It began with a bang. In 1991, Mount Pinatubo in the Philippines blew its top. The largest volcanic eruption ever recorded spewed 17 million tonnes of sulphur dioxide (SO2) into the atmosphere. It devastated the local area. But cooled the Earth.

The gas formed a fine mist in the ozone layerA layer of gas around 10 kilometres above the Earth's surface which absorbs ultraviolet radiation (a type of heat that reaches the planet from the sun). The layer has a very important role as exposure to too much ultraviolet can be bad for living things., reflecting the sun's rays into space. The following year, global temperatures fell by half a degree Celsius. Now, scientists want to copy this cooling effect to tackle climate changeLong-term shifts in temperatures and weather patterns. Human action is a major cause of climate change..

The technology is called solar radiation management (SRM), and philanthropistsPeople who donate generously to good causes. like Bill GatesFounder and former CEO of Microsoft, the company responsible for popularising household computers in the 80s (and still one of the major global tech companies). His house on the shores of Lake Washington is called Xanadu 2.0. It took seven years to build and is seen as an early example of a smart home. are funding its research. A fleet of planes injecting reflective aerosol particles into the stratosphereA layer of the atmosphere which extends for 31 miles above the Earth's surface. could create a "global thermostat" to control global temperatures.

In California, the tech startup Make Sunsets has already released dozens of small balloons. Company founder Luke Iseman aims "to cool the Earth as quickly as we safely can". But Iseman's experiments have alarmed scientists who want more regulationWhen governments step in to control what (and how) people buy and sell things..

Until recently, few took the idea seriously. But this year, the UNUnited Nations. An intergovernmental organisation based in New York that aims to maintain international peace and security. warned we are failing to cut CO2 emissions fast enough to stop a 1.5C rise in global average temperatures above pre-industrial levels.¹ A UN report said SRM is the "only" way to cool the planet in the short term.

In February, two open letters supporting SRM research garnered hundreds of signatures from climate scientists. GeoengineeringDeliberate attempts to intervene in the Earth's natural processes to counteract climate change on a large scale. expert Daniele Visioni says the technology is "risky," but we should not reject "an additional tool to fight global warming".

The issue divides climate experts. Physicist Raymond Pierrehumbert calls it a "big distraction" from cutting CO2 emissions. Activists fear a "technological fix" provides an excuse for polluters to ignore net zeroWhen the gases going into the atmosphere are balanced by those being taken out of it. targets.

Others warn SRM could have unintended consequences and cause unpredictable extreme weather. One model shows it may increase drought risk in sub-Saharan Africa. But Pierrehumbert says the worst drawback is what happens if the project stops.

"You're setting the world up for a real catastrophe," he warns. Once the reflective aerosols dissipate, temperatures will skyrocket. To avoid this "terminal shock," we would need global cooperation to keep thousands of planes in the air for hundreds of years.

Who will control the global thermostat? The US and Saudi Arabia have blocked moves to regulate SRM. This worries climate scientist Claudia Wieners, who says we must "stop crazy people doing crazy stuff". Acting alone, one country or company could drastically change the Earth's atmosphere.

Wake Smith at Yale University says geoengineering is "inevitable" but will not fix climate change. He likens it to a "fire extinguisher" for emergency use only. And Luke Iseman of Make Sunsets says: "this is an emergency".

July was the hottest month in human history. A Greek wildfire is the largest ever seen in Europe. "The era of global boiling has arrived," says UN chief Antonio Guterres. And the temptation of a quick fix is greater than ever.

Yes: Deliberately polluting the atmosphere with sulphur dioxide is a foolish act of desperation. We won't know the effects until it is too late. And meanwhile, we will grow complacent about CO2 emissions.

No: Human activity is already putting aerosols into the air. It is responsible for offsetting a third of greenhouse gas climate warming.² All SRM means is taking control of our atmosphere and our survival.

Or... All technology comes with risks. And doing nothing is also dangerous. That is why climate scientists demand further research, regulation and debate to find the best solutions to climate change.