The mission to dim the SUN: How controversial geoengineering technique could cool the planet using existing aircraft READ MORE: Bill Gates-backed plan to block the sun and reverse global warming By WILIAM HUNTER Published: 14:00 BST, 28 April 2025 | Updated: 15:13 BST, 28 April 2025 It might sound like a Bond villain's sinister plot, but dimming the sun could be the key to fighting climate change. Scientists believe a controversial geo-engineering technique called stratospheric aerosol injection could be used to cool Earth. Like suncream for the planet, this technique would load the atmosphere with tiny reflective particles to reduce the amount of sunlight reaching Earth. Researchers from the University College London (UCL) claim this can be done with existing commercial aircraft. Scientists had previously thought that aerosol injection could only cool the climate if the particles were injected at altitudes over 12 miles (20km). But new computer models show that adding particles at just eight miles (13km) over the poles would noticeably cool the planet. This altitude is already reached by some commercial aircraft such as the Boeing 777F, opening the possibility of geo-engineering starting far sooner than expected. Lead researcher Alistair Duffey, a PhD student at UCL, told MailOnline: 'It is too early to say whether stratospheric aerosol injection is in fact a good idea, we simply don’t know enough yet for policy-makers to make a well-informed decision, which is why research in this area is so important.' Scientists say that a controversial geo-engineering technique called stratospheric aerosol injection could be used to cool the planet by dimming the sun A study shows that this could be done using existing aircraft such as the Boeing 777F flying at altitudes of eight miles (13km), rather than the altitudes over 12 miles (20km) previously thought necessary When the planet is warmed by the sun, heat gradually escapes back into space so that the Earth is kept at a fairly consistent temperature. But when 'greenhouse' gases like carbon dioxide are released by burning fossil fuels, they act like a blanket around the planet and prevent that heat from escaping. Decades of extensive research has shown conclusively that the planet is becoming warmer due to the build-up of these greenhouse gases. The idea behind geoengineering techniques like stratospheric aerosol injection is to counteract that warming, by reducing the amount of heat reaching Earth in the first place. In this study, the researchers used a computer simulation of the climate to look at what would happen if sulphur dioxide was injected into the atmosphere. Sulphur dioxide is a corrosive gas often produced by burning fossil fuels which can be harmful to humans in high doses and makes rain more acidic. However, when it mixes with other molecules in the air it forms an aerosol, a suspension of fine droplets, which are highly reflective. These shiny droplets reflect the radiation from the sun back out into space before it has a chance to warm the planet, balancing out some of the warming produced by greenhouse gases. There are a number of geo-engineering theories being proposed, including 'shinier crops and buildings to reflect more sunlight', microbubbles in the ocean and removing cirrus clouds Scientists simulated what would happen if planes injected 12million tons of sulphur dioxide a year at altitudes of eight miles (13km) during spring and summer could cool the climate by 0.6°C (1.08°F) (AI-generated image) The researchers' simulations found that injecting 12 million tonnes of sulphur dioxide a year at altitudes of eight miles (13km) during spring and summer could cool the climate by 0.6°C (1.08°F). That is roughly the same amount of sulphur dioxide released by the eruption of the Mount Pinatubo volcano in 1991, which also produced an observable dip in global temperatures. These lower-altitude injections weren't as effective as injections above 13 miles since the aerosol particles last just months rather than several years before falling to Earth. Likewise, the simulation showed that low-altitude injections only produced a noticeable cooling effect if they took place at latitudes of 60 degrees north and south of the equator. For reference, that is roughly the latitude of Oslo, Norway or Anchorage, Alaska in the north and below the southernmost tip of South America to the south. But the study offers the first evidence that geoengineering could be done with technology available to use today. Co-author Wake Smith, of Yale University, says: 'Although pre-existing aircraft would still require a substantial modification programme to be able to function as deployment tankers, this route would be much quicker than designing a novel high-flying aircraft.' However, the researchers warn that stratospheric injection is not a 'silver bullet solution' for climate change – and this technique is not without potential risks. This quantity of sulphur dioxide is equivalent to the amount released by the eruption of Mount Pinatubo (pictured) in 1991 The researchers found that increasing the altitude reduced the amount of sulphur dioxide needed (bottom-left graph) and increased the amount of cooling achievable using the same quantity of gas (top-right graph) Modified aircraft are already used to release aerosols into the atmosphere for cloud seeding to increase rainfall (pictured). Large, similarly modified planes could soon be used for cooling the planet Mr Duffey says: 'There are many risks, spanning the range from direct physical side-effects, such as acid rain, to indirect concerns around governance, conflict and geopolitical tension.' Additionally, although low-altitude injections are more achievable, they could cause more problems since they require more sulphur to achieve the same global cooling. NOAA floats idea to fight climate change that involves injecting the atmosphere with millions of tons of ice to cool the planet Yet one of the biggest criticisms of geoengineering is that it is a distraction from making the real, difficult changes that need to be made to limit climate change. 'One major risk is that even seriously discussing these ideas might distract from the vital effort to get to net zero emissions,' Mr Duffey adds. 'There is evidence it might help reduce impacts from climate change, but only if used in combination with rapid and deep cuts to emissions.’ Study co-author Dr Matthew Henry, of the University of Exeter, says: 'Stratospheric aerosol injection is certainly not a replacement for greenhouse gas emission reductions as any potential negative side effects increase with the amount of cooling: we can only achieve long-term climate stability with net zero.' WHAT ARE THE SIDE EFFECTS OF GEOENGINEERING STRATEGIES? Scientists have proposed all sorts of solutions to fight climate change, including a number of controversial geoengineering strategies. Among the many include: Afforestation: This technique would irrigate deserts, such as those in Australia and North Africa, to plant millions of trees that could absorb carbon dioxide. Drawback: This vegetation would also draw in sunlight that the deserts currently reflect back into space, and so contribute to global warming. Scientists have proposed all sorts of solutions to fight climate change. File photo Artificial ocean upwelling: Engineers would use long pipes to pump cold, nutrient-rich water upward to cool ocean-surface waters. Drawback: If this process ever stopped it could cause oceans to rebalance their heat levels and rapidly change the climate. Ocean alkalinisation: This involves heaping lime into the ocean to chemically increase the absorption of carbon dioxide. Drawback: Study suggests it will have of little use in reducing global temperatures. Ocean iron fertilisation: The method involves dumping iron into the oceans to improve the growth of photosynthetic organisms that can absorb carbon dioxide. Drawback: Study suggests it will have of little use in reducing global temperatures. Solar radiation management: This would reduce the amount of sunlight Earth receives, by shooting reflective sulphate-based aerosols into the atmosphere. Drawback: Carbon dioxide would still build up in the atmosphere. Share or comment on this article: The mission to dim the SUN: How controversial geoengineering technique could cool the planet using existing aircraft Add comment