Rapid decarbonization remains fundamental to limiting the global mean temperature rise to well below 2°C, as outlined in the 2015 Paris Agreement [1]. Yet, as climate impacts intensify, geoengineering is increasingly portrayed as an alternative, or complement, to mitigation [2].
What is geoengineering?
The IPCC defines geoengineering as ‘a broad set of methods and technologies that aim to deliberately alter the climate system in order to alleviate the impacts of climate change.’ [6] It recognises two broad categories of geoengineering: carbon dioxide removal (CDR) and solar radiation management (SRM).
CDR involves techniques that remove carbon dioxide directly from the atmosphere. This includes large-scale afforestation, bioenergy with carbon capture and storage (BECCS), as well as iron fertilization in the ocean [7].
SRM’s goal is to lower the Earth’s surface temperature by reflecting more sunlight away from the Earth, thereby reducing the amount of solar radiation that reaches the planet. It commonly works by altering the albedo (reflexivity) of different surfaces. For example, ground-based albedo modifications (GBAM) can be as simple as painting rooftops white. Other forms of SRM involve releasing reflective particles into the atmosphere and increasing cloud reflectivity, such as stratospheric aerosol interventions (SAI) and marine cloud brightening (MCB) [1].
Other emerging approaches include methane removal, infrared radiation management (IRM), and glacial geoengineering [7].
An effective climate solution?
No single geoengineering technology can, on its own, achieve the Paris Agreement’s targets [1]. Their effectiveness varies greatly between and within categories.
Carbon dioxide removal
Afforestation and reforestation are relatively low-cost, well-understood options that can store carbon for decades to centuries. By contrast, carbon capture and storage (CCS) operates on timescales of 10,000+ years, but remains costly and complex [1, 8].
For example, the Australian Gorgon project cost an estimated $54 billion dollars but has consistently failed to meet its target of storing 80% of the CO₂ produced during gas extraction. In 2023-2024, it captured just 1.6 of the 5.3 million tonnes produced that year [9, 11]. Researchers suggest that a ‘high-CCS’ pathway to net zero by 2050 could cost $30 trillion more than a ‘low-CCS’ pathway, or roughly $1 trillion per year [11, 12].
There is also a non-negligible chance that CCS fails to be deployed at scale [11].
Solar radiation management
SRM technology is highly novel. Even the most researched form – SAI – is limited to modelling and small-scale experiments [1]. Scenarios suggest deployment could begin in the polar regions by 2040, or globally by 2060 [2].
While SAI has an extremely high potential to mitigate warming, it is also more expensive than previously thought, requiring $16.7 billion US dollars’ worth of aircraft and infrastructure and $1 billion US dollars annually [2]. It also carries human and environmental risks, including ozone depletion and regional disruptions to precipitation. Governance and ethical issues, such as transboundary impacts, and transgenerational risk, remain unresolved [2].
Geoengineering vs mitigation
By contrast, conventional mitigation options like renewable energy and ecosystem restoration are cheaper, safer, and already scalable. According to the IPCC, the cost of avoiding one tonne of CO₂ by 2030 is approximately under $20 for solar and wind, compared to up to $200 for CCS [1]. Renewable technologies also reduce emissions immediately, while geoengineering would take decades to deploy effectively.
Other ‘low-tech, win-win’ approaches to mitigation include restoring forest, grassland, and peat ecosystems. These approaches also have other benefits such as increasing wildlife diversity and improving the resilience of local communities [13].
Near-term mitigation significantly reduces the risk of overshooting 1.5°C, transitional challenges and the need for future reliance on CDR [13].
Technological optimism
Given the high cost, risks, and uncertainties regarding geoengineering, it is important to question why this technology has received so much attention and funding in recent years.
According to Lamb, William F et. al, this enthusiasm can be termed technological optimism, ‘holding that technological progress will rapidly bring about emissions reductions in the future’; though science suggests that geoengineering alone is unlikely to bring large-scale reductions in carbon emissions without significant technological advancement [14].
This discourse delays effective climate action and justifies continued fossil fuel dependence. This follows what researchers describe as ‘predatory delay’: deliberate efforts by powerful institutions to slow the implementation of actions that address the root causes of problems to preserve their own financial and political power [15]. By funding geoengineering research and promoting it as a tool to buy time for decarbonization, fossil fuel companies and philanthrocapitalists can protect their own interests [15].
Conclusion
Geoengineering alone is not an effective climate solution or a substitute for mitigation, given limitations in feasibility, scale and cost [1]. Even advanced forms like CCS, which have been in use for decades, may not work reliably at a large scale. While CCS could play a minor role in offsetting emissions – and could be of great help in eliminating residual emissions (those which are already in our atmosphere) – it is not by itself an effective climate solution [16].
To meet the Paris Agreement targets and keep warming below 2°C, mitigation must remain the priority. Geoengineering should be pursued cautiously without diverting resources from mitigation, and technological optimism should be critically examined.
