1 Introduction

Reaching net zero greenhouse gas (GHG) emissions by mid-century and limiting global warming to 1.5 °C will not be possible without the deployment of negative emission technologies (NETs) (IPCC 2018). NETs aim to remove atmospheric carbon dioxide (CO2) and store it permanently (IPCC 2018; Tanzer and Ramírez 2019; Tavoni and Socolow 2013). The process of removing and storing CO2 should not emit more emissions than can be removed to generate negative emissions (Tanzer and Ramírez 2019), which can help balance out unavoidable emissions (Beuttler et al. 2019).

NETs include a range of different measures that vary in terms of their removal processes and storage sites (Meadowcroft 2013). NETs, such as afforestation, remove CO2 out of the atmosphere through photosynthesis, whereas direct air capture and carbon storage (DACCS) removes CO2 directly from the air using a chemical sorbent (Tavoni and Socolow 2013). The removed CO2 is stored either biologically (e.g. soil carbon sequestration [SCS] and biochar) or in deep geological formations (e.g. bioenergy with carbon capture and storage [BECCS]) (Meadowcroft 2013; Tavoni and Socolow 2013).

NETs vary in terms of their levels of technical readiness (Meadowcroft 2013). Some are still at an early stage of research (e.g. ocean fertilization) and not deployed on a large scale (e.g. DACCS), while others are being used today (e.g. afforestation) (Bellamy 2020). In recent years, however, the importance and recognition of the necessity of NETs has been growing, and an increasing amount of scientific literature has been published (Minx et al. 2017). Yet, NETs are still associated with many uncertainties, and their successful large-scale deployment faces several challenges (Bellamy 2020; Fajardy et al. 2019). Some of the main limiting factors for their deployment are water and land availability, energy demand, available storage potential, and high costs (Fajardy et al. 2019; Tavoni and Socolow 2013).

NETs not only face technical, biophysical, ecological, and economic challenges but their deployment is also conditional on public perception and acceptance (Braun et al. 2018; Nemet et al. 2018), which can influence the deployment of NETs via social protests and political processes. Public perception and acceptance may determine whether and by how many people and institutions NETs will be adopted. Hence, public perception and acceptance will be particularly decisive if NETs are implemented on a large scale and their potential side-effects may be considerable (Nemet et al. 2018).

NETs may pose a moral hazard and decrease the public acceptance of mitigation efforts (Campbell-Arvai et al. 2017; Corner and Pidgeon 2014a; Raimi et al. 2019). Further concerns include the influence of different frames or loaded terms, potentially leading to public resistance and polarization (Colvin et al. 2020; Scheer and Renn 2014). Previous research has identified the most common ways of framing NETs in the scientific literature and the media (Bellamy et al. 2012; Huttunen and Hildén 2013; Kreuter 2015), but studies on their influence on public perception and acceptance are still needed (Corner and Pidgeon 2014a; Corner et al. 2012).

In 2019, Switzerland announced a net zero GHG emissions by 2050 target and acknowledged the necessity of NETs to balance out unavoidable emissions from industry, agriculture, and air transportation. Although NETs have become an important instrument in climate policy, several uncertainties remain regarding the actual realizable potential of different NETs in Switzerland (Swiss Federal Council 2020). Nevertheless, Switzerland, with its research and innovation capacity, may become a potential pioneer in the development of NETs, especially with its built-up knowledge on DACCS and biochar (Swiss Federal Council 2020). Climeworks, a Swiss direct air capture company, built the world’s first DACCS plant and proved its technical feasibility and functionality (Beuttler et al. 2019). Further, there exist current Swiss research and development projects on biochar in Switzerland (Beuttler et al. 2019). Hence, it is necessary to press ahead and open-up the public debate on NETs using more deliberative and participatory approaches (Beuttler et al. 2019; Cox et al. 2020). Concerns and opinions of the public should be taken into account in the decision-making processes (Corner et al. 2012).

The present study examines the public perception and acceptance of five specific NETs—BECCS, DACCS, afforestation, biochar, and SCS—in Switzerland. It is one of the first studies to provide a broad overview of the current public perception and acceptance of these five NETs. Moreover, we are the first to investigate how the public perceives three of the most common ways of framing NETs—the technological fix frame, the moral hazard frame, and the climate emergency frame—and how these frames influence the perception and acceptance of NETs.

1.1 Public perception and acceptance of NETs

Prior research on the public perception and acceptance of NETs has focused on geoengineering measures (mainly solar radiation management [SRM]) (Braun et al. 2018; Mercer et al. 2011; Merk et al. 2019; Sütterlin and Siegrist 2017). NETs and SRM are classified as two sub-approaches of geoengineering (IPCC 2018). Several studies on geoengineering have shown that the public generally perceived NETs more positively and accepted than SRM (Braun et al. 2018; Jobin and Siegrist 2020; Scheer and Renn 2014; Wright et al. 2014).

Literature specifically on the public perception of NETs has been scarce (Braun et al. 2018; Wolske et al. 2019). Public awareness of NETs and geoengineering has been shown to be low, as many people have never heard about these measures before (Corner and Pidgeon 2014a; Cox et al. 2020; Jobin and Siegrist 2020; Mercer et al. 2011; Merk et al. 2019; Pidgeon and Spence 2017). This unfamiliarity with NETs could make it difficult for people to decide whether to accept them (Merk et al. 2019; Pidgeon and Spence 2017). However, as NETs have gained increased attention in the scientific literature, the media, and through public engagement processes, awareness has been growing in recent years (Mercer et al. 2011; Scheer and Renn 2014). Furthermore, as NETs are essential in achieving the Paris Agreement targets, they have become an important instrument in climate policy (Swiss Federal Council 2020).

Prior studies have shown that public perception and acceptance varies across different NETs (Braun et al. 2018; Jobin and Siegrist 2020). In general, public support for research on NETs has been shown to be greater than support for their deployment (Jobin and Siegrist 2020; Pidgeon and Spence 2017; Scheer and Renn 2014), although the public’s general support is moderate (Jobin and Siegrist 2020). Afforestation is often perceived as the most accepted NET (Braun et al. 2018; Gregory et al. 2016; Jobin and Siegrist 2020). In comparison, Wolske et al. (2019) and Cox et al. (2020) found no significant difference between the public acceptance of BECCS and DACCS. Wolske et al. (2019) concluded that the public accepted afforestation more, because they perceived it as less tampering with nature than BECCS and DACCS. Simultaneously, afforestation was found to be perceived as less risky and more beneficial than several other NETs (Jobin and Siegrist 2020). Based on this, we investigated the public perception and acceptance of NETs in Switzerland. To provide an initial case study with the aim of more detailed follow-up studies, we focused only on the German-speaking part of Switzerland. BECCS, DACCS, afforestation, biochar, and SCS were chosen as the technologies to be examined based on their importance in previous research as well as their relevance in Switzerland. Switzerland is a pertinent case for such a study, as it is leading in the development of DACCS, and biochar has already been deployed in the country (Beuttler et al. 2019). We did not include ocean fertilization (Switzerland is a landlocked country) or enhanced weathering (most suited to warm and humid areas) (Strefler et al. 2018). More specifically, we explored the following research questions:

RQ1: How familiar is the public with NETs, and what are the public’s first spontaneous associations with NETs?

RQ2: What is the public’s perception of NETs and does it differ across the five NETs?

RQ3: What is the public’s acceptance of NETs and does it differ across the five NETs?

1.2 Framing

The second aim of this study was to investigate differences in the public perception and acceptance of NETs across three of the most common frames found in the scientific literature. Previous studies have hypothesized that framing NETs in different ways can influence the public perception and acceptance of them (Cobb 2005; Corner and Pidgeon 2014b; Corner et al. 2012; Cox et al. 2020; Raimi et al. 2019). Framing refers to the presentation of an issue from one perspective by using a specific conceptualization. Thereby, public perception can be shaped in one direction (Chong and Druckman 2007a). Framing an issue is especially influential when people are unfamiliar with a topic (Amelung and Funke 2015; Cobb 2005; Corner et al. 2012). Since there is an unfamiliarity with NETs among the public, attitudes and opinions toward NETs may be unstable and sensitive to different frames (Mercer et al. 2011; Scheer and Renn 2014). It is thus necessary to choose the terms used to explain and communicate a topic carefully. Especially, it is known that potentially loaded terms such as ‘geoengineering’ can push the public perception of NETs toward resistance and polarization. Hence, research examining which frames are most suitable to avoid polarization and resistance is needed (Colvin et al. 2020).

Previously, several studies have analysed the most common ways in which the term ‘geoengineering’ is framed in the scientific literature (Bellamy 2013; Huttunen and Hildén 2013; Kreuter 2015). When examining these studies, we identified three frames, which we use in our study: (i) the moral hazard frame, (ii) the technological fix frame, and (iii) the climate emergency frame.

Several studies have highlighted that NETs and geoengineering in general may pose a moral hazard (Campbell-Arvai et al. 2017; Corner and Pidgeon 2014a; Lin 2013; Raimi et al. 2019). This implies that the public perceives such technologies as an excuse to avoid mitigating climate change through political efforts to reduce emissions or individual lifestyle changes (Corner and Pidgeon 2014a). The moral hazard argument has previously been confirmed by two studies, which found that learning about NETs reduced the public acceptance of mitigation by decreasing people’s perception of the threat of climate change (Campbell-Arvai et al. 2017; Raimi et al. 2019).

When analysing the most common frames of geoengineering used in the scientific literature, Huttunen and Hildén (2013) found that one frequently used frame revolves around geoengineering being a technological fix. This frame emphasizes that geoengineering is a valid third option for combating climate change in addition to emission reduction measures and lifestyle changes (Huttunen and Hildén 2013).

Bellamy (2013) found that one of the main ways of framing geoengineering emphasizes that these measures can be used in the case of a climate emergency. Geoengineering serves as a last resort once a climatic tipping point is crossed, and abrupt and dangerous climatic events will occur (Bellamy 2013; Huttunen and Hildén 2013). Thus, geoengineering will only be used if mitigation fails to achieve sufficient emission reductions (Crabbe 2009).

The Swiss government describes NETs as a complementary measure to emission reduction measures rather than a substitute for mitigation efforts (Swiss Federal Council 2020). Similarly, two previous studies found that the UK public emphasizes the importance of using geoengineering as complementary to mitigation (Corner et al. 2013; Corner and Pidgeon 2014a).

Prior framing experiments on NETs have been scarce and focused mostly on SRM. Two studies, however, analysed the effect of framing geoengineering as ‘natural’ (Corner and Pidgeon 2014b; Mahajan et al. 2018). Mahajan et al. (2018) found that framing SRM using a volcano eruption analogy did not significantly influence the public acceptance of SRM in comparison to framing SRM as an artificial process. In contrast, Corner and Pidgeon (2014b) found that framing geoengineering using a natural analogy significantly increased the public acceptance of geoengineering. Additionally, several studies have focused on the differences in the public perception and acceptance of NETs when providing participants with different amounts of information (Braun et al. 2018; Mercer et al. 2011; Sütterlin and Siegrist 2017; Wolske et al. 2019). Wolske et al. (2019) and Braun et al. (2018) both detected that providing information about NETs and their potential risks decreased public acceptance of these measures. Sütterlin and Siegrist (2017) concluded that briefly providing participants with information on SRM led to a more negative perception. Mercer et al. (2011), however, found that including an educational section in their survey did not have a significant effect on the public acceptance of SRM.

Although the results of previous studies revealed framing effects on the public support for NETs and certain climate policies (Braun et al. 2018; Corner and Pidgeon 2014b; Lockwood 2011; Wolske et al. 2019), there also exist studies indicating opposite results (Bechtel et al. 2015; Bernauer and McGrath 2016). Bernauer and McGrath (2016) for example found no evidence that framing climate policy in different ways (good society, economic co-benefits, and health benefits frame) increases public support.

Thus far, only a few studies have focused on analysing the effect of framing geoengineering as a moral hazard (Corner and Pidgeon 2014a; Whitmarsh et al. 2019), and more research on these framing effects is needed (Corner and Pidgeon 2014a; Jobin and Siegrist 2020; Visschers et al. 2017). Therefore, we conducted a framing experiment with three of the most common ways of framing NETs and examined the following research questions:

RQ4: Does public opinion, perception, and acceptance differ across the three frames?

  1. a.

    What is the public’s opinion of the moral hazard frame, technological fix frame, and climate emergency frame?

  2. b.

    How do the moral hazard frame, technological fix frame, and climate emergency frame affect the public perception and acceptance of NETs?

Whitmarsh et al. (2019) investigated the influence of framing carbon capture and storage (CCS) as a substitute for mitigation and lifestyle changes vs. as an addition to lifestyle changes, finding that the acceptance level of CCS was not significantly different between these two frames (Whitmarsh et al. 2019). Similar results were obtained by the study of Corner and Pidgeon (2014a), who discovered no significant influence of framing geoengineering as a moral hazard on public acceptance compared to a counter moral hazard frame or no frame. Visschers et al. (2017) observed that the belief that SRM poses a moral hazard led to a higher acceptance of SRM in the USA, UK, Canada, China, and Germany, but did not significantly influence the acceptance of SRM in Switzerland. Based on these findings, we postulate the following:

H1: Public acceptance will not differ between the moral hazard frame and the technological fix frame.

The results of a previous study by Amelung and Funke (2015) showed that framing geoengineering as a ‘plan B’ if mitigation fails increased public acceptance of geoengineering. Corner et al. (2011) found that the climate emergency frame is likely to enhance the perceived legitimacy of geoengineering, since this frame stresses the necessity of geoengineering. Climate emergency therefore acts as a frame that ‘is likely to have artificially enhanced the acceptability of conducting research into these technologies’ (Corner et al. 2011, p. 14). Based on these studies, we postulate the following:

H2: The climate emergency frame will increase the public perception and acceptance of NETs in comparison to the other two frames.

2 Methods

2.1 Setting and participants

We conducted an online survey in the German-speaking part of Switzerland in June 2020 to fill this research gap. Participants were recruited through the ISO-accredited polling company, Respondi. A total of 693 Swiss citizens completed the survey and passed the quality test, which set a time minimum of five minutes to answer the survey, in order to eliminate meaningless data (Leiner 2013). Fifty-seven individuals did not pass the time minimum, and 464 were eliminated while taking the survey because they failed the manipulation check. The manipulation check was adapted from Whitmarsh et al. (2019) and assessed whether the participants read and understood the assigned frames.

Regarding age and gender, a balanced and representative sample was achieved through quota sampling. The final sample’s gender ratio was representative of the Swiss population, as 50.8% were women (49.2% male) (FSO 2020b). The average respondent age of 48 years (SD = 15.57) was slightly higher than the average age in Switzerland reported by the Swiss Federal Statistical Office (FSO 2019). In comparison with the average educational attainment of the Swiss population, the final sample had a higher level of education (FSO 2020a) (Table B-1, online appendix B). The sample characteristics—age, gender, education, political orientation, concern about climate change, environmental identity, and technology commitment—did not significantly differ across the five NETs or across the 3 (frames) × 5 (NETs) sample groups.

2.2 Design, materials, and procedure

The online survey was programmed in Unipark and pre-tested in order to improve the clarity of the questions and the technical functionality (see survey in online appendix A). We used a between-subjects design to randomly assign participants to one of 15 groups according to a 3 (frames) × 5 (NETs) factorial design.

Participation in the online survey was voluntary, and participants had to give their informed consent before starting the survey. Participants were first asked about their familiarity with NETs in general on a scale adapted from Whitmarsh et al. (2019), ranging from 1 (never heard of it) to 5 (know a lot about it). Secondly, participants stated their first spontaneous associations when thinking about NETs. Thirdly, we measured participant’s first affective evaluation of NETs in general using a seven-point scale, adapted from Pidgeon and Spence (2017).

An information section followed, in which participants first read an introduction about climate change—adopted from Jobin and Siegrist (2020)—and a short general definition of NETs. Participants were then randomly allocated to one of the three frames and instructed to read the assigned frame. The frames were formulated using language without technical terms and based on expressions found in previous literature (Bellamy 2013; FOEN 2020; Whitmarsh et al. 2019).

Moral hazard frame

NETs offer us the solution for reducing climate change. This means that we do not have to reduce our emissions or change our way of life.

Technological fix frame

NETs are not a substitute for reducing emissions and changing our way of life. To reduce climate change, we must use NETs in addition to today’s measures.

Climate emergency frame

NETs offer us an emergency option for reducing climate change. We will only use them if reducing emissions and changing our way of life are not sufficient.

Participants were instructed to evaluate the frames according to five characteristics—bad vs. good, unrealistic vs. realistic, unclear and difficult to understand vs. clear and easy to understand, unbelievable vs. believable, worrying vs. reassuring, and not convincing vs. convincing—on a seven-point scale. This served to examine how the Swiss public perceives the frame applied by the Swiss government (technological fix frame) compared to contrasting frames.

Next, participants were randomly allocated to one NET and correspondingly viewed a picture of the assigned NET and read a related description. The descriptions of the NETs were adapted from Jobin and Siegrist (2020), and the pictures were designed based on a publication by the Mercator Research Institute on Global Commons and Climate Change (MCC 2016).

The next part of the survey included the variables tampering with nature, trust in responsible actors, perceived risks and benefits, support for NETs, and a second affective evaluation, always regarding the assigned NET. We measured how much participants perceived the assigned NET to tamper with nature using five items adapted from Jobin and Siegrist (2020) and Wolske et al. (2019) on a seven-point Likert scale. Participants had to indicate the degree to which they trusted different organizations regarding the use of the assigned NET to reduce climate change on a five-point scale adopted from Jobin and Siegrist (2020). The perceived risks and benefits of NETs were measured with 10 items adopted from Jobin and Siegrist (2020) on a seven-point Likert scale. Participants were further asked to weigh the risks of the assigned NET against its benefits. Answer choices were adopted from Whitmarsh et al. (2019) and included five options. Analysing the reliability of the measured scales both for each specific NET and across the sample showed that it was in an acceptable to good range (0.76 ≤ α ≤ 0.90) for all variables (Table B-2, online appendix B).

Support for research on and deployment of NETs were indicated on a six-point scale based on Jobin and Siegrist (2020). Additionally, participants’ opinions regarding the deployment of their assigned NET were measured according to five characteristics adopted from Wolske et al. (2019). The second affective evaluation after the information section was measured at a NET-specific level (= specific affective evaluation) and again for NETs in general (= general affective evaluation) (Pidgeon and Spence 2017).

The last part of the survey included following three variables: participants’ concern about climate change (adopted from Jobin and Siegrist 2020), their environmental identity (adopted from Whitmarsh et al. 2019), and their technology commitment (adopted from Neyer et al. 2016). Each variable included several items that had to be rated on a seven-point Likert scale. The reliability of these three variables was in a good to excellent range (0.87 ≤ α ≤ 0.92). We further collected the demographic data of the participants, including their educational qualification, canton of residence, and political ideology, on a scale from 1 (left) to 9 (right) (Breyer 2015). Finally, participants could state their concluding remarks and were then debriefed on the study design. Specifically, participants could read the two frames to which they were not assigned in order to minimize the impact of the assigned frame on their opinions in the real political discussion.

Data from the online survey was analysed using SPSS. We conducted multiple one-way analyses of variance (ANOVAs) to test for differences between the five NETs/the three frames and used Bonferroni post hoc tests to compare pairwise for significant differences. To examine the magnitude of the detected differences, we calculated the respective effect sizes by using η2 or Cohen’s d. To analyse RQ2 and RQ3, we aggregated respective answers over the three frames (total sample) to explore general response patterns toward NETs (Sections 3.2 and 3.3).

3 Results

3.1 RQ1: Familiarity with NETs

Most participants indicated a high general unfamiliarity with NETs, with most of the participants having not yet heard about NETs (n = 324, 46.8%). Most of the remaining participants had already heard the term ‘NET’ (n = 221, 31.9%), whereas some knew a little about the topic (n = 128, 18.5%); only 2.5% (n = 17) knew a fair amount. Lastly, only two participants (3%) indicated they knew a lot about NETs.

Participants also indicated a spontaneous association or thought they had when thinking about NETs. To analyse the answers, we coded them by using 25 categories (Table B-3, online appendix B). The three most often mentioned categories were unfamiliarity with the topic (14.7%), emissions and pollution (13.5%), and CO2 recovery and emission removal (11.3%). Several participants pointed out the ambiguous term ‘NET’, stating that they were not sure whether the word ‘negative’ refers to the emissions or the technologies. Further, the word ‘negative’ was associated with something bad or harmful.

3.2 RQ2: Public perception of NETs

To analyse RQ2, we aggregated the respective results across the three frames (total sample) and found that participants evaluated all five NETs moderately. Paired-sample t-tests showed that participants evaluated NETs significantly more positively after the information section than before (all ps < 0.001, 0.48 ≤ Cohen’s d ≤ 0.86) (Fig. 1). We further tested for the difference between participants’ specific affective evaluation of the assigned single technology and their affective evaluation of NETs in general and found that the differences were only significant for BECCS (t(137) = 3.12, p = 0.002, Cohen’s d = 0.27), DACCS (t(133) = 2.43, p = 0.016, Cohen’s d = 0.21), afforestation (t(139) = −6.62, p < 0.001, Cohen’s d = 0.56), and biochar (t(139) = 3.52, p = 0.001, Cohen’s d = 0.30). For BECCS, DACCS, and biochar, participants evaluated the assigned NET significantly less positive than NETs in general, although these effects were small. On the contrary, a moderate effect showed that participants evaluated afforestation significantly more positive than NETs in general (Table 1). Several one-way ANOVAs tested for differences in participants’ affective evaluations of the five NETs (Table 1). The results indicated that participants’ general (F(4,688) = 3.15, p = 0.014, η2 = 0.018) and specific (F(4,688) = 28.51, p < 0.001, η2 = 0.142) affective evaluations after the information section significantly differed across the five NETs. Bonferroni post hoc tests showed that participants’ general affective evaluation after the information section was significantly more positive for afforestation than for DACCS (p = 0.009) and that their specific affective evaluation was significantly more positive for afforestation in comparison to all the other NETs (all ps < 0.001).

Fig. 1
figure 1

Means of the general affective evaluation before and after the information section, shown across the five NETs for each of the three frames and aggregated for the total sample. Both variables measured the affective evaluation on a scale from 1 (very negatively) to 7 (very positively). NETs with a significant difference (p < 0.001) between the general affective evaluation before and after the information section (total sample) are marked with *. Error bars represent 95% confidence intervals (see Table B-4 in online appendix B for exact numbers)

Full size image
Table 1 Perceived risks and benefits, tampering with nature, and general and specific affective evaluations after the information section for the five NETs
Full size table

We further examined differences in public perception across the five NETs (Table 1). Participants’ trust in responsible actors regarding the use of the assigned NET to reduce climate change did not significantly differ across the five NETs (F(4,688) = 0.64, p = 0.634). Participants perceived the variable tampering with nature, however, significantly different across the five NETs (F(4,688) = 23.02, p < 0.001, η2 = 0.118). Bonferroni post hoc tests indicated that participants perceived afforestation to tamper with nature significantly less than the other NETs (all ps < 0.001). They perceived DACCS to more significantly tamper with nature than biochar and SCS (both ps < 0.001). Participants also perceived the benefits (F(4,684) = 25.59, p < 0.001, η2 = 0.130) and risks (F(4,683) = 38.75, p < 0.001, η2 = 0.185) of NETs significantly different across the five NETs. Additionally, participants perceived afforestation significantly more beneficial and significantly less risky than the other five NETs (all ps < 0.001). Participants indicated that, for afforestation, the benefits outweighed the risks significantly more (all ps < 0.001) than for the other five NETs (Table B-5, online appendix B). Participants perceived DACCS significantly less beneficial than BECCS (p = 0.045) and SCS (p = 0.040) and significantly more risky than SCS (p = 0.024).

3.3 RQ3: Public acceptance of NETs

To analyse RQ3, we aggregated the respective results across the three frames (total sample) and found a significant difference between participants’ support for research and the support for the deployment of NETs (t(692) = 3.38, p = 0.001, Cohen’s d = 0.13). Measured on a NET-specific level, the differences between the two variables were significant for DACCS (t(133) = 3.32, p = 0.001, Cohen’s d = 0.29) and biochar (t(139) = 2.26, p = 0.026, Cohen’s d = 0.19). Although in each case participants’ support was significantly higher for research than for deployment, these effects were very small (Fig. 2). We tested for differences in participants’ support across the five NETs and found a moderate difference for participants’ support for research (F(4,688) = 8.26, p < 0.001, η2 = 0.046) and a small difference for participants’ support for deployment (F(4,688) = 13.65, p < 0.001, η2 = 0.074). Bonferroni post hoc tests indicated that both participants’ support for research and their support for deployment were significantly higher for afforestation than for all other NETs (all ps ≤ 0.001).

Fig. 2
figure 2

Means of the support for research and support for deployment, shown across the five NETs for each of the three frames and aggregated for the total sample. Both variables measured participants’ support on a scale from 1 (strictly reject) to 6 (fully support). NETs with a significant difference (p < 0.05) between the support for research and the support for deployment (total sample) are marked with *. Error bars represent 95% confidence intervals (see Table B-6 in online appendix B for exact numbers)

Full size image

We measured participants’ opinions regarding the deployment of the five NETs based on five different characteristics. One-way ANOVAs revealed that participants perceived all five characteristics significantly different across the five NETs (Table B-7, online appendix B). Bonferroni post hoc tests showed that participants perceived afforestation significantly more frequently as a good idea, as practical, as a smart investment, as wise, and as acceptable than the other four NETs (all ps < 0.001). Simultaneously, they perceived SCS (M = 4.77, SD = 1.39) as significantly more practical than DACCS (M = 4.25, SD = 1.54, p = 0.028).

3.4 RQ4: Differences in public opinion, perception, and acceptance across the three frames

Participants evaluated the assigned frames with open comments (Table B-9, online appendix B) and regarding five specific characteristics. One-way ANOVAs tested for differences between participants’ evaluation of the three frames (Table B-8, online appendix B), and revealed that participants’ perception of all five characteristics differed significantly between the three frames (all ps ≤ 0.017, 0.012 ≤ η2 ≤ 0.109). Bonferroni post hoc tests indicated that participants perceived the moral hazard frame (M = 3.90, SD = 1.74) significantly less credible than the other two frames (both ps ≤ 0.036). Participants perceived the climate emergency frame (M = 4.28, SD = 1.59) significantly less credible than the technological fix frame (M = 5.25, SD = 1.51, p < 0.001). Participants found the technological fix frame (M = 4.98, SD = 1.44) significantly more realistic than the moral hazard frame (M = 3.66, SD = 1.72) and the climate emergency frame (M = 4.01, SD = 1.62) (both ps < 0.001). They evaluated the climate emergency frame (M = 4.41, SD = 1.79) as significantly less clear and easy to understand than the technological fix frame (M = 5.00, SD = 1.78, p = 0.001). Participants also perceived the climate emergency frame (M = 3.96, SD = 1.56) significantly more worrying than the technological fix frame (M = 4.37, SD = 1.46, p = 0.014). Finally, participants evaluated the technological fix frame (M = 5.10, SD = 1.49) significantly more convincing than the moral hazard frame (M = 3.82, SD = 1.79) and the climate emergency frame (M = 4.12, SD = 1.64) (both ps < 0.001).

To test for differences in the public perception and acceptance of NETs across the three frames (Table B-10, online appendix B), we used several one-way ANOVAs. Results showed that participants’ affective evaluation did not differ significantly between the three frames (F(2,690) = 1.66, p = 0.191) (Fig. 1). We further found that the perceived risks (F(2,685) = 0.22, p = 0.800) as well as the perceived benefits (F(2,686) = 0.19, p = 0.827) of NETs did not significantly differ between the three frames. Our findings also confirmed that participants’ weighing of the risks against the benefits of NETs did not significantly differ between the frames (F(2,690) = 1.60, p = 0.202). Furthermore, participants’ support for research (F(2,690) = 0.00, p = 0.998), their support for deployment (F(2,690) = 0.00, p = 0.998), and their overall support of NETs (F(2,690) = 0.00, p = 1.000) did not significantly differ between the three frames (Fig. 2). Participants’ opinions regarding the deployment of NETs were also not significantly different across the three frames (all ps > 0.05). Moreover, we found no differences between frames for the abovementioned variables when testing on a NET-specific level (Table B-10, online appendix B).

4 Discussion

4.1 Key findings

The aim of our study was to examine the current public perception and acceptance of five NETs—BECCS, DACCS, afforestation, biochar, SCS—in Switzerland. We investigated differences in public perception and acceptance across the three most common frames by applying a between-subjects design. In line with previous research (Cox et al. 2020; Jobin and Siegrist 2020; Merk et al. 2019; Pidgeon and Spence 2017), we found a high unfamiliarity with NETs among the Swiss public, with most participants having never heard about NETs before. This was also reflected in participants’ spontaneous associations with NETs at the start of the survey, where many participants linked NETs to a range of unrelated topics, such as transportation and 5G. Compared to a study conducted in the USA by Wolske et al. (2019), we found that the public’s unfamiliarity with NETs was as high as in the USA. However, the study of Cox et al. (2020) indicated a slightly higher familiarity level in the USA and in the UK than we found in Switzerland.

In our study, participants’ first affective evaluation of NETs tended toward the middle of the scale. In contrast to the study of Sütterlin and Siegrist (2017), our study showed that providing participants with information on NETs led to a more positive evaluation of them, which was measured as a medium to large effect. We found that participants first make incorrect associations of NETs and evaluate them negatively. Participants who were more familiar with NETs and spontaneously associated them with CO2 recovery/removal or with specific NETs evaluated NETs more positively. Hence, Swiss people evaluate NETs more positively when they have a basic understanding of NETs.

The affective evaluation also differed largely between the five NETs. Afforestation stood out as the most positive NET and was perceived more practical, wise, and acceptable as well as a better idea and a smarter investment than the other four NETs. This explains why afforestation was already found as the most favoured NET in previous studies (Braun et al. 2018; Gregory et al. 2016; Jobin and Siegrist 2020). We found that participants who read an explanation of afforestation perceived NETs in general more positively than participants who read an explanation of DACCS.

In line with prior research (Jobin and Siegrist 2020; Wolske et al. 2019), afforestation was perceived the least risky, most beneficial, most accepted, and the least to tamper with nature. However, different from the study of Jobin and Siegrist (2020), DACCS was perceived as riskier, less beneficial, and as more significantly tampering with nature than SCS. Simultaneously, DACCS was perceived as less beneficial than BECCS and as tampering more significantly with nature than biochar. However, the findings of Wolske et al. (2019) and Cox et al. (2020) that the public support does not significantly differ between BECCS and DACCS were confirmed by our results.

In general, we found no strong opposition against NETs in Switzerland. Our results confirm previous findings that public support for research is higher than their support for the deployment of NETs, although this effect was very small (Jobin and Siegrist 2020; Pidgeon and Spence 2017; Scheer and Renn 2014). The support for research on and deployment of NETs was, however, not very high, which was also observed by another study (Jobin and Siegrist 2020). There still exist several uncertainties and concerns regarding NETs among the Swiss public. Simultaneously, there is a high general unfamiliarity with NETs, which may have led to difficulties for participants in deciding on whether to accept NETs (Merk et al. 2019; Pidgeon and Spence 2017).

Previous research has identified that the public perception and acceptance of NETs can differ between countries (Sugiyama et al. 2020; Visschers et al. 2017). While the USA and UK public tend to perceive DACCS negatively and BECCS neutrally (Cox et al. 2020), we found that the Swiss public was more likely to perceive BECCS and DACCS positively. Compared to a study in the USA by Wolske et al. (2019), which used the same scale to measure the public opinion regarding the deployment of NETs, DACCS is perceived less positively in Switzerland. Afforestation is perceived slightly more positively in the USA, whereas the public opinion on the deployment of BECCS is the same as in Switzerland (Wolske et al. 2019). Further, in Switzerland, slightly more people tend to support afforestation than in Germany (Braun et al. 2018).

In general, the evaluation of the three frames was moderate, especially for the climate emergency frame. The moral hazard frame was perceived as the least credible and the technological fix frame as the most credible. Additionally, the technological fix frame was perceived as the most realistic and most convincing frame. Thus, the Swiss public generally shares the opinion of the Swiss government, which describes NETs as a complementary measure to mitigation (Swiss Federal Council 2020). The public’s emphasis on the importance of mitigation and the use of NETs as a complementary measure has already been identified in previous research (Corner et al. 2013; Corner and Pidgeon 2014a). Consistent with previous studies, we find that the public raises concerns that NETs are not addressing the cause of climate change but rather only deal with its ‘symptoms’ (Cox et al. 2020). The Swiss public perceived the climate emergency frame not only as the most worrying frame but also as the most difficult to understand. Participants had difficulty understanding what the mentioned emergency option was referring to, which was reflected in a few of the open comments, which said that the frame was formulated too difficult or not concrete enough. Similar concerns regarding the climate emergency frame were raised by Horton (2015), who specified that ‘climate scientists have no agreed definition of what would constitute a climate emergency’ (Horton 2015, p. 148).

As found by previous studies (Bechtel et al. 2015; Bernauer and McGrath 2016), our results show that there are no framing effects on the public perception and acceptance of NETs. As the public perception and acceptance did not differ between the moral hazard frame and the technological fix frame, our first hypothesis is confirmed. This finding is in line with previous studies by Whitmarsh et al. (2019), Corner and Pidgeon (2014a), and Visschers et al. (2017). However, our second hypothesis is not supported by our results, as the climate emergency frame did not significantly increase the public perception and acceptance of NETs. This contrasts with the studies by Amelung and Funke (2015) and Corner et al. (2011), both of which concluded that framing geoengineering as a climate emergency led to an increase in public support. However, the studies of Amelung and Funke (2015) and Corner et al. (2011) focused on SRM, which is generally less supported by the public than NETs (Braun et al. 2018; Wright et al. 2014). As many Swiss people already recognize the necessity of NETs, their level of support was not affected by reading about the climate emergency frame in the present study.

We found that people’s perception and acceptance of NETs are not influenced when NETs are illustrated in different ways. It could be that the three frames were not formulated strongly and concisely enough or that the differences between the frames were so small because results generally tended toward the middle due to the high unfamiliarity with NETs. Further, as we only compared results across the three frames, it is possible that all frames influenced the public perception and acceptance in the same direction, resulting in insignificant differences across frames (Chong and Druckman 2007b). An explanation from a previous study also indicates that public support for climate policy may not be altered by simple information frames, as other factors (e.g. demographics, values) have a greater influence (Bernauer and McGrath 2016).

In several open comment sections of the survey, one issue was mentioned repeatedly: the ambiguity of the term ‘NET’. Participants were not sure whether the word ‘negative’ referred to the emissions or the technologies and some participants spontaneously associated NETs with technologies emitting a lot of emissions. The word ‘negative’ was understood as something bad or harmful instead of indicating below zero emissions. This misinterpretation of the term ‘NET’ may also explain why participants’ first affective evaluation was more negative than the one after participants read a basic explanation of NETs. Similarly, studies on geoengineering have observed that geoengineering is often associated with terms that sound similar, e.g. ‘geotechnical engineering’ (Mercer et al. 2011; Pidgeon et al. 2012). Hence, both terms—‘geoengineering’ and ‘NET’—are ineffective at communicating the topic and lead to misunderstandings (Mercer et al. 2011; Pidgeon et al. 2012). Alternative terms like ‘greenhouse gas removal’ and ‘carbon dioxide removal’ might be more appropriate.

4.2 Policy implications

When discussing the policy implications of our findings, it should be noted that we focused on the German-speaking part of Switzerland and that it may therefore be difficult to draw federal policy conclusions. Nevertheless, our results provide a good first insight into possible policies for the future development of NETs in Switzerland. First, our findings confirm the Swiss public’s unfamiliarity with NETs and, second, indicate that the public perceived NETs generally neutrally, with more positive evaluations of NETs after participants read a basic explanation of NETs. Third, no strong opposition was found against NETs, as we discovered a moderate public acceptance across all five NETs. From a policy point of view, this implies that public perception and acceptance are currently not polarizing factors that would strongly inhibit further research on and deployment of NETs in Switzerland.

Our results also suggest that a broadening of the public acceptance of NETs could build on the specific acceptability of afforestation, since those who understand afforestation as a NET have a more positive affective evaluation of NETs in general. However, afforestation faces other challenges, as factors such as reversibility, sink saturation, and land availability may hinder policymakers from implementing afforestation (Fuss et al. 2018), especially since its potential in Switzerland seems to be rather low (Beuttler et al. 2019). Further, we found no large differences in the perception and acceptance of the five different NETs. This indicates that, in Switzerland, it is conceivable to further investigate and deploy several NETs in parallel. Since, except for afforestation, there were no clear favoured NETs in terms of public perception and acceptance, Switzerland can devote more attention to determining which NETs are the most effective and efficient in terms of their technical, biophysical, ecological, and economic characteristics.

We found that the public perception and acceptance of NETs does not differ between the three frames. There could be several reasons for this, which must be further examined in future research. However, it implies that, at this stage, the perception and acceptance of NETs in Switzerland are neither enhanced nor diminished by these three frames and that none of the frames leads to strong public opposition or resistance.

We observed that the technological fix frame best reflected the public opinion in Switzerland. At the same time, the public recognized the potential of implementing NETs as a complementary measure to current emission reduction efforts. Therefore, it is of critical importance that Switzerland does not decrease its efforts toward emission reduction. As there are still many uncertainties linked to the research on and deployment of NETs, it remains important to continuously involve the public along the way in their development process. The public may currently accept NETs, but concrete large-scale projects may change this in the future. Additional research will therefore need to continuously monitor how the public perceives the risks and benefits of large-scale deployment projects.

4.3 Limitations and future research

At first, we note that our survey did not examine participants’ familiarity with a specific NET. Hence, we cannot say if the Swiss public’s familiarity differed between the five NETs. However, a previous study by Jobin and Siegrist (2020) measured Swiss citizen’s familiarity with the five NETs included in our study. Comparing their results to the general familiarity with NETs measured by our study, we conclude that Swiss citizens are much more familiar with afforestation than with any other NET or NETs in general. We thus hypothesize that many Swiss citizens are unfamiliar with the term ‘NET’, but may know one specific NET.

Our survey was limited in its design by the lack of a control group that was not exposed to any frame. Such a control group could have served as a baseline of comparison and provided more insights into the framing effects. We also note that all participants were asked the questions in the same order. Since preceding questions may influence participants’ responses to subsequent questions, there is a possibility that our results may have been biased by question order effects (Rasinski et al. 2012). Related to this, the manipulation check and participants’ evaluation of the frames may have influenced the framing effects. Our results may have also been biased due to eliminating participants who failed the manipulation check. Eliminating participants due to such post-treatment manipulation checks has been shown to significantly alter results and may lead to weaker findings (Aronow et al. 2019; Montgomery et al. 2018).

Further, our study did not provide participants with information regarding the benefits and risks of NETs, as we focused on explaining the main process of NETs. Previous studies have observed that informing the public about the risks and benefits decreases their acceptance of NETs (Braun et al. 2018; Sütterlin and Siegrist 2017; Wolske et al. 2019). Future studies should thus examine which factors are most decisive for public acceptance and which risks people may be more willing to accept.

Our study was limited in its quantitative design. Although this gave us a large sample size and allowed us to gather a lot of data, participants’ unfamiliarity with NETs may have led to an overuse of the midpoint of the scales. To address such biases and explore participants’ thoughts and opinions more thoroughly, more qualitative research is needed. The importance of participatory and deliberative approaches in facilitating more nuanced opinions and debates has also been highlighted by previous studies (Corner et al. 2012; Cox et al. 2020; Whitmarsh et al. 2019).

As our study was limited to the German-speaking Swiss population, the generalizability of our results might also be limited to this part of Switzerland. Although previous studies have found cross-cultural and cross-country differences (Sugiyama et al. 2020; Visschers et al. 2017), our results show only minor differences compared to other studies from Europe and North America. Thus, a generalization to other Western countries with similarly low public awareness of NETs seems possible. To further examine cross-cultural (e.g. different regions in Switzerland) and cross-country differences, more follow-up studies should be conducted.

5 Conclusion

To limit global warming to 1.5 °C and achieve net zero GHG emissions by the mid-century, NETs have become indispensable. As the importance of NETs as a climate policy instrument is growing, it is crucial to regularly examine the public perception and acceptance of NETs worldwide. As our findings indicate, the Swiss public is still very unfamiliar with NETs and generally evaluates them neutrally. However, the public also tends to accept NETs and acknowledges the importance of implementing NETs as complementary to current emission reduction efforts. In the future, the public debate on NETs should be broadened and intensified by involving the public along the way of the large-scale development of NETs.