Geoengineering

Some types of geoengineering present political, social and ethical issues. One common objection is that focusing on these technologies could undermine efforts to reduce greenhouse gas emissions. Effective governance and international oversight are widely regarded as essential.

Major scientific organizations have examined the potential, risks, and governance needs of geoengineering, including the US National Academies of Sciences, Engineering, and Medicine, the Royal Society, the UN Educational, Scientific and Cultural Organization (UNESCO), and the World Climate Research Programme.

Methods

Carbon dioxide removal

Carbon dioxide removal (CDR) is a process in which carbon dioxide (CO₂) is removed from Earth's atmosphere by deliberate human activities and durably stored in geological, terrestrial, or marine reservoirs, or in products. This process is also known as carbon removal, greenhouse gas removal or negative emissions. CDR is more and more often integrated into climate policy, as an element of climate change mitigation strategies. Achieving net zero emissions will require first and foremost deep and sustained cuts in emissions, and then—in addition—the use of CDR ("CDR is what puts the net into net zero emissions" ). In the future, CDR may be able to counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.

CDR includes methods that are implemented on land or in aquatic systems. Land-based methods include afforestation, reforestation, agricultural practices that sequester carbon in soils (carbon farming), bioenergy with carbon capture and storage (BECCS), and direct air capture combined with storage. There are also CDR methods that use oceans and other water bodies. Those are called ocean fertilization, ocean alkalinity enhancement, wetland restoration and blue carbon approaches. A detailed analysis needs to be performed to assess how much negative emissions a particular process achieves. This analysis includes life cycle analysis and "monitoring, reporting, and verification" (MRV) of the entire process. Carbon capture and storage (CCS) are not regarded as CDR because CCS does not reduce the amount of carbon dioxide already in the atmosphere.

Solar radiation modification

Solar radiation modification (SRM), also called solar geoengineering, is a group of large-scale approaches to reduce global warming by increasing the amount of sunlight that is reflected away from Earth and back to outer space. It is not intended to replace efforts to reduce greenhouse gas emissions, but rather to complement them as a potential way to limit global warming. SRM is a form of geoengineering.

The most-researched SRM method is stratospheric aerosol injection (SAI), in which small reflective particles would be introduced into the upper atmosphere to reflect sunlight. Other approaches include marine cloud brightening (MCB), which would increase the reflectivity of clouds over the oceans, or constructing a space sunshade or a space mirror, to reduce the amount of sunlight reaching earth.

Glacial geoengineering

Glacial geoengineering is a set of proposed geoengineering approaches that focus on slowing the loss of glaciers, ice sheets, and sea ice in polar regions and, in some cases, alpine areas. Proposals are motivated by concerns that feedback loops—such as ice-albedo loss, accelerated glacier flow, and permafrost methane release—could amplify climate change and trigger climate tipping points.

Proposed glacial geoengineering methods include regional or local solar radiation management, thinning cirrus clouds to allow more heat to escape, and deploying mechanical or engineering structures to stabilize ice. Specific strategies under investigation are stratospheric aerosol injection focused on polar regions, marine cloud brightening, surface albedo modification with reflective materials, basal interventions such as draining subglacial water or promoting basal freezing, and ice shelf protection measures including seabed curtains.

Glacial geoengineering is in the early research stage and many proposals face major technical, environmental, and governance challenges. Supporters argue that targeted interventions could help stabilize ice sheets, slow sea-level rise, and reduce the risk of passing irreversible thresholds in the climate system. At the same time, experts caution that the effectiveness of these methods remains highly uncertain and that interventions could produce unintended side effects. Glacial geoengineering is generally considered a possible complement to, not a replacement for, efforts to reduce greenhouse gas emissions.