In 2024, atmospheric concentrations of carbon dioxide reached their highest level in 2 million years. 2024 was also the hottest year in Earth’s recorded history. Hotter than any year in at least 2,000 years, and likely far longer. Absent a radical response, this record will keep breaking with every year to come.
Solar geoengineering (or Solar Radiation Management - SRM) is one of several powerful technologies that have been proposed to limit the most destructive aspect of the climate crisis: global heating. It is a strategy to stabilize the climate, but it would not solve the problem of emissions, which are the source of the problem.
There is little government funded research but also few regulations. This is a fertile ground for anyone – including rogue actors —to seize the idea and experiment without the proper risk assessment. On the other hand, there is a critical gap in communication and processes to ensure transparency, public participation and trust in climate science and research.
As SRM moves rapidly to the forefront a global conversation about what humans can do, must do, or should not do in a planetary emergency has become urgent.
KEY TERMS
Sunlight reflection methods
Sunlight reflection methods or solar radiation modification (SRM) describes a set of ideas to increase the amount of sunlight that the Earth reflects to space. This idea goes by other names – solar geoengineering, solar climate engineering, and solar climate intervention. All SRM approaches would have the same fundamental aim: to offset some of the warming effects of greenhouse gases by rebalancing the Earth’s energy budget.
The Earth reflects around 30% of the light that reaches it. If this could be increased by just one percentage point overall, this could offset around 1°C of global warming.1 (SRM 360)
Termination Shock
The risk of a rapid and dangerous rise in temperatures that scientists predict could result from abruptly stopping a solar geoengineering effort, once deployed.
Marine Cloud Brightening
Marine cloud brightening (MCB) is an idea to enhance the reflectivity of low-lying clouds over the oceans. MCB may be able to produce a large regional cooling effect, but the uneven cooling may lead to large shifts in global rainfall patterns.
Stratospheric Aerosol Injection
Stratospheric aerosol injection (SAI) is an idea to create a layer of tiny reflective particles high in the atmosphere to reflect a small amount of sunlight. In 1991, Mount Pinatubo in the Philippines erupted with a tremendous force, ejecting vast amounts of ash and gas high into the atmosphere; so high that the volcano’s plume penetrated into the stratosphere. There, it formed a thin, global aerosol layer that reflected around 1% of incoming sunlight for roughly a year, acting like a parasol and ever so slightly brightening the sky. Global temperatures dipped by around 0.5°C in the year following Pinatubo’s eruption, an indication of long term temperature reduction possibilities.
Moral Hazard
Broadly defined, a “moral hazard” describes a situation where an individual or institution is more inclined to take risks because they know they are protected from the negative consequences. In the context of solar geoengineering or SRM, a central concern is that the suggestion of a quick, cheap, technological fix to reduce the symptom of global temperature rise will reduce the scale of efforts to cut CO2 emissions, which are the central, driving cause of the rise in the first place.