Reversing climate change via huge artificial volcanic eruptions could bring severe droughts to large regions of the tropics, according to new scientific research.

 

The controversial idea of geoengineering – deliberately changing the Earth's climate – is being seriously discussed as a last-ditch way of avoiding dangerous global warming if efforts to slash greenhouse gas emissions fail.

 

But the new work shows that a leading contender – pumping sulphate particles into the stratosphere to block sunlight – could have side-effects just as serious as the effects of warming itself. Furthermore, the impacts would be different around the world, raising the prospect of conflicts between nations that might benefit and those suffering more damage.

 

The study, published in the journal Environmental Research Letters, is the first to convincingly model what happens to rainfall if sulphates were deployed on a huge scale.

 

While the computer models showed that big temperature rises could be completely avoided, it also showed cuts in rain of up to one-third in South America, Asia and Africa. The consequent droughts would affect billions of people and also fragile tropical rainforests that act as a major store of carbon.

 

The study considered what would happen if carbon dioxide levels quadrupled in the atmosphere – the sort of extreme situation in which geoengineering might be seriously considered. Without intervention, temperatures rose by 4C, far above the 2C level considered dangerous by the world's governments.

 

But the temperature rise was reduced to zero if a massive geoengineering effort took place. The 60m tonnes of sulphur dioxide pumped into the stratosphere each year in the simulation is equivalent to five volcanic eruptions, each on the scale of Mount Pinatubo, the huge 1991 eruption in the Philippines that cut global temperatures by about 0.5C in the following year or two.