With the UNEP Emissions Gap Report warning that we are heading for 2.9C above pre-industrial levels, we may need to deploy targeted climate engineering technologies as a “last resort” to avoid the worst excesses of the climate crisis. However, much work remains to be done to create a governance framework that will ensure the benefits and risks are fairly distributed across the globe.
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We know how to solve the climate crisis; we “simply” stop burning fossil fuels. Unfortunately, as the recent UN Climate Change Global Stocktake confirms, to meet the 2015 Paris Agreement we need to cut greenhouse gas emissions by 43% in the next six years, a course of action we appear reluctant and unable to take in such a short time. This begs the question of what other courses of action might be at our disposal when (not if) global temperatures are significantly higher than today. Despite the urgency of the situation, geoengineering, the deliberate intervention in the Earth’s natural systems to counteract climate change remains highly controversial.
While the subject is understandably contentious, there is a growing body of evidence which demonstrates that climate engineering can be highly effective in reducing global temperatures over relatively short timescales. In this article, I explore both sides of the climate engineering divide, and argue that targeted climate engineering should be developed as a matter of urgency as an option of last resort.
Let’s start with a recap of the two main approaches.
The first is greenhouse gas removal, which uses biological and chemical processes to extract carbon dioxide (CO2) from the atmosphere. This can be achieved through tree planting, burying charred biomass – so-called biochar – to lock the carbon into the soil, direct air capture using giant air scrubbers followed by ‘sequestering’ the CO2 underground, enhanced weathering of ground up rocks, or by adding nutrients to oceans to increase primary production leading to a drawdown of carbon from the atmosphere.
The second approach is solar radiation management (SRM), which reduces the rate at which the Earth absorbs energy from the sun. Most development is focused on increasing the planet’s “albedo” to reflect more solar radiation back into space by either releasing reflective particles into the upper atmosphere, mimicking the stratospheric sulphur aerosols often emitted during volcanic eruptions, or by marine cloud brightening, which sprays sea-water into the air to seed low-altitude stratocumulus clouds and increase their brightness.
Two positions currently dominate the current conversation. On one side, many scientists have called for a moratorium on geoengineering as, they argue, its use would only encourage fossil fuel companies to extract more hydrocarbons, thus continuing emissions of greenhouse gases. SRM might also lead to ”termination shock” whereby, should emissions continue to increase while engineering is used, stopping use of the technology would cause even greater disruption to the climate than if the engineering had not been deployed. An “opposing” stance is taken by the fossil fuel industry which continues to vociferously promote Carbon Capture and Storage (CCS).
This, they contend, would render fossil fuels effectively carbon neutral, and, if sequestration rates were high enough, could start to address historical emissions. Tellingly perhaps, the fossil fuel industry does not publicly call for SRM, as it might too clearly give the impression that further extraction is their primary goal.
The two sides of the argument are far from being diametrically opposed, with each often at cross purposes to the other. While most agree that carbon capture could play a key role used in conjunction with a phase-out of fossil fuels, proponents of CCS usually fail to point out that total current CCS capacity represents only 0.1% of global CO2 emissions and will be almost impossible to scale up sufficiently in any reasonable time. The technology is limited by high processing costs which exceed $600 per tonne CO2 captured, compared with the market price of carbon which remains too low to stimulate the adoption of new processes such as CCS.
On the other hand, those wanting a moratorium on the use of climate engineering techniques take their position because there are good reasons to believe that many SRM techniques are highly effective. We have direct evidence, for example, that volcanic emissions of sulphur aerosols have reduced historical global temperatures to levels below what they would have been, and that we can mimic this effect with aerosol injections into the stratosphere. The academic community is highly engaged with modelling the impacts of SRM, the results suggesting that a significant reduction in future global temperatures could be achieved.
At the very least, the state of the current debate highlights the lack of a high-level strategy, one that considers all the available options, together with an assessment of their impacts including social and political dimensions. In The Art of War, and here I’m thinking about the climate crisis on a war footing, Sun Tzu says of strategies, “In battle there are not more than two methods of attack – the direct and the indirect; yet these two in combination gives rise to an unending series of manoeuvres.” By focusing solely on emissions reduction (direct attack), I believe that we are overlooking important approaches that could, if needed, provide emergency manoeuvres. In the light of the recent Stocktake, we have few options left given the diminishing time before our global carbon budget is completely spent.
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It cannot be denied, however, that SRM poses significant global governance issues. Given the uncertainties that remain about the global distribution of the potential cooling and associated changes in rainfall, how would we even design, plan and implement these types of intervention in a globally just manner? In the words of Janoz Pastor, Executive Director of the Carnegie Climate Governance Initiative, “Who assesses the balance of risks and rewards when deploying geoengineering technologies? …If we start deliberately altering global temperatures, who controls the global thermostat?”
The deployment of SRM is no longer a theoretical issue. In 2022, a US startup intentionally released two balloons from Baja California each of which dispersed a few grams of sulphur dioxide particles into the atmosphere. While the amounts were miniscule, this created sufficient concern within the Mexican government for them to issue a statement reiterating their “commitment to the protection and well-being of the population from practices that generate risks to human and environmental security.” While the release was more provocative than impactful, it highlights the rapidly changing attitudes to geoengineering and the lack of formal international agreements. Organisations such as SilverLining and the Climate Overshoot Commission are therefore calling for the acceleration of SRM research to build a consensus about which approaches should be considered and the development of effective governance.
It’s not as if safeguards do not already exist to frame the development of climate interventions. The UN convention on Biological Diversity, for example, states that “no climate-related geo-engineering activities that may affect biodiversity take place, until there is an adequate scientific basis on which to justify such activities and appropriate consideration of the associated risks for the environment.”
What is frustrating is that this convention is not invoked to prevent the greenhouse gas emissions which already threaten the Earth’s biodiversity. While rightly cautious, we appear to have an innate bias against intentional environmental interventions, despite our concern about the unintended consequences of burning fossil fuels. Geoengineering therefore presents us with a fundamental moral question of whether it is preferable to risk doing harm in attempting to do good than to allow continuing harm through inaction. Fortunately, into this debate comes a new approach, one which may allay some concerns about direct climate interventions. This is the use of targeted climate engineering, which addresses climate breakdown at the regional level with particular focus on the cryosphere (sea ice, permafrost, and ice sheets).
Potential solutions being considered range from the use of glass beads to increase the reflectiveness of Arctic ice to the introduction of large herbivores to reduce foliage and trample the snow and cool the permafrost; a pilot scheme in East Siberia has already been fenced and stocked with bison, musk ox, reindeer and much of the taiga removed. Marine cloud brightening can also be deployed using a semi-targeted approach. Not only does this method use “innocuous aerosols […] salty droplets extracted from the ocean and sprayed into the air by autonomous sailboats.” Any perceived risks are tempered by the fact that, until the recent reduction of sulphur in bunker shipping fuels, maritime traffic was already seeding cloud formation along shipping lanes – as can be seen in the image below.
Ship tracks seen in the Pacific from the Suomi NPP satellite, December 2021. Photo: NASA.
To conclude, I believe that we have arrived at such a critical juncture in the climate crisis that we should “leave no stone unturned” in the development of effective multimodal responses. With the UNEP Emissions Gap Report warning that we are heading for 2.9C above pre-industrial levels, we urgently need to widen the spectrum of remedial actions to include climate engineering; to be deployed alongside, not in place of, the rapid phase-out of fossil fuels. To do this we will need to be highly creative in developing new engineering manoeuvres, scientifically rigorous to assess the myriad of impacts, and socially just to ensure we distribute the benefits and risks fairly across the globe. But more than anything, we will need to be courageous by being fully cognisant, intentional, and responsible for our collective actions.
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