Geoengineering Adaptation for Worst-Case Climate Change

Geoengineering, the deliberate large-scale manipulation of Earth’s climate systems, has emerged from academic debate to become a potential last resort in the fight against runaway climate change. These interventions carry enormous risks and plans should include them as last choices after all other strategies.

The Intergovernmental Panel on Climate Change (IPCC) has warned that limiting global warming to 1.5°C above pre-industrial levels is essential to avoid the most catastrophic impacts of climate change[i]. Yet, current trajectories suggest far more severe warming is coming. A study published in Nature Climate Change shows that there is a significant risk of exceeding 4°C of warming by 2100 under current policies[ii].

The consequences of such warming are almost unimaginable. There would be widespread ecosystem collapse, mass extinctions, severe food and water shortages, and the displacement of hundreds of millions of people. In this context, geoengineering looks less like a reckless gamble and more like a necessary risk.

Stratospheric Aerosol Injection

Among the various geoengineering proposals, Stratospheric Aerosol Injection (SAI) stands out as both the most discussed and potentially the most feasible. SAI involves injecting reflective particles, typically sulfur dioxide, into the stratosphere to mimic the cooling effect of volcanic eruptions[iii].

The concept is based on observations following major volcanic eruptions. For instance, the 1991 eruption of Mount Pinatubo in the Philippines injected about 20 million tons of sulfur dioxide into the stratosphere, resulting in a global cooling of about 0.5°C for the following year[iv]. SAI aims to replicate this effect on a controlled, ongoing basis.

The potential benefits of SAI are significant. It could provide a rapid cooling effect, potentially buying us precious time to reduce emissions and implement other mitigation strategies. Compared to the astronomical costs of unchecked warming, SAI is inexpensive. Some estimates suggest it could cost as little as a few billion dollars per year to deploy[v].

However, the risks associated with SAI are equally significant. One of the primary concerns is the potential disruption of global precipitation patterns. While SAI might successfully reduce global temperatures, it could lead to severe droughts in some regions and flooding in others. A study published in Nature Climate Change suggests that SAI could lead to significant changes in tropical precipitation patterns, potentially affecting the livelihoods of billions of people[vi].

There is also risk of damage to the ozone layer. The same sulfur dioxide particles that reflect sunlight can also catalyze ozone depletion, potentially exacerbating the very environmental problems we’re trying to solve[vii].

Most alarmingly, if SAI were to be suddenly discontinued—because of war, economic collapse, or other unforeseen circumstances—there could be abrupt and catastrophic warming as the masking effect of the aerosols disappears. This “termination shock” could lead to rapid temperature increases of several degrees within a decade[viii].

Despite these risks, recent models suggest that carefully managed SAI could reduce some climate risks without exacerbating others. A study published in Nature Climate Change found that a moderate deployment of SAI might halve the rate of sea level rise this century[ix]. However, the long-term effects remain uncertain, and the governance issues surrounding such a global intervention are daunting.

Ocean Fertilization

Another geoengineering technique that has garnered attention is ocean fertilization. This approach aims to increase carbon sequestration by stimulating phytoplankton growth through the addition of nutrients, typically iron, to iron-limited ocean regions[x].

The theory behind ocean fertilization is straightforward. Phytoplankton, like all plants, absorbs carbon dioxide during photosynthesis. By encouraging phytoplankton blooms, we might remove significant amounts of CO2 from the atmosphere. Some estimates suggest that large-scale ocean fertilization could sequester billions of tons of carbon dioxide annually[xi].

Increased phytoplankton growth might boost marine food chains, providing a secondary benefit to ocean ecosystems and fisheries. However, the risks associated with ocean fertilization are substantial.

One of the primary concerns is the potential for unintended consequences in marine ecosystems. Large-scale phytoplankton blooms could alter food webs in unpredictable ways, potentially harming some species while benefiting others. There is also the risk of creating oxygen-depleted “dead zones” as the phytoplankton die and decompose, consuming oxygen in the process[xii].

The long-term effectiveness of ocean fertilization remains uncertain. While some small-scale experiments have shown promise, the ability to sequester carbon over long periods and the potential for re-release of the captured carbon are still subjects of debate[xiii].

Enhanced Weathering: Accelerating Nature’s Carbon Capture

Enhanced weathering represents a more subtle approach to geoengineering, aiming to accelerate the natural process by which rocks absorb CO2 from the atmosphere. This technique typically involves spreading finely ground rock, such as olivine, over extensive land areas[xiv].

The potential benefits of enhanced weathering are significant. Unlike some other geoengineering approaches, it offers permanent carbon sequestration. The CO2 absorbed through this process is converted into stable carbonate minerals, effectively removing it from the carbon cycle for millions of years. The process can improve soil quality, potentially boosting agricultural productivity.

However, the scale required for meaningful impact is daunting. To remove just 1 billion tons of CO2 per year (about 2.5% of current annual emissions), we would need to spread ground rock over an area roughly the size of Spain[xv]. The energy costs for mining, grinding, and distributing such vast quantities of rock would be substantial, potentially offsetting some of the carbon sequestration benefits.

Direct Air Capture: The Technological Moonshot

While not traditionally considered geoengineering, large-scale deployment of Direct Air Capture (DAC) could have similar global effects. DAC technology removes CO2 directly from the ambient air, offering a way to address emissions from distributed sources like transportation and agriculture[xvi].

The primary advantage of DAC is its precision and verifiability. Unlike other geoengineering approaches, DAC allows for direct measurement of the amount of CO2 removed. It does not come with the same risks of unintended environmental consequences as techniques like SAI or ocean fertilization.

However, current DAC technology faces significant hurdles. It is extremely expensive and energy intensive. A recent analysis suggests that removing enough CO2 to meet climate targets could cost trillions of dollars annually[xvii]. The captured CO2 must be safely stored, typically in underground geological formations, and the readily available capacity for such storage is limited.

Despite these challenges, ongoing research and development might make DAC more viable in the future. Companies like Climeworks in Switzerland and Carbon Engineering in Canada are working to scale up DAC technology, and some experts believe costs could come down significantly with further innovation[xviii].

Governance and Ethical Considerations

The global nature of geoengineering interventions necessitates international cooperation and requires modification of some existing governance structures. The potential for unilateral action by desperate nations poses significant geopolitical risks. Imagine, for instance, a scenario where a country suffering from severe drought deploys SAI that alters weather patterns in neighboring countries or even worldwide[xix].

Reliance on geoengineering could reduce incentives for emissions reductions, creating a moral hazard. If we believe there is a technological fix for climate change, there would be less motivation to make the difficult but necessary changes to energy systems and lifestyles[xx].

We must also grapple with intergenerational ethics. Are we justified in imposing the risks and burdens of geoengineering on future generations? This question becomes poignant when we consider that many geoengineering techniques, once started, would need to be maintained indefinitely to avoid sudden, catastrophic warming[xxi].

Geoengineering Conclusion

In a warming world, geoengineering may indeed become unavoidable. Given the stakes and current trajectory, it would be irresponsible not to research and prepare for potential geoengineering deployments.