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Sunday, July 26, 2026

Disinformation

From Wikipedia, the free encyclopedia

Disinformation is false or misleading information deliberately spread to deceive people, or to secure economic or political gain and which may cause public harm. Disinformation is an orchestrated adversarial activity in which actors employ strategic deceptions and media manipulation tactics to advance political, military, or commercial goals. Disinformation is implemented through coordinated campaigns that "weaponize multiple rhetorical strategies and forms of knowing—including not only falsehoods but also truths, half-truths, and value judgements—to exploit and amplify culture wars and other identity-driven controversies."

In contrast, misinformation refers to inaccuracies that stem from inadvertent error. Misinformation can be used to create disinformation when known misinformation is purposefully and intentionally disseminated. "Fake news" has sometimes been categorized as a type of disinformation, although scholars distinguish between the two concepts. Some researchers have cautioned against using the term in academic writing have because of its lack of precision and its contested use in public and political discourse regarding news coverage or information. Others note that it continues to be used both in reference to demonstrably false or misleading information and more broadly in political communication, where its meaning and implications remain debated.

Etymology

The Etymology of Disinformation by H. Newman as published in The Journal of Information Warfare in 2021. Elements of the word disinformation have their origins in Proto-Indo-European language family. The Latin 'dis' and 'in' and can both be considered to have Proto-Indo-European roots, 'forma' is considerably more obscure. The green box in the figure highlights the origin 'forma' is uncertain, however, it may have its roots in the Aristotelian concept of μορφή (morphe) where something becomes a 'thing' when it has 'form' or substance.

The English word disinformation comes from the application of the Latin prefix dis- to information making the meaning "reversal or removal of information". The rarely used word had appeared with this usage in print at least as far back as 1887. Some consider it a loan translation of the Russian дезинформация, transliterated as dezinformatsiya, apparently derived from the title of a KGB black propaganda department. Soviet planners in the 1950s defined disinformation as "dissemination (in the press, on the radio, etc.) of false reports intended to mislead public opinion."

Disinformation first made an appearance in dictionaries in 1985, specifically, Webster's New College Dictionary and the American Heritage Dictionary. In 1986, the term disinformation was not defined in Webster's New World Thesaurus or New Encyclopædia Britannica. After the Soviet term became widely known in the 1980s, native speakers of English broadened the term as "any government communication (either overt or covert) containing intentionally false and misleading material, often combined selectively with true information, which seeks to mislead and manipulate either elites or a mass audience."

By 1990, use of the term disinformation had fully established itself in the English language within the lexicon of politics. By 2001, the term disinformation had come to be known as simply a more civil phrase for saying someone was lying. Stanley B. Cunningham wrote in his 2002 book The Idea of Propaganda that disinformation had become pervasively used as a synonym for propaganda.

Operationalization

The Shorenstein Center at Harvard University defines disinformation research as an academic field that studies "the spread and impacts of misinformation, disinformation, and media manipulation", including "how it spreads through online and offline channels, and why people are susceptible to believing bad information, and successful strategies for mitigating its impact". According to a 2023 research article published in New Media & Society, disinformation circulates on social media through deception campaigns implemented in multiple ways including: astroturfing, conspiracy theories, clickbait, culture wars, echo chambers, hoaxes, fake news, propaganda, pseudoscience, and rumors.

Glossary of key terms related to disinformation and misinformation
Term Description Term Description
Astroturfing A centrally coordinated campaign that mimics grassroots activism by making participants pretend to be ordinary citizens Fake news Genre: The deliberate creation of pseudo-journalism

Label: The instrumentalization of the term to delegitimize news media

Conspiracy theories Rebuttals of official accounts that propose alternative explanations in which individuals or groups act in secret Greenwashing Deceptive communication makes people believe that a company is environmentally responsible when it is not
Clickbait The deliberate use of misleading headlines and thumbnails to increase online traffic for profit or popularity Propaganda Organized mass communication, on a hidden agenda, and with a mission to conform belief and action by circumventing individual reasoning
Culture wars A phenomenon in which multiple groups of people, who hold entrenched values, attempt to steer public policy contentiously Pseudoscience Accounts that claim the explanatory power of science, borrow its language and legitimacy but diverge substantially from its quality criteria
Doxxing A form of online harassment that breaches privacy boundaries by releasing information intending physical and online harm to a target Rumors Unsubstantiated news stories that circulate while not corroborated or validated
Echo chamber An epistemic environment in which participants encounter beliefs and opinions that coincide with their own Trolling Networked groups of digital influencers that operate 'click armies' designed to mobilize public sentiment
Hoax News in which false facts are presented as legitimate Urban legends Moral tales featuring durable stories of intruders incurring boundary transgressions and their dire consequences

In order to distinguish between similar terms, including misinformation and malinformation, scholars collectively agree on the definitions for each term as follows: (1) disinformation is the strategic dissemination of false information with the intention to cause public harm; (2) misinformation represents the unintentional spread of false information; and (3) malinformation is factual information disseminated with the intention to cause harm, these terms are abbreviated 'DMMI'.

In 2019, Camille François devised the "ABC" framework of understanding different modalities of online disinformation:

In 2020, the Brookings Institution proposed amending this framework to include Distribution, defined by the "technical protocols that enable, constrain, and shape user behavior in a virtual space". Similarly, the Carnegie Endowment for International Peace proposed adding Degree ("distribution of the content ... and the audiences it reaches") and Effect ("how much of a threat a given case poses").

Comparisons with propaganda

Whether and to what degree disinformation and propaganda overlap is subject to debate. Some (like U.S. Department of State) define propaganda as the use of non-rational arguments to either advance or undermine a political ideal, and use disinformation as an alternative name for undermining propaganda, while others consider them to be separate concepts altogether. One popular distinction holds that disinformation also describes politically motivated messaging designed explicitly to engender public cynicism, uncertainty, apathy, distrust, and paranoia, all of which disincentivize citizen engagement and mobilization for social or political change.

Practice

Disinformation is the label often given to foreign information manipulation and interference (FIMI). Studies on disinformation are often concerned with the content of activity whereas the broader concept of FIMI is more concerned with the "behaviour of an actor" that is described through the military doctrine concept of tactics, techniques, and procedures (TTPs).

Disinformation is primarily carried out by government intelligence agencies, but has also been used by non-governmental organizations and businesses. Front groups are a form of disinformation, as they mislead the public about their true objectives and who their controllers are. Most recently, disinformation has been deliberately spread through social media in the form of "fake news", disinformation masked as legitimate news articles and meant to mislead readers or viewers. Disinformation may include distribution of forged documents, manuscripts, and photographs, or spreading dangerous rumours and fabricated intelligence. Use of these tactics can lead to blowback, however, causing such unintended consequences such as defamation lawsuits or damage to the dis-informer's reputation.

Disinformation can spread with greater ease in situations where there is a lack of credible information on a topic, such as a crisis. The implications of this were seen after the 2024 Southport stabbings, where the spread of disinformation regarding the killer's background was fuelled by reporting restrictions, meaning that there were no facts to counter the disinformation. This then led to the 2024 United Kingdom riots.

Worldwide

Disinformation has been identified as a significant challenge, undermining public trust and the factual basis for public debate. Studies have found that false information often spreads faster and more widely online than accurate information. Empirical research has also links disinformation to political polarisation, democratic erosion, and regime resilience in authoritarian contexts.

Soviet disinformation

Ion Mihai Pacepa.
Former Romanian secret police senior official Ion Mihai Pacepa exposed disinformation history in his book Disinformation (2013).

Use of disinformation as a Soviet tactical weapon started in 1923, when it became a tactic used in the Soviet political warfare called active measures.

Russian disinformation

Russian disinformation campaigns have occurred in many countries. For example, disinformation campaigns led by Yevgeny V. Prigozhin, a Russian oligarch, have been reported in several African countries. Russia denies that it uses disinformation to influence public opinion. Often Russian campaigns aim to disrupt domestic politics within Europe and the United States in an attempt to weaken the West due to its long-standing commitment to fight back against "Western imperialism" and shift the balance of world power to Russia and its allies (the Second World during the Cold War era). According to the Voice of America, Russia seeks to promote American isolationism, border security concerns and racial tensions within the United States through its disinformation campaigns.

Chinese disinformation

Spamouflage (also known under the names Dragonbridge, Spamouflage Dragon, Storm 1376 and Taizi Flood) is an online propaganda and disinformation operation that has been using a network of social media accounts to make posts in favor of the Chinese Communist Party and government of the People's Republic of China and harass dissidents and journalists overseas since 2017. Beginning in the early 2020s, Spamouflage accounts also began making posts about American and Taiwanese politics. It is widely believed that the Chinese government, particularly the Ministry of Public Security, is behind the network. Spamouflage has increasingly used generative artificial intelligence for influence operations. The campaign has largely failed to receive views from real users, although it has attracted some organic engagement using new tactics.

American disinformation

How Disinformation Can Be Spread, explanation by U.S. Defense Department (2001)

The United States Intelligence Community appropriated use of the term disinformation in the 1950s from the Russian dezinformatsiya, and began to use similar strategies, starting during Cold War, and in conflict with other nations. The New York Times reported in 2000 that during the CIA's effort to substitute Mohammed Reza Pahlavi for then-Prime Minister of Iran Mohammad Mossadegh, the CIA placed fictitious stories in the local newspaper. Reuters documented how, subsequent to the 1979 Soviet Union invasion of Afghanistan during the Soviet–Afghan War, the CIA put false articles in newspapers of Islamic-majority countries, inaccurately stating that Soviet embassies had "invasion day celebrations". Reuters noted a former U.S. intelligence officer said they would attempt to gain the confidence of reporters and use them as secret agents, to affect a nation's politics by way of their local media.

In October 1986, the term gained increased currency in the U.S. when it was revealed that two months previously, the Reagan Administration had engaged in a disinformation campaign against then-leader of Libya Muammar GaddafiWhite House representative Larry Speakes said reports of a planned attack on Libya as first broken by The Wall Street Journal on August 25, 1986, were "authoritative", and other newspapers including The Washington Post then wrote articles saying this was factual. U.S. State Department representative Bernard Kalb resigned from his position in protest over the disinformation campaign, and said: "Faith in the word of America is the pulse beat of our democracy."

The executive branch of the Reagan administration kept watch on disinformation campaigns through three yearly publications by the Department of State: Active Measures: A Report on the Substance and Process of Anti-U.S. Disinformation and Propaganda Campaigns (1986); Report on Active Measures and Propaganda, 1986–87 (1987); and Report on Active Measures and Propaganda, 1987–88 (1989).

According to a report by Reuters, the United States ran a propaganda campaign to spread disinformation about the Sinovac Chinese COVID-19 vaccine, including using fake social media accounts to spread the disinformation that the Sinovac vaccine contained pork-derived ingredients and was therefore haram under Islamic law. Reuters said the ChinaAngVirus disinformation campaign was designed to "counter what it perceived as China's growing influence in the Philippines" and was prompted by the "[fear] that China's COVID diplomacy and propaganda could draw other Southeast Asian countries, such as Cambodia and Malaysia, closer to Beijing". The campaign was also described as "payback for Beijing's efforts to blame Washington for the pandemic". The campaign primarily targeted people in the Philippines and used a social media hashtag for "China is the virus" in Tagalog. The campaign ran from 2020 to mid-2021. The primary contractor for the U.S. military on the project was General Dynamics IT, which received $493 million for its role.

Since 2023, Republican members of the US Congress have attacked researchers who study disinformation as being against freedom of speech and as a euphemism for government censorship. On April 18, 2025, citing an Executive Order signed by Trump, the US National Science Foundation released a statement cancelling funding for disinformation research, saying that it does not fit with the NSF priorities, "including but not limited to those on diversity, equity, and inclusion (DEI) and misinformation/disinformation."

Disinformation in the 2016 United Kingdom European Union membership referendum

The 2016 United Kingdom European Union membership referendum saw figures from the Leave campaign spread disinformation on social media. Many of these arguments played on voters' emotions and attachments, such as the claim that the £350 million that the UK sent to the EU each week could be allocated to the NHS instead, which made them highly effective. Ofcom requires news broadcasters to remain neutral, yet this adherence to neutrality created false balance in the Brexit debate, causing broadcasters to inadvertedly promote disinformation.

Response

Responses from cultural leaders

Pope Francis condemned disinformation in a 2016 interview, after being made the subject of a fake news website during the 2016 U.S. election cycle which falsely claimed that he supported Donald Trump. He stated that the worst thing the news media could do was spread disinformation and said the act was a sin, comparing those who spread disinformation to individuals who engage in coprophilia.

Ethics in warfare

In a contribution to the 2014 book Military Ethics and Emerging Technologies, writers David Danks and Joseph H. Danks discuss the ethical implications in using disinformation as a tactic during information warfare. They note there has been a significant degree of philosophical debate over the issue as related to the ethics of war and use of the technique. The writers describe a position whereby the use of disinformation is occasionally allowed, but not in all situations. Typically the ethical test to consider is whether the disinformation was performed out of a motivation of good faith and acceptable according to the rules of war. By this test, the tactic during World War II of putting fake inflatable tanks in visible locations on the Pacific Islands in order to falsely present the impression that there were larger military forces present would be considered as ethically permissible. Conversely, disguising a munitions plant as a healthcare facility in order to avoid attack would be outside the bounds of acceptable use of disinformation during war.

Research

Disinformation spreads through controversies.

Research related to disinformation studies is increasing as an applied area of inquiry. The call to formally classify disinformation as a cybersecurity threat is made by advocates due to its increase in social networking sites. Despite the proliferation of social media websites, Facebook and Twitter showed the most activity in terms of active disinformation campaigns. Techniques reported on included the use of bots to amplify hate speech, the illegal harvesting of data, and paid trolls to harass and threaten journalists.

Whereas disinformation research focuses primarily on how actors orchestrate deceptions on social media, primarily via fake news, new research investigates how people take what started as deceptions and circulate them as their personal views. As a result, research shows that disinformation can be conceptualized as a program that encourages engagement in oppositional fantasies (i.e., culture wars), through which disinformation circulates as rhetorical ammunition for never-ending arguments. As disinformation entangles with culture wars, identity-driven controversies constitute a vehicle through which disinformation disseminates on social media. This means that disinformation thrives, not despite raucous grudges but because of them. The reason is that controversies provide fertile ground for never-ending debates that solidify points of view.

Scholars have pointed out that disinformation is not only a foreign threat as domestic purveyors of disinformation are also leveraging traditional media outlets such as newspapers, radio stations, and television news media to disseminate false information. Current research suggests right-wing online political activists in the United States may be more likely to use disinformation as a strategy and tactic. The 2016 European Union referendum in the UK also saw British politicians supporting the Leave campaign spread disinformation on Twitter. The Conservative Party was also accused of spreading disinformation about the Labour Party in the lead-up to the 2019 General Election. Governments have responded with a wide range of policies to address concerns about the potential threats that disinformation poses to democracy, however, there is little agreement in elite policy discourse or academic literature as to what it means for disinformation to threaten democracy, and how different policies might help to counter its negative implications.

Consequences of exposure to disinformation online

There is a broad consensus amongst scholars that there is a high degree of disinformation, misinformation, and propaganda online; however, it is unclear to what extent such disinformation has on political attitudes in the public and, therefore, political outcomes. This conventional wisdom has come mostly from investigative journalists, with a particular rise during the 2016 U.S. election: some of the earliest work came from Craig Silverman at Buzzfeed News. Cass Sunstein supported this in #Republic, arguing that the internet would become rife with echo chambers and informational cascades of misinformation leading to a highly polarized and ill-informed society. Later studies have since proven the existence of echo chambers on social media.

Research after the 2016 US presidential election found: (1) for 14% of Americans social media was their "most important" source of election news; 2) known false news stories "favoring Trump were shared a total of 30 million times on Facebook, while those favoring Clinton were shared 8 million times"; 3) the average American adult saw fake news stories, "with just over half of those who recalled seeing them believing them"; and 4) people are more likely to "believe stories that favor their preferred candidate, especially if they have ideologically segregated social media networks." Correspondingly, whilst there is wide agreement that the digital spread and uptake of disinformation during the 2016 election was massive and very likely facilitated by foreign agents, there is an ongoing debate on whether all this had any actual effect on the election. For example, a double blind randomized-control experiment by researchers from the London School of Economics (LSE), found that exposure to online fake news about either Trump or Clinton had no significant effect on intentions to vote for those candidates. Researchers who examined the influence of Russian disinformation on Twitter during the 2016 US presidential campaign found that exposure to disinformation was (1) concentrated among a tiny group of users, (2) primarily among Republicans, and (3) eclipsed by exposure to legitimate political news media and politicians. Finally, they find "no evidence of a meaningful relationship between exposure to the Russian foreign influence campaign and changes in attitudes, polarization, or voting behavior." As such, despite its mass dissemination during the 2016 Presidential Elections, online fake news or disinformation probably did not cost Hillary Clinton the votes needed to secure the presidency.

Research on this topic remains inconclusive, for example, misinformation appears not to significantly change political knowledge of those exposed to it. There seems to be a higher level of diversity of news sources that users are exposed to on Facebook and Twitter than conventional wisdom would dictate, as well as a higher frequency of cross-spectrum discussion. Other evidence has found that disinformation campaigns rarely succeed in altering the foreign policies of the targeted states.

Research is also challenging because disinformation is meant to be difficult to detect and some social media companies have discouraged outside research efforts. For example, researchers found disinformation made "existing detection algorithms from traditional news media ineffective or not applicable...[because disinformation] is intentionally written to mislead readers...[and] users' social engagements with fake news produce data that is big, incomplete, unstructured, and noisy." Facebook, the largest social media company, has been criticized by analytical journalists and scholars for preventing outside research of disinformation.

Alternative perspectives and critiques

Researchers have criticized the framing of disinformation as being limited to technology platforms, removed from its wider political context and inaccurately implying that the media landscape was otherwise well-functioning. "The field possesses a simplistic understanding of the effects of media technologies; overemphasizes platforms and underemphasizes politics; focuses too much on the United States and Anglocentric analysis; has a shallow understanding of political culture and culture in general; lacks analysis of race, class, gender, and sexuality as well as status, inequality, social structure, and power; has a thin understanding of journalistic processes; and, has progressed more through the exigencies of grant funding than the development of theory and empirical findings."

Alternative perspectives have been proposed:

  1. Moving beyond fact-checking and media literacy to study a pervasive phenomenon as something that involves more than news consumption.
  2. Moving beyond technical solutions including AI-enhanced fact checking to understand the systemic basis of disinformation.
  3. Develop a theory that goes beyond Americentrism to develop a global perspective, understand cultural imperialism and Third World dependency on Western news, and understand disinformation in the Global South.
  4. Develop market-oriented disinformation research that examines the financial incentives and business models that nudge content creators and digital platforms to circulate disinformation online.
  5. Include a multidisciplinary approach, involving history, political economy, ethnic studies, feminist studies, and science and technology studies.
  6. Develop understandings of Gendered-based disinformation (GBD) defined as "the dissemination of false or misleading information attacking women (especially political leaders, journalists and public figures), basing the attack on their identity as women."

Strategies for spreading disinformation

Disinformation attack

The research literature on how disinformation spreads is growing. Studies show that disinformation spread in social media can be classified into two broad stages: seeding and echoing. "Seeding", when malicious actors strategically insert deceptions, like fake news, into a social media ecosystem, and "echoing" is when the audience disseminates disinformation argumentatively as their own opinions often by incorporating disinformation into a confrontational fantasy.

Internet manipulation

Separate from factual reporting, techniques such as rage baiting, outrage porn, etc. involve media broadcast of content designed to manipulate increased viewer engagement, often by provoking negative emotional responses aligned with political or other narratives.

Internet manipulation is the use of online digital technologies, including algorithms, social bots, and automated scripts, for commercial, social, military, or political purposes. Internet and social media manipulation are the prime vehicles for spreading disinformation due to the importance of digital platforms for media consumption and everyday communication. When employed for political purposes, internet manipulation may be used to steer public opinion, polarise citizens, circulate conspiracy theories, and silence political dissidents. Internet manipulation can also be done for profit, for instance, to harm corporate or political adversaries and improve brand reputation. Internet manipulation is sometimes also used to describe the selective enforcement of Internet censorship or selective violations of net neutrality.

Internet manipulation for propaganda purposes with the help of data analysis and internet bots in social media is called computational propaganda.

Studies show four main methods of seeding disinformation online:

  1. Selective censorship
  2. Manipulation of search rankings
  3. Hacking and releasing
  4. Directly sharing disinformation

Recently, concerns have been expressed that AI technology could enable groups of AI programs, known as 'AI swarms,' to autonomously coordinate to manipulate democratic discourse, by maintaining persistent fake identities and mimicking human social dynamics over extended periods of time.

Exploiting online advertising technologies

Disinformation is amplified online due to malpractice concerning online advertising, especially the machine-to-machine interactions of real-time bidding systems. Online advertising technologies have been used to amplify disinformation due to the financial incentives and monetization of user-generated content and fake news. The lax oversight over the online advertising market can be used to amplify disinformation, including the use of dark money used for political advertising.

Saturday, July 25, 2026

Stratospheric aerosol injection

Solar radiation reduction due to volcanic eruptions, considered the best analogue for stratospheric aerosol injection.

Stratospheric aerosol injection (SAI) is a proposed method of solar geoengineering (or solar radiation modification) to reduce global warming. This would introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic winter. It has been claimed that stratospheric aerosol injection, at a moderate intensity, could counter most changes to temperature and precipitation, take effect rapidly, have low direct implementation costs, and be reversible in its direct climatic effects. The Intergovernmental Panel on Climate Change concludes that it "is the most-researched solar radiation modification method, with high agreement that it could limit warming to below 1.5 °C (2.7 °F)." However, like other solar geoengineering approaches, stratospheric aerosol injection would do so imperfectly and other effects are possible, particularly if used in a suboptimal manner.

Various forms of sulfur have been shown to cool the planet after large volcanic eruptions. However, as of 2021, there has been little research and existing aerosols in the stratosphere are not well understood, so there is no leading candidate material. Alumina, calcite and salt are also under consideration. The leading proposed method of delivery is custom aircraft.

Background and mechanism

photograph of heavy mist
Mist and fog are aerosols

An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be generated from natural or human causes. The scientific term aerosol refers to the mixture of particulates in gas, and not to the particulate matter alone. The liquid or solid particles in an aerosol have diameters typically less than 1 μm. Larger particles with a significant settling speed make the mixture a suspension, although the distinction is not clear.

Examples of natural aerosols are fog, mist, and dust from geological or biological sources. Certain infections spread by means of small droplets in the breath, sometimes called bioaerosols. Several types of atmospheric aerosol have a significant effect on Earth's climate: volcanic, desert dust, sea-salt, originating from biogenic sources and human-made. Volcanic aerosol forms in the stratosphere after an eruption as droplets of sulfuric acid that can prevail for up to two years, and reflect sunlight, lowering temperature. Desert dust, mineral particles blown to high altitudes, absorb heat and may be responsible for inhibiting storm cloud formation.

Natural aerosols

Sources of natural aerosols include oceans, volcanoes, deserts, and living organisms. The ocean produces aerosols in two main ways. First, when wind blows over waves, it creates spray made up mostly of sea salt. Second, tiny ocean organisms—such as plankton—release dimethyl sulfide and other gases into the air which, in turn, react with other substances in the atmosphere, including water vapor, to form gaseous sulfate (sulfuric acid) aerosols. Both sea salt and sulfate aerosols help to form clouds by acting as "seeds" for water droplets, affecting cloud formation and Earth's energy balance.. While these ocean aerosols are widespread, there is still uncertainty about exactly how much they affect the atmosphere.

Volcanic eruptions release ash and gases into the air. Although the ash falls out of the atmosphere relatively quickly, sulfur dioxide can rise into the stratosphere, where it reacts with water vapor to form long-lived sulfate aerosols in the upper atmosphere. These reflect sunlight and temporarily cool the planet. After a large eruption, these particles can stay in the air for a year or more.

Natural aerosols cool the Earth. When large volcanic eruptions occur, they can cause short-term global cooling of around half a degree or more, depending on the size of the eruption. For example, the eruption of Mount Pinatubo in 1991 caused global temperatures to drop by about 0.5 degrees Celsius for up to three years. These events have played an important role in past climate variability.

Anthropogenic aerosols

Human activities, especially fossil fuel combustion and biomass burning, emit aerosols directly and indirectly via gases that react in the atmosphere. Common anthropogenic aerosols include sulfates, nitrates, black carbon (soot), and organic carbon. Among these, sulfates are the dominant cooling agent. Organic carbon aerosols also reflect light, while black carbon absorbs it, warming the air and darkening snow and ice.

The net effect of anthropogenic aerosols has been to mask global warming. From 1850 to 2014, they reduced global average surface temperature by about 0.66 °C. This cooling is stronger in the more populous Northern Hemisphere. This uneven effect has altered rainfall patterns, including a weakening of tropical monsoons.

Air pollution regulations have reduced sulfate emissions in Europe and North America since the 1980s, and more recently in China. These reductions have improved air quality but diminish the cooling influence of aerosols, contributing to accelerated warming.

History

Mikhail Budyko is believed to have been the first, in 1974, to put forth the concept of artificial solar radiation management with stratospheric sulfate aerosols if global warming ever became a pressing issue. Such controversial climate engineering proposals for global dimming have sometimes been called a "Budyko Blanket".

In 2009, a Russian team tested aerosol formation in the lower troposphere using helicopters. In 2015, David Keith and Gernot Wagner described a potential field experiment, the Stratospheric Controlled Perturbation Experiment (SCoPEx), using stratospheric calcium carbonate injection, but as of October 2020 the time and place had not yet been determined. SCoPEx is in part funded by Bill GatesSir David King, a former chief scientific adviser to the government of the United Kingdom, stated that SCoPEX and Gates' plans to dim the sun with calcium carbonate could have disastrous effects.

In 2012, the Bristol University-led Stratospheric Particle Injection for Climate Engineering (SPICE) project planned on a limited field test to evaluate a potential delivery system. The group received support from the EPSRC, NERC and STFC to the tune of £2.1 million and was one of the first UK projects aimed at providing evidence-based knowledge about solar radiation management. Although the field testing was cancelled, the project panel decided to continue the lab-based elements of the project. Furthermore, a consultation exercise was undertaken with members of the public in a parallel project by Cardiff University, with specific exploration of attitudes to the SPICE test. This research found that almost all of the participants in the poll were willing to allow the field trial to proceed, but very few were comfortable with the actual use of stratospheric aerosols. A campaign opposing geoengineering led by the ETC Group drafted an open letter calling for the project to be suspended until international agreement is reached, specifically pointing to the upcoming convention of parties to the Convention on Biological Diversity in 2012.

Stardust Solutions was established in 2023-24 as a for-profit venture capital backed SAI venture.

Implementation and technical considerations

Materials

Pinatubo eruption cloud. This volcano released huge quantities of stratospheric sulfur aerosols and contributed greatly to understanding of the subject.

Various forms of sulfur were proposed as the injected substance, as this is in part how volcanic eruptions cool the planet. Precursor gases such as sulfur dioxide and hydrogen sulfide have been considered. According to estimates, "one kilogram of well placed sulfur in the stratosphere would roughly offset the warming effect of several hundred thousand kilograms of carbon dioxide." One study calculated the impact of injecting sulfate particles, or aerosols, every one to four years into the stratosphere in amounts equal to those lofted by the volcanic eruption of Mount Pinatubo in 1991, but did not address the many technical and political challenges involved in potential solar geoengineering efforts. Use of gaseous sulfuric acid appears to reduce the problem of aerosol growth. Materials such as photophoretic particles, metal oxides (as in Welsbach seeding, and titanium dioxide), and diamond are also under consideration.

Delivery

Various techniques have been proposed for delivering the aerosol or precursor gases. The required altitude to enter the stratosphere is the height of the tropopause, which varies from 11 kilometres (6.8 mi/36,000 ft) at the poles to 17 kilometers (11 mi/58,000 ft) at the equator.

refer to caption and image description
Proposed tethered balloon to inject aerosols into the stratosphere
  • Civilian aircraft including the Boeing 747-400 and Gulfstream G550/650, C-37A could be modified at relatively low cost to deliver sufficient amounts of required material according to one study, but a later metastudy suggests a new aircraft would be needed but easy to develop.
  • Military aircraft such as the F15-C variant of the F-15 Eagle have the necessary flight ceiling, but limited payload. Military tanker aircraft such as the KC-135 Stratotanker and KC-10 Extender also have the necessary ceiling at latitudes closer to the poles and have greater payload capacity.
  • Modified artillery might have the necessary capability, but requires a polluting and expensive propellant charge to loft the payload. Railgun artillery could be a non-polluting alternative.
  • High-altitude balloons can be used to lift precursor gases, in tanks, bladders or in the balloons' envelope.

Injection system

The latitude and distribution of injection locations has been discussed by various authors. While a near-equatorial injection regime will allow particles to enter the rising leg of the Brewer-Dobson circulation, several studies have concluded that a broader, and higher-latitude, injection regime will reduce injection mass flow rates and/or yield climatic benefits. Concentration of precursor injection in a single longitude appears to be beneficial, with condensation onto existing particles reduced, giving better control of the size distribution of aerosols resulting. The long residence time of carbon dioxide in the atmosphere may require a millennium-timescale commitment to aerosol injection if aggressive emissions abatement is not pursued simultaneously.

Welsbach seeding (metal oxide particles)

Welsbach seeding is a patented solar radiation modification method, involving seeding the stratosphere with small (10 to 100 micron) metal oxide particles (thorium dioxide, aluminium oxide). The purpose of the Welsbach seeding would be to "(reduce) atmospheric warming due to the greenhouse effect resulting from a greenhouse gases layer," by converting radiative energy at near-infrared wavelengths into radiation at far-infrared wavelengths, permitting some of the converted radiation to escape into space, thus cooling the atmosphere. The seeding as described would be performed by airplanes at altitudes between 7 and 13 kilometres.

The method was patented by Hughes Aircraft Company in 1991, US patent 5003186. Quote from the patent: "This invention relates to a method for the reduction of global warming resulting from the greenhouse effect, and in particular to a method which involves the seeding of the earth's stratosphere with Welsbach-like materials." This is not considered to be a viable option by current geoengineering experts.

Cost

A study in 2020 looked at the cost of SAI through to the year 2100. It found that relative to other climate interventions and solutions, SAI remains inexpensive. However, at about $18 billion per year per degree Celsius of warming avoided (in 2020 USD), a solar geoengineering program with substantial climate impact would lie well beyond the financial reach of individuals, small states, or other non-state potential rogue actors. The annual cost of delivering a sufficient amount of sulfur to counteract expected greenhouse warming is estimated at $5–10 billion US dollars.

SAI is expected to have low direct financial costs of implementation, relative to the expected costs of both unabated climate change and aggressive mitigation.

Early studies suggest that stratospheric aerosol injection might have a relatively low direct cost. One analysis estimated the annual cost of delivering 5 million tons of an albedo enhancing aerosol to an altitude of 20 to 30 km is at US$2 billion to 8 billion, an amount which they suggest would be sufficient to offset the expected warming during the next century. In comparison, the annual cost estimates for climate damage or emission mitigation range from US$200 billion to 2 trillion.

A 2016 study found the cost per 1 W/m2 of cooling to be between 5–50 billion USD/yr. Because larger particles are less efficient at cooling and drop out of the sky faster, the unit-cooling cost is expected to increase over time as increased dose leads to larger, but less efficient, particles by mechanism such as coalescence and Ostwald ripening. Assume RCP8.5, -5.5 W/m2 of cooling would be required by 2100 to maintain 2020 climate. At the dose level required to provide this cooling, the net efficiency per mass of injected aerosols would reduce to below 50% compared to low-level deployment (below 1W/m2). At a total dose of -5.5 W/m2, the cost would be between 55–550 billion USD/yr when efficiency reduction is also taken into account, bringing annual expenditure to levels comparable to other mitigation alternatives.

Advantages

This graph shows the baseline radiative forcing under three different Representative Concentration Pathway scenarios, and how it would be affected by the deployment of SAI, starting from 2034, to halve the speed of warming by 2100, to halt the warming, or to reverse it entirely.

The advantages of this approach in comparison to other solar geoengineering methods include:

  • Mimics a natural process: Stratospheric sulfur aerosols are created by existing natural processes (especially volcanoes), whose impacts have been studied via observations. This contrasts with other, more speculative solar geoengineering techniques which do not have natural analogs (e.g., space sunshade).
  • Technological feasibility: In contrast to other proposed solar geoengineering techniques, such as marine cloud brightening, much of the required technology is pre-existing: chemical manufacturing, artillery shells, high-altitude aircraft, weather balloons, etc. Unsolved technical challenges include methods to deliver the material in controlled diameter with good scattering properties.
  • Scalability: Some solar geoengineering techniques, such as cool roofs and ice protection, can only provide a limited intervention in the climate due to insufficient scale—one cannot reduce the temperature by more than a certain amount with each technique. Research has suggested that this technique may have a high radiative 'forcing potential', yet can be finely tuned according to how much cooling is needed.
  • Speed: A common argument is that stratospheric aerosol injection can take place quickly, and would be able to buy time for carbon sequestration projects such as carbon dioxide air capture to be implemented and start acting over decades and centuries.

Uncertainties

It is uncertain how effective any solar geoengineering technique would be, due to the difficulties modeling their impacts and the complex nature of the global climate system. Certain efficacy issues are specific to stratospheric aerosols.

  • Lifespan of aerosols: Tropospheric sulfur aerosols are short lived. Particles delivered into the lower stratosphere in the arctic will typically remain aloft only for a few weeks or months, as air in this region is predominantly descending. To ensure endurance, higher-altitude delivery is needed; particles injected into the rising leg of the Brewer-Dobson circulation above the tropical tropopause typically remain aloft for several years. Sizing of particles is also crucial to their endurance.
  • Aerosol delivery: There are two proposals for how to create a stratospheric sulfate aerosol cloud, either through the release of a precursor gas (SO
    2
    ) or the direct release of sulfuric acid (H
    2
    SO
    4
    ) and these face different challenges. If SO
    2
    gas is released it will oxidize to form H
    2
    SO
    4
    and then condense to form droplets far from the injection site. Releasing SO
    2
    would not allow control over the size of the particles that are formed but would not require a sophisticated release mechanism. Simulations suggest that as the SO
    2
    release rate is increased there would be diminishing returns on the cooling effect, as larger particles would be formed which have a shorter lifetime and are less effective scatterers of light. If H
    2
    SO
    4
    is released directly then the aerosol particles would form very quickly and in principle the particle size could be controlled although the engineering requirements for this are uncertain. Assuming a technology for direct H
    2
    SO
    4
    release could be conceived and developed, it would allow control over the particle size to possibly alleviate some of the inefficiencies associated with SO
    2
    release.
  • Strength of cooling: The magnitude of the effect of forcing from aerosols by decreasing insolation received at the surface is not completely certain, as its scientific modelling involves complex calculations due to different confounding factors and parameters such as optical properties, spatial and temporal distribution of emission or injection, albedo, geography, loading, rate of transport of sulfate, global burden, atmospheric chemistry, mixing and reactions with other compounds and aerosols, particle size, relative humidity, and clouds. Along with others, aerosol size distribution and hygroscopicity have particularly high uncertainty due to being closely related to sulfate aerosol interactions with other aerosols which affects the amount of radiation reflected. As of 2021, state-of-the-art CMIP6 models estimate that total cooling from the currently present aerosols is between 0.1 °C (0.18 °F) to 0.7 °C (1.3 °F); the IPCC Sixth Assessment Report uses the best estimate of 0.5 °C (0.90 °F), but there's still a lot of contradictory research on the impacts of aerosols of clouds which can alter this estimate of aerosol cooling, and consequently, our knowledge of how many millions of tons must be deployed annually to achieve the desired effect.
Anthropogenic sulfate aerosols have decreased precipitation over most of Asia (red), but increased it over some parts of Central Asia (blue).
  • Hydrological cycle: Since the historical global dimming from tropospheric sulfate pollution is already well-known to have reduced rainfall in certain areas, and is likely to have weakened Monsoon of South Asia and contributed to or even outright caused the 1984 Ethiopian famine, the impact on the hydrological cycle and patterns is one of the most-discussed uncertainties of the different stratospheric aerosol injection proposals. It has been suggested that while changes in precipitation from stratospheric aerosol injection are likely to be more manageable than the changes expected under future warming, one of the main impacts it would have on mortality is by shifting the habitat of mosquitoes and thus substantially affecting the distribution and spread of vector-borne diseases. Considering the already-extensive present-day mosquito habitat, it is currently unclear whether those changes are likely to be positive or negative.

Risks

Turner was inspired by dramatic sunsets caused by volcanic aerosols

Solar geoengineering in general poses various problems and risks. However, certain problems are specific to or more pronounced with stratospheric sulfide injection.

  • Ozone depletion: a potential side effect of sulfur aerosols; and these concerns have been supported by modelling. However, this may only occur if high enough quantities of aerosols drift to, or are deposited in, polar stratospheric clouds before the levels of CFCs and other ozone destroying gases fall naturally to safe levels because stratospheric aerosols, together with the ozone destroying gases, are responsible for ozone depletion. The injection of other aerosols that may be safer such as calcite has therefore been proposed. The injection of non-sulfide aerosols like calcite (limestone) would also have a cooling effect while counteracting ozone depletion and would be expected to reduce other side effects.
  • Whitening of the sky: Volcanic eruptions are known to affect the appearance of sunsets significantly, and a change in sky appearance after the eruption of Mount Tambora in 1816 "The Year Without A Summer" was the inspiration for the paintings of J. M. W. Turner. Since stratospheric aerosol injection would involve smaller quantities of aerosols, it is expected to cause a subtler change to sunsets and a slight hazing of blue skies. How stratospheric aerosol injection may affect clouds remains uncertain.
  • Stratospheric temperature change: Aerosols can also absorb some radiation from the Sun, the Earth, and the surrounding atmosphere. This changes the surrounding air temperature and could potentially impact the stratospheric circulation, which in turn may impact the surface circulation.
  • Deposition and acid rain: The surface deposition of sulfate injected into the stratosphere may also have an impact on ecosystems. However, the amount and wide dispersal of injected aerosols means that their impact on particulate concentrations and acidity of precipitation would be very small.
  • Ecological consequences: The consequences of stratospheric aerosol injection on ecological systems are unknown and potentially vary by ecosystem with differing impacts on marine versus terrestrial biomes.
  • Mixed effects on agriculture: A historical study in 2018 found that stratospheric sulfate aerosols injected by the volcanic eruptions of Chicón (1982) and Mount Pinatubo (1991) had mixed effects on global crop yields of certain major crops. Based on several studies, the IPCC Sixth Assessment Report suggests that crop yields and carbon sinks would be largely unaffected or may even increase slightly, because reduced photosynthesis due to lower sunlight would be offset by CO2 fertilization effect and the reduction in thermal stress, but there's less confidence about how the specific ecosystems may be affected.
  • Inhibition of Solar Energy Technologies: Uniformly reduced net shortwave radiation would hurt solar photovoltaics by the same 2–5% as for plants. The increased scattering of collimated incoming sunlight would more drastically reduce the efficiencies (by 11% for RCP8.5) of concentrating solar thermal power for both electricity production and chemical reactions, such as solar cement production.

Governance

Most of the existing governance of stratospheric sulfate aerosols is from that which is applicable to solar radiation management more broadly. However, some existing legal instruments would be relevant to stratospheric sulfate aerosols specifically. At the international level, the Convention on Long-Range Transboundary Air Pollution (CLRTAP Convention) obligates those countries which have ratified it to reduce their emissions of particular transboundary air pollutants. Notably, both solar radiation management and climate change (as well as greenhouse gases) could satisfy the definition of "air pollution" which the signatories commit to reduce, depending on their actual negative effects. Commitments to specific values of the pollutants, including sulfates, are made through protocols to the CLRTAP Convention. Full implementation or large scale climate response field tests of stratospheric sulfate aerosols could cause countries to exceed their limits. However, because stratospheric injections would be spread across the globe instead of concentrated in a few nearby countries, and could lead to net reductions in the "air pollution" which the CLRTAP Convention is to reduce so they may be allowed.

The stratospheric injection of sulfate aerosols would cause the Vienna Convention for the Protection of the Ozone Layer to be applicable due to their possible deleterious effects on stratospheric ozone. That treaty generally obligates its Parties to enact policies to control activities which "have or are likely to have adverse effects resulting from modification or likely modification of the ozone layer." The Montreal Protocol to the Vienna Convention prohibits the production of certain ozone depleting substances, via phase outs. Sulfates are presently not among the prohibited substances.

In the United States, the Clean Air Act might give the United States Environmental Protection Agency authority to regulate stratospheric sulfate aerosols.

Labor theory of value

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