PARIS: Former political leaders and heads of international organisations called on Thursday for national moratoriums on deploying technologies to slow global warming by dimming the impact of the Sun.

The Climate Overshoot Commission said research and experiments into so-called solar radiation modification (SRM) should move forward, but only under international supervision and in jurisdictions with strong environmental safeguards.

Currently, there is no formal global governance for the development or deployment of such technologies, and an incomplete understanding of the risks they carry.

“We need a moratorium,” commission member Laurence Tubiana, head of the European Climate Foundation and an architect of the Paris Agreement, said.

Artificial cooling of Earth’s surface likely to disrupt monsoon rains in South Asia and western Africa

“We know the risks — this is not a silver bullet solution.” The failure to reduce the greenhouse gas emissions that drive global heating has led to suggestions that solar geoengineering — widely dismissed a decade ago as unnecessarily risky — could buy time while the world scales up emissions reductions and CO2 removal.

Barely 1.2 degrees Celsius of warming so far has boosted the intensity, frequency and duration of deadly and destructive heatwaves, droughts and mega-storms.

The 2015 Paris climate treaty calls for capping the rise in Earth’s surface temperature to 1.5C above mid-19th century levels to avoid catastrophic impacts.

The commission takes its name from the strong likelihood that warming will breach, or “overshoot”, that target, probably within a decade, according to the UN’s Intergover­nmental Panel on Climate Change (IPCC).

In 2018, the IPCC concluded that greenhouse gas emissions must drop 43 per cent by 2030 in order to cap global warming at the 1.5C threshold. Solar radiation modification methods include brightening marine clouds by seeding them with salt particles from the ocean, and placing giant mirrors in space to reflect away Earth-bound sunlight.

But the technique thought to have the highest potential is injecting aerosols — especially sulphur particles — into the stratosphere to reflect sunlight back into space.

Nature sometimes does the same: the violent 1991 eruption of Mount Pinatubo in the Philippines — which spewed millions of tonnes of dust and debris — lowered global temperatures for about a year, especially in the Northern Hemisphere.

But there is growing evidence that the advantages of cooling Earth’s surface must be weighed against unwanted side effects.

Artificially dimming the Sun’s radiative force is likely to disrupt monsoon rains in South Asia and western Africa and could ravage the rain-fed crops upon which hundreds of millions depend for nourishment, several studies have shown.

It could also reverse progress in the recovery of the ozone layer that shields life on Earth from deadly ultraviolent radiation, according to the Scientific Assessment of Ozone Depletion report earlier this year.

Scientists likewise warn that Earth’s surface would heat rapidly if seeding

the atmosphere with Sun-blocking particles were to suddenly stop, known as “termination shock”.

Published in Dawn, September 15th, 2023