Geoengineering has been the subject of conspiracy theories, but could it help save the planet?
- author, Simon King
- role, Lead Weather Presenter
If drastic cuts in carbon dioxide emissions won’t control the rise in global temperatures, could something called geoengineering be a way to cool the planet?
Scientists around the world, including in Britain, are researching geoengineering – ways to manipulate the climate to combat global warming – which is already a £103 billion ($135 billion) industry.
Some experts worry there are too many risks associated with the phenomenon, arguing it could disrupt global weather patterns and cause some regions to warm rather than cool.
As the industry grows, so do conspiracy theories. BBC Weather has seen a significant increase in comments about geoengineering on social media since January, with people accusing BBC Weather of covering up secret projects or falsely blaming geoengineering for the recent cold and wet weather. Globally, geoengineering has been mentioned twice as many times this year on X (formerly Twitter) as it was in the past six months of 2023.
One idea for geoengineering is to cool the planet by reflecting sunlight back into space. The most advanced branch of geoengineering is direct air carbon capture, with small-scale facilities operating in Europe, the US and Canada. Currently, these facilities remove about 10,000 tonnes of carbon dioxide per year (one-third of London’s annual emissions), but this means that massive scale-up is needed to make any difference to the roughly 35 billion tonnes emitted globally.
“We need to start thinking about what else we can do to limit further warming,” said Professor Liz Bentley, chief executive of the Royal Meteorological Society. “And that’s where geoengineering starts to become an interesting discussion.”
Aside from concerns that geoengineering could worsen the effects of climate change, some experts worry that the temptation to view it as a temporary solution could distract us from efforts to reduce carbon emissions.
It’s not as strange as it seems
While it sounds like something from science fiction, the idea of reflecting solar radiation, the technical term for sunlight, isn’t all that far-fetched, and it does occur in nature from time to time: Volcanic eruptions can send large amounts of ash and aerosols into the upper atmosphere, reflecting solar radiation back into space.
Image source, Getty Images
In 1991, Mount Pinatubo in the Philippines erupted, causing a drop in global average temperatures by 0.5°C in the following years.
So, can we really recreate volcanoes to cool the planet?
Prof Jim Heywood, an atmospheric scientist at the University of Exeter, urges caution: “We want to know not only the harmful effects of climate change, but also the potential side effects or harmful effects of deploying solar radiation management,” he said.
The researchers are studying two types of solar radiation management: marine cloud brightening and stratospheric aerosol injection.
To increase the brightness of marine clouds, very fine seawater is sprayed from a ship into low-lying clouds over the ocean, increasing the cloud’s brightness and reflectivity.
Modelling shows that brightening clouds by spraying it over a wide area near the equator (about 4% of the ocean) could lead to increased cloudiness and therefore lower sea surface temperatures underneath, with potential global implications.
Our atmosphere is complex, has no boundaries and behaves like a fluid. You may have heard of the “butterfly effect” – a butterfly flapping its wings in Mexico can bring rain to the UK. In reality, that’s a big leap, but it highlights how connected the weather is around the world.
“Lightening clouds off the coast of Namibia could potentially trigger droughts in South America, particularly Brazil, and what’s there? Well, rainforest,” Prof Heywood said.
In this case, complex atmospheric and oceanic circulation means that brighter clouds would cool the ocean surface in the eastern South Atlantic, adversely affecting rainfall patterns from the South Atlantic to South America. Drought in the Amazon rainforest, often called the “lungs of the Earth” because it absorbs carbon dioxide, could be quite damaging.
While much of the focus has been on harnessing marine cloud brightening to offset rising global temperatures, some see opportunities to use it on a smaller scale.
Following the widespread coral bleaching event on the Great Barrier Reef in 2016, scientists at Australia’s Southern Cross University are experimenting with brightening clouds that protect and cool coral-rich areas of the reef to prevent bleaching during marine heatwaves.
Image source, Southern Cross University
“Although we are still in the early stages of understanding how marine cloud brightening applies over the Great Barrier Reef, we have made great scientific progress.
“We now have much more confidence that we can brighten clouds over coral reefs,” said project leader Professor Daniel Harrison, from Southern Cross University.
Stratospheric Technology Development
The technology already exists to brighten marine clouds on a small scale using fans and sprayers, but stratospheric aerosol injection, another method of managing solar radiation, needs further advances to have the desired effect.
This method of geoengineering involves artificially adding aerosols, such as sulfates, to the stratosphere, which extends from 6-12 miles (10-20 km) to 31 miles (50 km) above Earth. These aerosols reflect some of the solar radiation, reducing the amount that reaches the Earth’s surface, theoretically causing a cooling of the planet.
Image source, Getty Images
It’s not clear how much aerosol could be injected into the stratosphere, but one idea is to use an aircraft capable of flying at an altitude of 11 miles (18 kilometers), about 1.5 times that of a commercial airliner.
It would take millions of tons of sulfur dioxide to have any effect: for example, about 15 million tons of sulfur dioxide injected into the stratosphere during the eruption of Mount Pinatubo reduced global temperatures by 0.5 degrees.
Stratospheric aerosol injection is only considered a short-term option because sulfate aerosols only remain in the atmosphere for a few years, whereas carbon dioxide remains in the atmosphere for decades.
Despite this, one US company has started selling “refrigeration credits” – for a fee, the company will send balloons filled with sulphur dioxide into the stratosphere, where they will burst and release the gas.
Image source, Getty Images
They suggest that one cooling credit, two grams of sulfur dioxide, “offsets one tonne of carbon dioxide warming in one year.” This is the equivalent of one passenger flying from Paris to New York and back, so a lot of balloons would need to be launched to get any cooling effect.
As with marine cloud brightening, stratospheric aerosol injections also pose risks: A study earlier this year used computer modelling to find that they could cause strong warming 15 kilometres above the tropics, alter large-scale weather patterns, warm the poles and change rainfall patterns over land.
“The regional effects are poorly understood,” Prof Bentley said. “They could moderate global average temperatures. [rise]But it could make things worse in certain parts of the world.”
Danger warning
This leads to fundamental questions about the reliability and risks associated with this type of intervention. In 2022, hundreds of scientists signed an open letter calling for a global non-use agreement on solar radiation management.
They said the increased calls for development were a “cause for concern” as the risks involved were “not fully understood” and would hinder governments, businesses and society from moving towards decarbonisation.
The group worries that theoretical work could be carried out before real-world experiments can fully understand its shortcomings, but other scientists believe the risks of further exploring solar radiation management are smaller than those of relying solely on decarbonization.
Still others argue that misinformation and conspiracy theorists are hindering research.
“Many funders are highly sceptical about funding research for fear of being targeted by conspiracy theorists,” says Dr Ramit Debnath, an associate professor at the University of Cambridge, who analysed almost two million tweets with the hashtag #GeoEngineering and found that more than 70% expressed negative sentiment about solar radiation management, with the majority of these referring to conspiracy theories.
Image source, Getty Images
One of them concerns “chemtrails,” a widely-dismissed conspiracy theory about a secret plot to spray people with dangerous chemicals, but suggests that the white streaks in the sky coming out from the backs of planes are evidence of this. These are actually trails of condensed water vapour, known as contrails, that come from the planes’ jet engines.
Contrails at this altitude would actually absorb solar radiation and warm the Earth, so they have nothing to do with the geoengineering techniques currently being researched.
Dr Debnath says even talking about solar radiation management on social media means being accused of “trying to kill people and control their lives”.
Solar radiation management is being treated with caution: the UK government has not deployed the technology and has “no plans to do so”, but it is investing in it.
The Natural Environment Research Council is calling for applications for £10.5 million in funding to carry out a “risk-risk analysis” to assess whether the negative impacts of the technology are greater than the damage caused by climate change.
“This is not a silver bullet,” Prof Bentley said, “but it could be part of a suite of solutions.”
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