Climatic Change

, Volume 130, Issue 2, pp 299–312 | Cite as

Exploring public perceptions of stratospheric sulfate injection

  • Christine Merk
  • Gert Pönitzsch
  • Carola Kniebes
  • Katrin Rehdanz
  • Ulrich Schmidt


Injecting sulfate aerosols into the stratosphere could quickly offset global warming caused by anthropogenic greenhouse gas emissions. Because the technology would have global side effects, it raises not only technological but also political, ethical, and social concerns. Therefore, research on sulfate injection should be accompanied by a global debate that incorporates public perceptions and concerns into the development and governance of the technology. Our paper provides insight into public perceptions and explores their underlying patterns using a survey conducted in Germany. The data reveal a differentiated picture. Laboratory research on sulfate injection is broadly approved, whereas field research is much less approved. Immediate deployment is largely rejected. The acceptance of the technology is associated with the belief that climate change is a serious problem and that humans will eventually be able to control nature. It is also determined by the levels of trust in scientists and firms. Among the strongest objections against the technology is the belief that humans should not manipulate nature in the way injecting sulfate would. The actual public perceptions of sulfate injection will, however, evolve along with the ongoing debate between the public, experts, and policymakers.

1 Introduction

New technological options to reduce global warming are currently under discussion because international efforts to mitigate climate change continue to progress slowly. These options, known as climate engineering (CE) or geoengineering, involve deliberate large-scale interventions in the climate system to reduce global warming. They increasingly appear in mass media, enter political discussions (Mercer et al. 2011), and were recently mentioned in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report (IPCC 2013).

CE encompasses two approaches. The first approach, carbon dioxide removal (CDR), is to reduce atmospheric concentrations of carbon dioxide. The second approach, solar radiation management (SRM), is to increase the Earth’s albedo to reflect more sunlight back into space. Our paper addresses the most prominent and controversial method of SRM, which is the injection of sulfate aerosols into the stratosphere. In contrast to other methods to counteract climate change, sulfate injection can be deployed quickly and causes direct reductions in global temperature (Robock et al. 2008). In addition, it has been suggested that it involves low operational costs (Barrett 2008). Such claims, however, ignore additional economic costs like price and external effects (Rickels and Klepper 2012). Especially external effects could result in very high total costs because the risks of sulfate injection are substantial and global (Royal Society 2009).

A comprehensive discussion is needed to support informed decisions on research and deployment of sulfate injection because the technology involves a deliberate manipulation of the Earth’s environmental system, there are major uncertainties regarding its side effects, and the consequences of its use are global. The assessment of sulfate injection thus must address legal, political, ethical, and social issues (see Royal Society 2009 and Rickels et al. 2011 for an overview). While expert assessments are necessary to inform the debate, the issues ultimately raise value-based questions that the public might evaluate differently than experts (Pidgeon et al. 2013). Research on public perceptions can provide initial insights into public concerns and thereby inform decisions on future research and on the potential development of the technology. Its aim is not to influence public opinion in any particular direction or to replace legitimate democratic political decision-making but to better understand the public’s sensitivities and its criteria for assessing the technology (Corner et al. 2012; Carr et al. 2013).

Based on a large-scale survey conducted in Germany, we contribute to the discussion on stratospheric sulfate injection by answering two important questions: (1) how does the public perceive different types of research and deployment of sulfate injection in different circumstances? and (2) what factors drive public perceptions of sulfate injection?

Our first research question extends recent results on public perceptions of CE options: it includes the perceptions of different types of research on sulfate injection and it confirms previous findings on the perceptions of aerosol injection for a country in which public perceptions of sulfate injection have not previously been studied. Many earlier studies have investigated CE options in general and did not distinguish between different types of research or different circumstances of deployment. These studies also varied considerably in the level of detail they provided in describing the technology. Most referred only briefly to CE technologies as a climate change policy option (Borick and Rabe 2012; Bostrom et al. 2012; Leiserowitz et al. 2012; Spence et al. 2010), while others provided more information on SRM as well as CDR technologies (Kahan et al. 2012; US GAO 2011). These studies were primarily conducted in the US and the UK. To date, two surveys have investigated public perceptions of aerosol injection and included a section with information on the technology. Mercer et al. (2011) surveyed respondents in Canada, the UK, and the US; Sugiyama and Fujiwara (2012) surveyed respondents in Japan. They assessed the perceptions of general research, immediate deployment of the technology, emergency deployment, and complete rejection of the use of the technology.

Public awareness of CE in general and of specific CE technologies remains low. The share of people who have never previously heard about climate engineering or geoengineering ranges from 65 % (US GAO 2011), to 75 % (Buck 2010; Spence et al. 2010; Mercer et al. 2011; Pidgeon et al. 20121), and 90 % (Sugiyama and Fujiwara 2012). Overall, research on public perceptions finds a low level of support for these technologies (Bellamy and Hulme 2011; Borick and Rabe 2012; Bostrom et al. 2012; Macnaghten and Szerszynski 2013) and a preference for mitigation over CE as policy option against climate change (Pidgeon et al. 2012; US GAO 2011). Accordingly, survey respondents tend to agree that employing aerosol injection to counteract climate change would be the easy way out (Mercer et al. 2011; Sugiyama and Fujiwara 2012), and workshop participants tend to be concerned about the inability of aerosol injection to address increasing greenhouse gas emissions (Pidgeon et al. 2013).

Previous research indicates that public perceptions vary depending on the specific context. First, opinions toward deployment depend on the circumstance in which the technology would be deployed. Mercer et al. (2011) and Sugiyama and Fujiwara (2012) report higher acceptance of deployment of aerosol injection in the case of a climate emergency compared to the case in which the technology would be deployed as soon as it were technically feasible. Second, public support for research does not necessarily entail support for actual use of the technology. Pidgeon et al. (2013) note that participants in deliberative workshops often express negative views of stratospheric aerosol injection in general but express more nuanced views of the UK research project SPICE (Stratospheric Particle Injection for Climate Engineering), which was supposed to involve field tests.2 Also, surveys report that research on aerosol injection is more acceptable than actual deployment (Mercer et al. 2011; Sugiyama and Fujiwara 2012).

Public perceptions are also likely to vary between the different types of research on sulfate injection. Research activities might be classified into laboratory research that involves the use of computer models and laboratory experiments and field research that involves the release of materials into the environment (SRMGI 2011). Different types of research involve different levels of interference with nature and potentially involve different perceived direct risks (e.g., threats to the environment) and perceived indirect risks (e.g., creating a slippery slope toward deployment). To address this issue, the present study distinguishes not only between different circumstances of deployment but also between different types of research.

Our second research question examines the factors that influence public acceptance, such as the perceived seriousness of climate change, risk aversion, attitudes toward sulfate injection, ecological attitudes, trust in institutions, religiosity, and socio-demographic variables. Previous studies have already investigated the importance of some of these factors. The perceived seriousness of climate change increases acceptance of sulfate injection as a potential solution to the problem (Mercer et al. 2011; Pidgeon et al. 2012; Sugiyama and Fujiwara 2012); although, the risks of massive climate change have to be weighed against the risks of sulfate injection. Thus, individuals’ level of risk aversion might be a potentially contributing factor, but its influence has yet to be researched. It might increase or decrease acceptance of sulfate injection, depending on the extent to which individuals attribute a higher risk to massive climate change or to sulfate injection. Our survey also includes items to examine two previously suggested arguments against the technology: that humans should not manipulate nature in this way and that using sulfate injection to combat climate change would be the too easy way out (Mercer et al. 2011). These attitudes might also be related to beliefs about human technological ingenuity (Kahan et al. 2012) and the relationship between humans and nature (Corner et al. 2013). Thus, the survey includes items about these two aspects, which we collectively refer to as ecological attitudes. We expect that individuals with the belief that humans were meant to rule the Earth or that humans would eventually learn enough to control the environment would be more willing to accept sulfate injection, while individuals expressing concerns about the fragility of the balance of nature might either reject or accept the technology, depending on whether it was viewed as disrupting or restoring nature (Corner et al. 2013). Another potential objection to the use of the technology is the perception that humans might be ‘playing God’ (Carr 2014); the survey, thus, includes religiosity to account for the role of religious beliefs.

Another relevant factor for the public perceptions of research and deployment is the governance framework and the extent to which people trust that different policy and decision makers will act responsibly. Findings from focus groups on solar radiation management indicate that confidence in the ability of research to forecast risks and benefits as well as confidence in effective and democratic governance are prerequisites for acceptance (Macnaghten and Szerszynski 2013). These results are consistent with prior findings on the positive effect of trust in institutions on the acceptance of large-scale risks (Earle 2010). Our study therefore examines the role of trust in different actors. Socio-demographic variables might also contribute to people’s perceptions; for example, Pidgeon et al. (2012) report lower levels of support for climate engineering in general among women and individuals with a lower level of education. Our analysis therefore accounts for socio-demographic variables.

By addressing these two research questions, the study broadens and deepens the understanding of public perceptions of sulfate injection and contributes to the previous literature in a number of ways. First, our survey is the first to explicitly distinguish between perceptions of laboratory and field research. Second, our survey is the first to study perceptions of sulfate injection in a continental European country (Germany). Compared to other Europeans, Germans express more negative attitudes toward nuclear energy and carbon capture and storage but more positive attitudes toward wind and hydroelectric energy (European Commission 2011). Our survey provides insights into Germans’ attitudes toward sulfate injection. Third, our survey investigates a wide range of factors that might influence public perceptions of sulfate injection. Finally, our study extends the descriptive analyses employed in previous studies (Mercer et al. 2011; Sugiyama and Fujiwara 2012) by employing a multiple regression framework to analyze the effect of these factors on public acceptance in different circumstances.

2 Survey design

We conducted an online survey to assess the perceptions of sulfate injection among the German population in December 2012. Survey respondents were recruited from an online panel and were sampled using quotas for the characteristics gender, age, and state of residence. The sample consisted of 1,040 respondents; half of the respondents were female. Respondents ranged in age from 18 to 81 years, with an average age of 47 years. Half of the respondents had a higher education entrance certificate, while the other half of the respondents had completed only lower secondary education or had no degree. As a result, respondents with a high level of education are overrepresented in the sample.

All items used in the analysis are presented in Table A-1 of the online appendix; responses to items were all assessed using Likert scales. The questionnaire consisted of three parts.

The first part contained questions assessing respondents’ attitude toward risk, the perception of the seriousness of climate change, and ecological attitudes. The attitude toward risk was assessed on the scale from Dohmen et al. (2011) ranging from 0 (′risk averse′) to 10 (′fully prepared to take risks′). In the analysis, the values were reversed to capture risk aversion. We also assessed the perception of the seriousness of climate change (Q3). Respondents’ ecological attitudes were measured using 5 of the 15 items of the New Ecological Paradigm Scale (NEP, Dunlap et al. 2000). They assess attitudes toward limits to growth (Q4-1), anthropocentrism (Q4-2), the fragility of the balance of nature (Q4-3), human exemptionalism (Q4-4), and the possibility of an imminent eco-crisis (Q4-5). Both the seriousness of climate change and the NEP were measured using a four-point scale that ranged from 1 (′strongly disagree′) to 4 (′strongly agree′).

The second part contained a video explaining anthropogenic climate change and sulfate injection followed by questions about the respondents’ perceptions. The video consisted of animated infographics and brief bullet points that were explained by an accompanying voice-over.3 First, respondents received information on the causes and likely consequences of climate change. Mitigation, adaptation, and sulfate injection were introduced as three options to address climate change.4 The video stated that sulfate injection would not prevent all consequences of climate change and that it was not a complete substitute for mitigation. The video then presented the risks and benefits of sulfate injection in greater detail. Because the goal was to present currently available information on the topic in a clear, scientifically accurate and unbiased manner, the information presented was based on peer-reviewed papers and scientific reports (e.g., Crutzen 2006; IPCC 2007; IPCC 2012; Rickels et al. 2011; Robock 2008); it reflects the broad consensus on climate change and the risks and benefits of sulfate injection at the time. Information on the technology was based in part on previous work (Mercer et al. 2011). Independent experts reviewed the information presented for clarity and accuracy.

Before the video, participants’ level of awareness of the technology was assessed (Q5). After the video, one item assessed the acceptance of laboratory research (Q10-1) and another item assessed the acceptance of field experiments (Q10-2). Following Mercer et al. (2011) and Sugiyama and Fujiwara (2012), respondents were asked about their acceptance of deployment in different circumstances: to avert massive and irreversible changes in the climate system due to climate change, i.e., in case of a climate emergency (Q10-3); as soon as the deployment of the technology was technically feasible, which we refer to as ′immediate deployment′ (Q10-5); or never, under no circumstances (Q10-4). The response scale for all these items (Q10) ranged from 1 (′strongly disagree′) to 4 (′strongly agree′). All these scenarios imply a continuation of mitigation efforts. The perception of overall benefit (Q11) and overall risk (Q12) was measured on a scale ranging from 1 (′very small′) to 4 (′very large′). The specific risks (Q13) and benefits (Q14) appeared in the questionnaire with the same wording which was used in the video; respondents’ perceptions were measured on a scale ranging from 1 (′negligible′) to 4 (′very serious′) (Q13) and from 1 (′very small′) to 4 (′very large′) (Q14), respectively. We also measured the extent to which respondents agreed with four items expressing different attitudes toward the injection of sulfate. For example, the statement ′Humans should not be manipulating nature in this way′ (Q17-3) was assessed on a scale ranging from 1 (′strongly disagree′) to 4 (′strongly agree′). Trust that different institutions or actors would act in the interest of society and the environment was measured on a scale ranging from 1 (′do not trust at all′) to 4 (′trust completely′).

The third part contained questions on respondents’ socio-demographic characteristics that were not available from the panel’s database. We have information on respondents’ gender, age, and state of residence as well as other characteristics, such as the level of education5 or whether the respondent had children. In addition, we assessed respondents’ religiosity (Q26) on a scale ranging from 1 (′not religious at all′) to 4 (′very religious′). At the end of the questionnaire, respondents had the opportunity to make comments on sulfate injection (Q36). 78 % of the respondents made 1,436 different statements in total. The statements were coded by a research assistant who was otherwise not involved in the research.

3 Descriptive results

In the following, we describe responses to the questionnaire. When appropriate, we aggregate responses from the four-point Likert scales into two categories. For example, we speak of agreement when respondents choose the categories ′strongly agree′ or ′somewhat agree′. Correspondingly, we speak of disagreement when respondents choose the categories ′strongly disagree′ or ′somewhat disagree′.

3.1 Public awareness and perceptions of the video

Currently, the German population does not exhibit widespread awareness of sulfate injection. Before watching the video, 80 % of the respondents state that they have not previously heard about spraying sulfate particles into the atmosphere at a high altitude to counteract climate change; 17 % recognize the technology and state that they had heard a little about it; and 3 % state that they had heard a lot about it (Q5). After watching the video, 80 % state that they perceived the video’s position toward sulfate injection as neutral; 13 % state that the video was biased in favor of the technology; and 1 % stated that the video was biased against it (Q9). Only ten of the 1,040 respondents report difficulties in understanding the video (Q8).6

3.2 Acceptance

Figure 1 summarizes the findings regarding acceptance of the different types of research and acceptance of deployment in different circumstances. Laboratory research is widely accepted; with 80 % of respondents agreeing that scientists should study sulfate injection through computer models and laboratory experiments (Q10-1). Acceptance of field research involving small-scale experiments in the atmosphere is markedly different; only 47 % of the respondents are in favor of field research (Q10-2). This implies that approximately one-third of the respondents believe that research should be conducted in the laboratory but not in the field.
Fig. 1

Acceptance of different types of research and of deployment in different circumstances

The most accepted circumstance for deployment is in case of a climate emergency. Slightly more than half of the respondents (56 %) agree with deployment in this case (Q10-3). The relatively high acceptance of emergency deployment indicates that some respondents support emergency deployment despite their opposition to field research. The most immediate form of deployment is as soon as it is technically feasible (Q10-5). 22 % of the respondents support immediate deployment, while 70 % of the respondents disagree – many of them indicating strong disagreement. 35 % of the respondents agree that sulfate injection should never be used regardless of the situation (Q10-4), with 18 % of all respondents strongly agreeing that the technology should never be used. In summary, the respondents’ opinions regarding sulfate injection vary across types of research and circumstances of deployment.

3.3 Attitudes toward sulfate injection

We explore key attitudes toward sulfate injection using further questions. More than 70 % of the respondents think both that humans should not be manipulating nature in this way (Q17-3) and that using the technology to counteract climate change would mean to take the too easy way out (Q17-1).7 Both attitudes also feature prominently in the free-form comments made at the end of the survey. Many respondents voice concerns that humans should respect nature and ′not play God′. Others state that the causes rather than the symptoms of climate change should be addressed.

A strong concern in the discussion about the technology is about the final decision regarding implementation. Specifically, research on sulfate injection might create a slippery slope toward its implementation. Respondents express the belief that research into the technology would lead to its deployment no matter what the public thinks (Q17-2); 71 % of the respondents agree with this statement. The strong concern about the deployment decision is also visible in the free-form comments. The comments express the need to involve all nations as well as the general public in the decision-making process.

3.4 Perceptions of risks and benefits

We asked respondents to judge the extent of the overall risk of sulfate injection and the severity of its specific risks. The overall risk (Q12) is perceived as large; 81 % of the respondents view the risk as very large or somewhat large, and 42 % view the risk as very large.

Respondents exhibit the most concern about the abrupt temperature change that would be caused by a sudden termination of sulfate injection (Q13-4) and the risk of yet unknown and unpredictable consequences (Q13-3). For both these risks, at least 88 % of the respondents perceive them as serious. 85 % of the respondents perceive changes in precipitation as a serious risk (Q13-1). Respondents exhibit only slightly less concern about the persistence of carbon-intensive lifestyles if sulfate injection were deployed (Q13-2). Finally, international conflicts caused by trans-boundary side effects (Q13-5) are perceived as a serious risk by 72 % of the respondents.

The perception that the risks are serious is dominant; any specific risk is viewed as serious by more than 72 % of the respondents. Moreover, apart from the risk of international conflict, 45 % of the respondents view each specific risk as very serious. Concerns about specific risks are also frequently mentioned in the free-form comments.

Similarly, we asked respondents to judge the extent of the overall benefit and specific benefits of sulfate injection. In contrast to the perceptions of risks, the perceptions of benefits show a higher variance across respondents. The overall benefit (Q11) is perceived to be small by 51 % of the respondents, and perceived to be large by 41 % of the respondents. Only few responses fall into the categories ′very large′ (6 %) or ′very small′ (12 %); respondents do not display extremely positive or negative opinions regarding the overall benefit of sulfate injection.

The evaluation of specific benefits yields a differentiated picture. The possibility of preventing massive, irreversible changes in the climate (Q14-2) is most often perceived as a large benefit of the technology; 54 % of respondents perceive this benefit as large. The speed at which the climate can be cooled (Q14-1) comes second; 51 % perceive this benefit as large. The possibility of unilaterally deploying sulfate injection (Q14-4) and the comparatively low costs of implementation (Q14-3) are less often rated as beneficial; 42 and 35 % of the respondents perceive these benefits as large, respectively.

4 Regression analysis

To further analyze public acceptance of sulfate injection and its underlying patterns, we conducted a regression analysis.

As predictors of acceptance, we used the variables that were discussed in Section 1 and described in Section 2. The econometric model thus includes independent variables capturing risk aversion, perceived seriousness of climate change, ecological attitudes, trust in different institutions, attitudes toward sulfate injection, religiosity, and socio-demographic factors.8 We did not include the awareness of sulfate injection because the variable shows too little variation. The dependent variables capture acceptance in different circumstances and take ordered values ranging from 1 (′strongly disagree′) to 4 (′strongly agree′). We, hence, used ordered logistic regression as the estimation procedure.

Table 1 presents the regression results. The columns display regression results for (1) laboratory research, (2) field research, (3) deployment in case of a climate emergency, and (4) immediate deployment.
Table 1

Results obtained from ordered logistic regressions

















Risk aversion






Seriousness of climate change





Ecological attitudes


Limits to growth












Balance of nature






Human exemptionalism






Risk of an eco-crisis







Is too easy way out






Not manipulate this way













Firms involved






Environmental org.


















United Nations






European Union



















High education
























Pseudo R2





***, **, * indicate significance at the 1-, 5-, and 10-percent level, respectively. Scales are from 1 to 4. Exceptions are dummy variables (female, high education, and children), risk attitude (scale is from 0 to 10), and age. Variables indicated by (DB) are part of the panel’s database

Most of the explanatory variables have a significant effect on acceptance. Risk aversion (Q2) negatively affects the acceptance of field research and immediate deployment. The perceived seriousness of climate change (Q3) increases the acceptance of field research and of deployment in case of a climate emergency. In contrast, the perceived seriousness of climate change does not increase the acceptance of immediate deployment. This finding is in line with the consequences of climate change primarily occurring in the future and the belief that serious consequences might still be averted by other means.

With respect to ecological attitudes, the belief in human exemptionalism (Q4-5), i.e., humans’ ability to control the environment, displays the strongest predictive power. It has a strong positive effect on people’s acceptance of field research and deployment. The risk of an eco-crisis (Q4-6) predicts acceptance of immediate deployment. Because the item reflects beliefs about the imminence of a crisis, it captures the perceived need for timely action. The belief that the balance of nature is fragile and easily upset (Q4-4) increases acceptance of laboratory research, but it does not affect acceptance of implementation. Anthropocentrism (Q4-3), i.e., the belief in humans’ designation to rule over nature, and the belief in limits to growth (Q4-2) only have a minor impact on acceptance. Religiosity (Q26) does not have additional explanatory power on top of the other attitudinal items in the model.

Apart from general attitudes toward the environment and the human-environment interaction, the belief that humans should not manipulate nature in this way (Q17-3) strongly decreases acceptance of research and deployment. It also decreases acceptance of the technology as a way to counteract a climate emergency. The attitude that injecting sulfate would be the too easy way out (Q17-1) decreases the acceptance of immediate deployment. This result is consistent with the notion that deployment should only be considered when every other option has been exhausted.

Trust that different institutions or actors would act in the interest of society and the environment significantly affects acceptance. The most important determinant from this group of variables is trust in scientists (Q23-5) who perform research on sulfate injection. Another important determinant is trust in firms (Q23-2) involved in sulfate injection projects. Trust in firms is a prerequisite for the acceptance of field research and immediate deployment. For the acceptance of laboratory research, however, in which firms’ involvement is likely to be low, trust in firms is not a significant predictor. Trust in firms is also not a significant predictor for the acceptance of deployment in case of a climate emergency. In this circumstance, typical problems with respect to firms, such as vested interests, might be expected to play a minor role. Trust in government (Q23-1) is another predictor of acceptance, although it is not as important as trust in scientists or firms. First, trust in the federal government is positively associated with the acceptance of field research. This relationship might reflect trust in the rules for research set by the government. Second, trust in the EU is positively associated with the acceptance of immediate deployment. Trust in environmental organizations (Q23-3) is only modestly associated with acceptance after controlling for ecological attitudes. Trust in environmental organizations is positively associated with the acceptance of laboratory research, which may reflect a lower perceived risk of hasty deployment. Trust in the media (Q23-4) does not predict acceptance.

In addition, the socio-demographic variables education and age exhibit explanatory power. A high level of education (Q34) reduces the acceptance of field research and deployment. This finding might reflect differences in information processing, in dealing with complexity, or in socio-economic status. The level of education most strongly affects the acceptance of immediate deployment. The effect of age depends on the circumstance of deployment. Age is positively related to the acceptance of immediate deployment but negatively related to the acceptance of emergency deployment. These relationships are not consistent with an inter-temporal risk-risk tradeoff and thus point to particular intergenerational differences in the perceptions of sulfate injection. Neither gender nor having children (Q32) are related to acceptance of the technology.

Our results proved to be robust to alternative specifications. First, we checked whether it is appropriate to include the independent variables as continuous variables by running regressions using binary indicators for the levels of these variables. The results confirm that the effects of the independent variables are linear.9 Second, we checked for differences in acceptance across German states to control for interregional differences in factors, such as religious composition or population density. The results are not significantly different. Finally, we ran regressions using binary and multinomial logistic models. The direction and the significance of the coefficients remain similar.

5 Discussion and conclusion

Overall, German respondents are highly skeptical of sulfate injection. The views depend on the type of research and the circumstance of deployment. First, respondents’ higher acceptance of laboratory research compared to field research reveals their concern regarding the negative side effects of field research. The finding highlights the importance of (1) identifying what can be learned without actually intervening in the Earth’s environmental system (Robock et al. 2013), (2) identifying the type of research to be performed when communicating with the public and (3) establishing a governance framework for research (SRMGI 2011). Second, the higher level of acceptance of emergency deployment compared to immediate deployment reflects respondents’ belief that climate change might still be averted by other means. Finally, the higher level of acceptance of laboratory research compared to any type of deployment suggests that respondents perceive laboratory research as a means to better understand the technology’s side effects or as a way to develop an insurance against massive and irreversible climate change.

The distinction between different circumstances and their implications is also relevant when examining the factors influencing acceptance of the technology. The perceived seriousness of climate change is positively associated with acceptance of research and emergency deployment. Faced with the risk-risk trade-off between climate change and sulfate injection, respondents who are more concerned about climate change seem not to want to dismiss the technology out of hand. Additionally, the perception that sulfate injection would be taking the too easy way out, i.e., shirking the responsibility for climate change, decreases the acceptance of immediate deployment but does not reduce the acceptance of research. This suggests that spending money on researching sulfate injection rather than mitigation is not currently viewed as problematic.

We also examine beliefs about the relationship between humans and nature as potential determinants of acceptance. The perceived fragility of the balance of nature, however, is neither positively not negatively associated with the acceptance of the deployment of sulfate injection, which reflects the unresolved debate on whether the technology is beneficial or detrimental to nature (Corner et al. 2013; Rickels et al. 2011). However, the positive association of this belief with the acceptance of laboratory research again reveals the perceived value of sulfate injection as a way to insure against climate change. In contrast, the belief about human interaction with nature strongly influences acceptance. Respondents who believe that humans will eventually be able to control the environment are more accepting of the technology, which might reflect a trust in technology and humans’ ability to devise a technological solution to the problem.

The belief that humans should not manipulate nature in this way exhibits the strongest downward impact on acceptance for all types of research and circumstances of deployment. This belief might be interpreted in various ways. It is not associated with religious concerns (Spearman’s ρ = -.02; p = .6) but it is positively correlated with risk aversion (Q2; ρ = .11; p < .01) and negatively correlated with the beliefs that humans should govern nature (Q4-3; ρ = -.22; p < .001) and that humans were able to control nature (Q4-4; ρ = -.23; p < .001). It is also strongly correlated with the belief that climate change should be dealt with differently (Q17-1; ρ = 0.50, p < .001). Because these factors were controlled for in the regression analysis, the belief that humans should not manipulate nature in this way is likely to represent further aspects that influence acceptance, such as the novelty or the perceived naturalness of the technology. Once people become familiar with the concept of sulfate injection, they might perceive the technology differently. In particular, this change in familiarity might be accompanied by a change in the public’s conceptualization of nature and the human-environment interaction (Hansen 2006). The dynamics of people’s attitudes toward sulfate injection provide an interesting avenue for future research.

Among the socio-demographic variables, both the level of education and age are significantly associated with acceptance. The specific mechanisms underlying these relationships merit further research as well.

As expected, trust in relevant actors is an important determinant of acceptance. Trust in scientists is the most important prerequisite. This is consistent with the high level of uncertainty regarding the risks of sulfate injection. Trust in firms is important with respect to field research and immediate deployment because the vested interests of firms and a lack of public involvement might create a slippery slope in which research leads to deployment of the technology. These findings indicate that transparency in research and technology use must be a key component of any governance framework and thus highlight one of the Oxford Principles (Rayner et al. 2009).

Overall, our results indicate that sulfate injection is primarily acceptable when it is viewed as an insurance against massive climate change, i.e., a risk management tool. This is consistent with previous research findings that mitigation is preferred to aerosol injection (Pidgeon et al. 2012; US GAO 2011). At the same time, our results reveal that the technology cannot be easily dismissed on the grounds of public acceptance. They highlight the need for appropriate decision-making structures to ensure democratic legitimacy (Victor 2008; Virgoe 2009), to improve decision making, to establish trust, and to respect ethical standards (Carr et al. 2013).

We examine public concerns in Germany, a country in which public perceptions of sulfate injection have not previously been studied. Compared to the results of similar surveys in other countries (Mercer et al. 2011; Sugiyama and Fujiwara 2012), our findings exhibit either a similar pattern of responses or somewhat more critical responses. Our respondents are more likely to perceive sulfate injection as the too easy way out and less likely to accept immediate deployment of the technology. However, the comparability of the studies is limited due to differences in the information presented, the wording of the questions, and the questionnaire design. To ensure a broad and comprehensive dialogue regarding sulfate injection, it is critical to identify public perceptions and concerns for a wide range of countries and cultures. Future surveys should allow for direct comparison of results from a representative set of countries that includes developing countries and the countries that are most vulnerable to the effects of climate change. In addition, our survey investigates several factors influencing public perceptions. These factors might be expected to vary for different countries, such as the level of trust in institutions (WVS 2013) and concern for the environment (Marquart-Pyatt 2012). Conflict lines are thus likely to occur at both the national and international level.

As other survey results, our findings must be interpreted cautiously. Corner et al. (2012: 454) note that respondents’ lack of prior knowledge of the topic creates the risk that “…participants have been told what they are responding to rather than deciding for themselves how to interpret the item.” We, therefore, paid specific attention to ask balanced questions without leading cues. In addition, the ′don’t know′ option was included in every item to signal that not answering was acceptable. The sequence of items within the questions was randomized, and we arranged the questions in a way that prevents or minimizes bias due to order effects. We also consulted with experts on survey design to ensure that our questionnaire met current quality standards. We paid specific attention to frame the video in a balanced and neutral way. It must be noted, however, that the way in which information is framed might influence responses (Corner and Pidgeon 2014). Our results thus provide a snapshot of public perceptions obtained in a highly controlled setting in which the video was the main reference point for respondents’ perceptions. Although our sample is broadly representative of the German population, our respondents’ views may not reflect actual public perceptions once the technology is more widely known and different framings enter the public discourse.

Despite these limitations, our survey makes a valuable contribution to the emerging public debate on sulfate injection. With regard to future research, our results provide a useful reference point because our respondents’ perceptions were not influenced by previous public discourse or extensive media coverage but by a well-documented video. Our results provide information about public concerns that should prove useful for experts and policymakers and that could be incorporated into the formal assessment of the technology and the development of a governance framework. To avoid a slippery slope toward premature deployment, it is imperative that public concerns about sulfate injection are explored at an early stage (Carr et al. 2013; Corner et al. 2012) because the public can identify and discuss critical aspects of a technology even when relatively little information on the topic is available (Corner et al. 2012; Macnaghten and Szerszynski 2013). Our results thus provide a first glimpse of public concerns and opinions regarding stratospheric sulfate injection that is relevant for public opinion researchers, experts, and policymakers.


  1. 1.

    Pidgeon et al. 2012 and Spence et al. 2010 analyze the same dataset.

  2. 2.
  3. 3.

    The German video together with the accompanying transcript in English is provided in the online appendix.

  4. 4.

    The video initially described sulfate injection as ′spraying sulfate particles into the atmosphere at high altitude′ to reflect sunlight. When subsequently referring to the technology, both the video and the survey used the term ′solar radiation management′ or the abbreviation ′SRM′.

  5. 5.

    Respondents with a higher education entrance certificate were coded as having a high level of education in the analysis.

  6. 6.

    Respondents were not able to skip or fast forward the video.

  7. 7.

    The connotation of the German expression for taking the too easy way out is that sulfate injection cannot be right; taking the too easy way out is considered to shirk one′s responsibility or to be thoughtless.

  8. 8.

    Summary statistics are available in table A-2 in the online appendix.

  9. 9.

    Results of this robustness check are presented in table A-3 in the online appendix.



This paper is part of the project ACCEPT which is funded by the German Federal Ministry for Education and Research (grant number 01LA1112A). We would like to thank three anonymous reviewers, Ashley Mercer, Nick Pidgeon, Andreas Oschlies, Gernot Klepper, Wilfried Rickels, Dorothee Amelung, and Timo Goeschl for their helpful comments and suggestions. We also thank participants of an IASS seminar, the Oxford Summer School on Geoengineering Research, and research seminars in Kiel. Furthermore, we want to thank Swantje Sundt for valuable research assistance.

Supplementary material

10584_2014_1317_MOESM1_ESM.pdf (180 kb)
ESM 1(PDF 179 kb)

Slide 1 Sunlight warms the Earth and the Earth’s atmosphere. Greenhouse gases in the atmosphere, such as CO2, ensure that a certain amount of heat remains close to the Earth’s surface. This makes the Earth warm enough for humans, animals, and plants to survive.

Slide 2 Since the beginning of industrialization around the year 1850, humans have emitted large amounts of greenhouse gases, for example, by burning coal, oil, and gas. These gases trap additional heat in the atmosphere and cause a gradual increase in the average global temperature.

Slide 3 – 8 Since 1900, the global temperature has risen on average by approximately 0.8°C. Almost all countries agree that the increase in the average global temperature should not exceed 2°C compared to the temperature at the beginning of the industrialization. This is referred to as the 2°C goal. A future temperature increase between 0.9°C and 5.4°C is expected by 2100. The outcome depends especially on the amount of greenhouse gases emitted in the future. To reach the 2°C goal, the current level of emissions would have to decrease by more than half by 2050. By 2100, almost no greenhouse gases should be emitted.

Slide 9 Climate change will almost certainly cause a rise in sea levels. It is very likely that both the frequency of heat waves and the number of heavy precipitation events will increase in many regions. In the future, it is likely that more areas will be affected by longer droughts and that the frequency and the intensity of tropical cyclones will increase. In addition, because oceans absorb some of the CO2 in the atmosphere, they will become more acidic.

Slide 10 There are different ways to deal with climate change: We can reduce greenhouse gas emissions or adapt to the new climate – for example, by building dikes or using more robust plants in agriculture. Another option is to reduce the global temperature by deploying solar radiation management (SRM).

Slide 11 Through SRM, a portion of the sunlight is reflected before it can warm the Earth. This can be achieved by, for example, spraying sulfate particles into the atmosphere at a high altitude. A similar phenomenon is observed in nature. When large volcanoes erupt, similar particles are distributed across wide areas of the Earth’s atmosphere, which cools the Earth.

Slide 12 The particles remain in the higher regions of the atmosphere for about two years. To prevent the Earth from heating up again, spraying would have to be continued until the cause of global warming is removed. Because the emitted CO2 stays in the atmosphere for a very long time, SRM might have to be used for several centuries. Ocean acidification will not be halted by using SRM. However, the 2°C goal could be met regardless of future greenhouse gas emissions by deploying SRM. Currently, researchers are investigating the risks, benefits, and feasibility of SRM.

Slide 13 The use of SRM entails benefits as well as risks. One benefit is that global warming might be slowed more quickly compared to cutting greenhouse gas emissions. This would provide mankind with additional time to remove the cause of climate change, i.e., the high concentration of greenhouse gases in the atmosphere. Massive and irreversible changes in the climate could be stopped before too much damage is done. Furthermore, it would be possible to stop climate change even if certain countries refused to reduce their greenhouse gas emissions. Deploying SRM would be cheaper than reducing the consumption of fossil fuels.

Slide 14 The risks include a change in the amount of precipitation in most regions. In particular, arid regions would have to cope with even less rain. If the deployment of SRM were suddenly halted, the global temperature would rise abruptly. The speed of this temperature rise might lead to severe problems for humans and the environment. Because possible side effects would occur across international boundaries, the use of SRM might cause international conflicts. Once used, SRM might take away people’s motivation to change their lifestyle and the emission of greenhouse gases would continue to increase. Furthermore, there would be the threat of other unknown and unforeseeable risks.

10584_2014_1317_MOESM3_ESM.pdf (947 kb)
ESM 3(PDF 947 kb)


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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  • Christine Merk
    • 1
  • Gert Pönitzsch
    • 1
  • Carola Kniebes
    • 1
  • Katrin Rehdanz
    • 1
    • 2
  • Ulrich Schmidt
    • 1
    • 2
    • 3
  1. 1.Kiel Institute for the World EconomyKielGermany
  2. 2.Kiel UniversityKielGermany
  3. 3.Department of Economics and EconometricsUniversity of JohannesburgJohannesburgSouth Africa

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