As global temperatures climb and extreme weather events become more frequent, scientists are exploring the use of solar geoengineering, a set of different measures all geared towards reflecting sunlight and cooling the Earth.
“The world is making progress on emissions,” says solar geoengineering researcher Dr Pete Irvine of the University of Chicago, “but even if every country meets its current pledges, we are still tracking towards more than 2.5 degrees of warming by century’s end.”
That level of warming could lead to severe impacts such as loss of biodiversity, health crises and unchecked polar melting, adds Irvine, who the cofounder of SRM360, a nonprofit hub investigating ways to reflect the heat of the sun.
There are other strong voices in the scientific community that argue solar geoengineering measures could – if successful – simply relieve the urgent pressure to implement necessary deep cuts to greenhouse gas emissions.
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Irvine argues that emissions cuts need to happen come what may, and that solar geoengineering should not be seen as a substitute for emissions cuts or carbon removal schemes but as an added measure to help cool the planet.
Eliminating emissions will stop climate change from worsening, but to actually bring temperatures back down to a safer, more stable level will need removal of hundreds of billions of CO2 already in the atmosphere, says Irvine. “Solar geoengineering could help us manage risks along the way.”
Scientific techniques that seek to reflect the sun’s energy back into space, and thus cool Earth, are all referred to as solar geoengineering, or as sunlight reflection methods (SRM). There are two leading strategies aiming to do this.
There is stratospheric aerosol injection (SAI), which involves releasing fine, reflective particles, such as sulphur compounds, into the upper atmosphere. Scientists say it could reduce global temperatures by 1 degree if deployed widely.
The other option is marine cloud brightening (MCB). The goal here is to make low-lying clouds more reflective of sunlight. This is achieved by injecting tiny particles of sea salt into the clouds – making them brighter, and increasing their ability to reflect sunlight away from the Earth and back into space.
Irvine says that although SRMs are beneficial, none of them alone can fully address the root cause of the warming problem: the build-up of greenhouse gases in our atmosphere. “They can’t stop acidification of oceans or repair ecosystems already damaged by climate pressure.”
Their implementation can carry a risk of harmful side effects. Measures to introduce SAI, for instance, could result in increases, albeit mild, in acid rain, and potential delays in healing of the ozone layer.
And there is even a risk of a “termination shock”, Irvine adds, which is a risk of a rapid spike in temperature if SRMs were started and then abruptly halted.
The global politics involved could be tricky, too, he says, if countries become suspicious of each other’s actions or motives. “Imagine a powerful country deploying SRM unilaterally. Even if their intention was to benefit everyone, perception matters. What happens if droughts or storms are blamed, rightly or wrongly, on their actions? The risk of conflict, or global mistrust, is real.”
The big solar geoengineering efforts are happening outside Ireland, but there are interesting technologies and proposals being explored here.
Prof Frank McDermott, a geochemist at UCD, has spent many years investigating how rocks absorb CO2 from the atmosphere. In particular, his research focuses on carbonic acid – formed when CO2 dissolves in rainwater – and its interaction with common rocks in Ireland such as limestone and basalt.
Human activity has accelerated CO2 emissions, says McDermott, but the Earth’s ability to draw it down via rock weathering hasn’t kept up.
A proposed fix he is looking at involves grinding certain rocks into powder, spreading them on farmland or coastlines and enabling the rocks to absorb atmospheric carbon faster than they otherwise would. “It increases the reactive surface area – more contact, more drawdown,” he says.
This approach, which is called “enhanced weathering” has been trialled at sites in Co Wexford by McDermott working with Silicate, an Irish start-up team that has successfully used ground limestone and crushed concrete to capture CO2 and provide benefits to agriculture by adjusting soil pH levels.
The work has potential for use in Ireland but challenges remain, most notably the wide presence of nitric acid created during the manufacture of nitrogen fertilisers, which interferes with the natural absorption of CO2 by rocks.
Ireland’s temperate climate is also a factor, as this may limit weathering rate, and be a particular issue for naturally slower-reacting rocks such as basalt. Then, scaling up enhanced weathering would also require careful sourcing of limestone raw material and consideration of impacts on the land, adds McDermott.
“There’s promise, but questions of governance, land use efficiency and environmental impact remain,” he says. “We need more data, especially if Ireland wants to explore this method seriously as part of its climate action plan.”
There’s hesitancy in permitting CO2 injection here. We need a framework for long-term storage. Other countries are already doing this. Why not us?
Don MacElroy is a retired professor of chemical engineering from UCD, and founder of NEG8 Carbon. This spin-out company began life as Trinity Green Energies in 2014, arising out of carbon capture research at TCD and UCD.
The company has developed direct air capture (DAC) technology that removes CO2 from ambient air. It operates at low temperatures, consuming less energy than many existing models.
The NEG8’s DAC model can capture 6,000 tonnes of CO2 per year, says MacElroy. The aim is to reach 72,000 tonnes per annum – a figure roughly equivalent to the annual carbon emission output of 15,500 cars.
“Carbon capture doesn’t attract the same attention or funding as sectors like pharma or IT, even though it’s just as vital, if not more,” he says.
A question arising is: where to put the carbon once it has been captured?
Ireland has an opportunity offshore, he says, to harness several disused gas and oilfields, including Kinsale, and repurpose them for the storage of CO2 underground. The porous basalt under Co Antrim, and the natural aquifers off the coast offer other potential storing grounds.
One obstacle standing in the way of DAC is lack of regulation, says MacElroy. “There’s hesitancy in permitting CO2 injection here. We need a framework for long-term storage. Other countries are already doing this. Why not us?”
“With the right policies and international collaboration Ireland could become a leader in DAC, but we must act quickly – climate deadlines aren’t negotiable.”
It will take a global effort to achieve climate safety, yet the funding and the treaties that are required to underpin it have been slow to materialise.
Without this, says Irvine, there is a risk that “cowboy” climate initiatives, operating without oversight or international consent, may go ahead.
We are all in a place where “every tenth of a degree matters”, he says. “If something can shave off just half a degree, that means millions fewer impacted by heatwaves, crop failures or flooding.”
In Ireland we are playing catch-up, as the latest projections are that a 23 per cent reduction in greenhouse gas emissions will be achieved by 2030, far short of the legally mandated 51 per cent target.
Our emissions need to fall, and quickly, but it’s likely that this will not be enough to guarantee our future climate safety. To achieve that, Ireland needs local solar geoengineering efforts – such as pulling carbon out of the air and managing land to draw down CO2 – to work, along with bigger, global efforts to reflect heat from the sun back out into space.
Ireland needs to answer key questions to have a chance of success. Can enhanced weathering exist here alongside sustainable agriculture? Can DAC carbon storage go along with support for offshore renewable energies. Will the public accept the complicated ethics behind solar geoengineering or reject it?
