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This was one of the biggest volcanic explosions in history. It happened on June 15th 1991 in the north-west of the Philippines. It was so powerful it produced a gas cloud that reached the stratosphere. The explosion caused a lot of damage locally but the cloud itself did something extraordinary – it lowered the Earth’s temperature for four years.
Sulphur dioxide in the cloud created particles which spread around the Earth. These then reflected some of the sun’s rays into space. Scientists are looking to mimic the effects of this phenomenon to counter global warming. It’s a highly controversial concept known as solar geoengineering. Climate change is probably the biggest problem humanity faces today. In the past 25 years the global average temperature has risen by 0.5°C
So far governments have focused on policies for cutting emissions but they keep rising. The concentration of carbon dioxide in the atmosphere has risen 15% since 1994. The Paris agreement, signed by 175 parties in 2016 was a sign that countries were willing to work together to cut emissions. But not every world leader is on board.
If emissions aren’t reduced, what next?
In that Harvard and Yale study they imagined building a fleet of planes – up to 95 of them that would make 60,000 flights a year. The fleet would spread hundreds of thousands of tonnes of sulphur dioxide into the stratosphere every year. After 15 years they reckon the world would cool by 0.3°C. But there are reasons not to do this. One of the biggest concerns is that it could make governments complacent.
It would also be politically messy. If the plan is to put a thermostat on the Earth deciding who has their hand on the dial won’t be easy.
A Swiss proposal to study geoengineering and how it should be regulated was recently put forward at the UN Environment Assembly. But America and Saudi Arabia opposed the motion – possibly because they don’t want international regulation of geoengineering. As things stand not enough is known about how it could impact the climate or the chemistry of the atmosphere.
There could be unexpected consequences.
The politics of solar geoengineering are so complex that it might never happen. That said, as the world continues to warm the case for exploring radical measures grows stronger.