Duncan McLaren looks at proposals to develop a questionable engineering measure as a means to counter climate change.
The US-Israeli war on Iran has thrown energy resilience back into the spotlight. In many countries, the shock has strengthened the case for reducing dependence on fossil fuels and accelerating investment in reliable renewable energy systems. If sustained beyond the immediate crisis, that shift would cut emissions and improve resilience.
Yet the opposite dynamic is also visible. The US’ renewed embrace of fossil fuels, and its rejection of serious climate policy, has deepened fears that limiting global heating to well below 2°C — let alone the Paris Agreement’s 1.5°C aspiration — is slipping out of reach. One result is a worrying opening for solar geoengineering – a proposed collection of measures that together reduce the amount of sunlight reaching the earth’s surface that was once treated as a speculative distraction (see box: Is solar geoengineering pie in the sky?).
MCB is intended to increase the albedo (reflectiveness) of existing clouds. Condensation nuclei might be produced by dispersing salt and water vapour from the ocean surface using automated wind powered ships, or more speculatively, by drones. Thousands of ships would be needed to achieve a degree of global cooling.
The overall impact would depend on complex and poorly understood climatic connections between parts of the atmosphere. Practical experiments in Australia and the US have begun to explore ways to efficiently create a mist of condensation nuclei.
SAI seeks to emulate the cooling effects of large volcanic eruptions, with the introduction of sulphates or other natural or designed particles into the stratosphere by means such as aircraft, artillery or balloons. One US startup has already begun releasing balloons designed to burst in the stratosphere and release sulphur dioxide – but so far at an entirely negligible scale. Most serious researchers think distribution by novel aircraft designed to carry heavy loads to high altitudes (over 20 km high) is the most feasible.
Hundreds of aircraft constantly flying thousands of missions a year would be needed to implement one degree of cooling.
Both techniques could – in theory – halt warming, or even achieve some cooling within a few years – much faster than the effects of emissions cuts. And their direct costs are estimated to be relatively low compared to those of comprehensive decarbonisation. However, both the modelling and the volcanic analogues suggest that the cooling effects of either method of solar geoengineering would be uneven compared to greenhouse-gas caused warming, and would also likely result in unevenly distributed effects on precipitation. This is because reflecting incoming short-wave solar radiation has different effects than increasing outgoing long-wave radiation (the result of reducing greenhouse gas concentrations).
In other ways too, the impacts of solar geoengineering would not reverse those of greenhouse warming: ocean acidification would continue, for example. Moreover, should solar geoengineering be deployed to mask rising temperatures, and then halted abruptly, for any reason, temperatures would rebound rapidly – a phenomenon called termination shock. For all these reasons it is widely argued that solar geoengineering should not be seen as a substitute for other climate action, but, at best, as a supplement to slow the rise of temperatures or to ‘buy time’ for effective mitigation and adaptation.
Despite calls from scholars, and international bodies for a moratorium on deployment, exploration of solar geoengineering options is accelerating. Israeli-US startup company, Stardust has raised major funding to develop stratospheric aerosol injection technology. US think-tanks are framing control of such technologies as a matter of national security and “weather sovereignty”.
That solar geoengineering could become an excuse for delaying decarbonisation is a well-founded and long-standing fear.
In the UK, the Advanced Research & Invention Agency (ARIA) is funding outdoor experiments, while the Natural Environmental Research Council has supported modelling and public engagement. That engagement suggests UK publics are not necessarily hostile, but that any support for solar geoengineering – even for research – depends on credible governance and on emissions reduction remaining the priority.
That condition is crucial. That solar geoengineering could become an excuse for delaying decarbonisation is a well-founded and long-standing fear. But even if we could govern it well enough to avoid that risk, a deeper question remains: could geoengineering actually build climate resilience?
There are reasons why some think it might. Slowing the rate of warming could give societies more time to adapt. Cities cannot be redesigned for passive cooling overnight. Shade trees take years to grow. If stratospheric aerosol injection could shave the peak off temperature rise, it might reduce deadly heatwaves in the tropics and help protect outdoor workers. Marine cloud brightening has been proposed to reduce coral bleaching or slow ice-sheet melt. Some suggest solar geoengineering could reduce the risk of tipping events such as ice-sheet collapse or disruption of the Atlantic Meridional Overturning Current.
Some advocates therefore describe solar geoengineering as “radical adaptation”. The phrase blurs the boundary between climate action and technological climate control. It also avoids the harder question: what do we mean by resilience, and whose resilience are we protecting? (See box: Resilience and vulnerability)
Vulnerability is not simply an inherent property of people or places. It is shaped by political choices, economic structures, social exclusion, ecological damage and histories of exploitation. Resilience-building that ignores those drivers risks blaming the victims of climate change for their own exposure, rather than challenging the systems that made them vulnerable.
Resilience is not simply the ability to endure whatever the climate throws at us. It is the capacity of communities and systems to anticipate, absorb, adapt to and recover from shocks while protecting wellbeing, livelihoods and ecosystems. It is not something that can be delivered from the stratosphere. It depends on social, economic, ecological and political conditions on the ground.
That matters because vulnerability to climate change is not just an accident of geography or poverty. As adaptation scholars argue, vulnerability is produced by social norms, ecological conditions, economic bias and political choices. Many of those most exposed to climate harms have contributed least to the emissions that cause them. Their vulnerability is the consequence of colonial extraction, displacement from land, exclusion from commons and exploitative labour relations. In other words it is ‘imposed precarity’. Modern capitalism was founded on the creation of a precarious labour force, and the deliberate construction and maintenance of precarity in the interests of commerce and finance continues today, spreading and exacerbating climate vulnerability.
Unless climate responses tackle the drivers of vulnerability, they can make people less resilient over time.Solar geoengineering too must be judged against that test.
Climate resilience therefore cannot be separated from climate justice. A coastal community with insecure housing, low income, weak political voice and little access to public investment is not vulnerable merely because the sea is rising. It is vulnerable because economic and political systems have left it exposed. Similarly, gig workers facing extreme heat are vulnerable because labour markets have made their income insecure and their choices narrow.
This is why adaptation can become maladaptation. Sea walls can encourage more building in risky places. Insurance can make it easier to continue living or investing in areas exposed to wildfire or flood. Infrastructure can lock communities into brittle systems that fail under stress. Unless climate responses tackle the drivers of vulnerability, they can make people less resilient over time.
Solar geoengineering too must be judged against that test. In limited and well-governed circumstances, it might reduce some physical risks. If localised marine cloud brightening could protect a coral reef during an extreme heat event, or temporary cooling could reduce lethal heat stress, it would be irresponsible to dismiss research outright. Transparent public-interest research, shaped by public engagement and strict governance, is preferable to secretive commercial development backed by military-linked venture capital.
But even the best-governed solar geoengineering would not reverse climate change or restore damaged ecosystems. It would redistribute climatic effects unevenly. Nor would it repair unjust land relations or precarious labour markets. If controlled by a powerful state, and designed to protect national interests, it would likely export risk elsewhere.
That is the central danger. Solar geoengineering looks global, but governance is political. Decisions would be shaped by unequal power, security interests, commercial secrecy and geopolitical rivalry. Many vulnerable countries are sceptical of the prospects of geoengineering for good reason. They have already seen promises on mitigation, adaptation finance and loss and damage fall short. Why assume planetary cooling would be more democratic, just or reliable?
The risk of termination shock makes this worse. If solar geoengineering masked rising greenhouse gas concentrations and then stopped abruptly, temperatures could rebound rapidly. Communities would face a sudden climate jolt after years in which the pressure for real transformation had been weakened. A technology adopted as an insurance policy could become a trap.
If resilience means buying time and strengthening the existing economic order, solar geoengineering will appeal to those invested in climate procrastination.
The same applies to tipping points. Research on whether solar geoengineering could reduce the risk of ice-sheet collapse, Amazon dieback or AMOC disruption may be justified. But the most pressing conclusion from tipping-point science is not that governments should prepare to manage the sky. It is that accelerated emissions cuts and socio-economic transformation are urgent.
That is the nub of the issue. If resilience means buying time and strengthening the existing economic order, solar geoengineering will appeal to those invested in climate procrastination. But if resilience means reducing imposed vulnerability, rebuilding social and ecological capacity, and transforming the systems that create precarity, geoengineering is at best a marginal supplement and at worst a profound distraction.
The danger is political. In today’s world, solar geoengineering could make the current order more resilient to change. It could be abused to protect fossil assets, defer hard choices, and offer elites a way to preserve systems that generate vulnerability. That would not be climate resilience. It would be domination with a planetary thermostat, and a sword of Damocles, in the form of termination shock, hanging over us all.
This was edited for length with ChatGPT.
