines in June 1991, for example, have been claimed to have reduced global temperatures by 0.3 Celsius for three years. 

The world is better off without the air above the oceans polluted with sulphur. It was sulphur emissions from coal-burning power stations which was responsible for acid rain. Yet the theory that ocean-warming has been exacerbated by a fall in clouds generated by ships’ exhausts has rekindled the question: should we be employing ‘geo-engineering’ in order to try to combat climate change?  

The idea has been around a long time. Experiments in cloud-seeding by spraying silver iodide or other chemicals into the atmosphere have been carried out since the 1940s – with conflicting claims as to their success.

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