Geoengineering, also called climate engineering or climate intervention, refers to planned large actions taken to help reduce the effects of climate change caused by humans. This area includes two main types: large-scale carbon dioxide removal (CDR) and solar radiation modification (SRM). CDR uses methods to take carbon dioxide out of the air and is usually seen as a way to reduce the effects of climate change. SRM works by reflecting a small amount of sunlight away from Earth back into space to lower global warming. Even though they were once grouped together, these methods are very different in how they work, how long they take, and the risks they may cause. They are now usually discussed separately. Other large projects, such as actions to slow the melting of ice in polar and alpine regions, are sometimes considered forms of geoengineering.
Some geoengineering ideas raise political, social, and ethical concerns. A common worry is that relying on these technologies might reduce efforts to cut greenhouse gas emissions. Many experts believe that strong rules and international agreements are very important to manage these technologies properly. Major scientific groups, 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, have studied the possibilities, risks, and rules needed for geoengineering.
Methods
Carbon dioxide removal (CDR) is a process where carbon dioxide (CO₂) is taken from Earth's atmosphere through human actions and stored safely in places like rocks, soil, oceans, or products. This process is also called carbon removal, greenhouse gas removal, or negative emissions. CDR is increasingly used in climate policies as part of plans to reduce climate change. To reach net zero emissions, the most important step is to greatly and continuously reduce emissions. Then, CDR can help balance emissions that are hard to eliminate, such as some emissions from farming and industry.
CDR includes methods done on land or in water. Land-based methods include planting trees, improving farming to store carbon in soil, using bioenergy with carbon capture and storage (BECCS), and capturing CO₂ directly from the air and storing it. Methods using oceans and water include adding nutrients to oceans, making ocean water more alkaline, restoring wetlands, and protecting coastal ecosystems that store carbon. To determine how much CO₂ a method removes, scientists analyze the process’s life cycle and monitor, report, and verify the results. Carbon capture and storage (CCS) is not considered CDR because it does not remove CO₂ already in the atmosphere.
Solar radiation modification (SRM), also called solar geoengineering, is a group of large-scale methods to reduce global warming by reflecting more sunlight back into space. SRM is not meant to replace efforts to cut greenhouse gas emissions but can help limit warming when used alongside these efforts. SRM is a type of geoengineering.
The most studied SRM method is stratospheric aerosol injection (SAI), which involves spraying tiny reflective particles into the upper atmosphere to reflect sunlight. Other methods include making ocean clouds more reflective and building space structures to block sunlight.
Glacial geoengineering includes proposed methods to slow the melting of glaciers, ice sheets, and sea ice in polar and mountain regions. These ideas aim to address concerns that melting ice could worsen climate change through feedback loops, such as less sunlight being reflected and more methane being released.
Proposed methods for glacial geoengineering include managing sunlight in specific areas, thinning clouds to let more heat escape, and using engineering tools to support ice. Examples include spraying particles in polar regions, making ocean clouds more reflective, covering surfaces with reflective materials, and building structures to protect ice shelves.
Glacial geoengineering is still in early research stages and faces many technical, environmental, and governance challenges. Supporters believe it could help slow ice loss and reduce risks of irreversible climate changes. However, experts warn that its effectiveness is uncertain and that it might cause unexpected problems. Glacial geoengineering is seen as a possible addition to, not a replacement for, efforts to reduce greenhouse gas emissions.
Governance
Most issues about managing geoengineering depend on the type of method used. However, a few international agreements have discussed geoengineering as a whole.
The Conference of Parties to the Convention on Biological Diversity made several decisions about "climate-related geoengineering." In 2010, they created a detailed set of guidelines that are not legally required for "climate-related geoengineering activities that may affect biodiversity." These guidelines require such activities to be supported by specific scientific data, undergo environmental evaluations, and be monitored by regulatory systems. In 2016, the Parties encouraged more research that combines different fields and sharing of knowledge to better understand the effects of climate-related geoengineering.
The parties to the London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter and its related London Protocol discussed "marine geoengineering." In 2013, the parties to the London Protocol adopted an amendment to create a set of rules that must be followed for regulating marine geoengineering, initially limited to ocean fertilization. This rule required evaluations and approvals before any activity could begin. This amendment has not yet become active because not enough countries agreed to it. In 2022, the parties to both agreements recognized growing interest in marine geoengineering, listed four techniques for review, and encouraged careful evaluations of proposed projects using existing guidelines while considering further rules. In 2023, they warned that these techniques might cause serious environmental problems, pointed out that scientists do not fully understand their effects, emphasized the need to strictly follow evaluation rules, and called for more global teamwork. Their work is supported by the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection of the International Maritime Organization.