German citizens ’ preference for domestic carbon dioxide removal by afforestation is incompatible with national removal potential

Ef ﬁ cient and sustainable solutions for offsetting residual emissions via carbon dioxide removal are a major challenge. Proposed removal methods result in trade-offs with other Sustainable Development Goals, and the removal needs of many countries exceed their domestic potentials. Here, we examine the public acceptability of conducting afforestation and direct air capture programmes domestically in Germany or abroad. To uncover the relative importance of various programme attributes, we use a multifactorial vignette experiment. We ﬁ nd that afforestation receives stronger support than direct capture. Next to the costs to households, minimising environmental impacts on biodiversity in forests and the use of renewable energy for direct capture are more important for acceptability than the permanence of storage. Further, individuals strongly prefer domestic programmes to offsets in other countries. These ﬁ ndings suggest signi ﬁ cant discrepancies between strong public preferences for domestic carbon removal with low environmental side-effects and the too low potential for such removals.

T o limit global warming to 1.5 °C, global carbon dioxide (CO 2 ) emissions have to achieve net-zero around 2050.According to estimates by the IPCC 1 , this is beyond reach without the intentional removal of CO 2 from the atmosphere to compensate residual emissions from agriculture, chemical processes, cement production or waste management that cannot be eliminated without shutting down the processes completely.In the Intergovernmental Panel on Climate Change's (IPCC) model pathways that keep warming below 1.5 °C by the end of the century, the estimated amount of global residual emissions varies substantially between 5-16 GtCO 2 in the year when net-zero emissions are reached.After reaching net-zero, additional CO 2 removal might be necessary to balance out a limited temperature overshoot and keep warming below 1.5 °C by the end of the century 1 .Whether this target can be met depends foremost on the speed and extent of emission reduction by transforming the economy and the society, but most likely also on the availability of a portfolio of Carbon Dioxide Removal (CDR) methods that could be deployed at scale and the social license to deploy them.
The ways proposed to remove CO 2 from the atmosphere are diverse and range from reforestation, or ocean liming to direct air carbon capture and storage (DACCS).However, there is no silver bullet, as the large-scale deployment of any of the methods has substantial footprints in terms of land, water, or fertiliser use, biodiversity, and mining, and creates trade-offs with the other Sustainable Development Goals, such as no hunger, clean energy for all, or life on land [2][3][4][5][6][7][8] .While the public is often not yet aware of CDR, such trade-offs and differences in the how, who, and where of CDR deployment might determine public support for or opposition against using the methods in the future.Research has so far mostly looked at the general perceptions of CDR methods, compared different approaches [9][10][11][12] or analysed whether information on trade-offs changes the evaluation 13,14 .
Afforestation is generally well known and viewed positively in the public.Few have heard of DACCS or ocean liming before, and once introduced to these two methods people perceive them more negatively compared to afforestation 9,10,14,15 .A main reason for these differences is whether the approaches are perceived as natural or technical 9,11,13 even though the boundaries between the attributions 'natural' and 'technical' are unclear 16 .It would also be the way how CDR methods are deployed that determines their environmental side-effects and the perceptions of the extent of an interference with natural systems.For example, afforestation, especially in higher latitudes, increases the albedo and requires high nutrient, water, and land inputs with potentially negative effects on biodiversity and food prices 2,4,17 .In comparison, DACCS has a small land footprint but is more expensive, as it requires large amounts of water and energy, which can imply an additional land footprint for energy generation 3,4 .Perceptions elicited in group discussions or deliberations often centre around environmental side-effects, such as pollution or interventions into the natural environment 13,[18][19][20] .CO 2 leakage is one of the main concerns about Carbon Capture and Storage (CCS)-which provides carbon storage for the CDR approaches bioenergy with CCS and DACCS-but study participants are mainly worried about the direct effects on humans and animals at the leakage site, while the negative effect of carbon leakage on the climate or the permanence of storage, i.e., how long it would be stored, are not major concerns 21,22 .Low storage safety is on the other hand rarely mentioned as a risk of afforestation despite the threat of pests, forest fires and droughts.However, the general link to climate action is pertinent, as stronger concerns about climate change have been found to increase the support of CDR 9,14 .
Where CDR methods are deployed, i.e., the location, can influence multiple factors such as the uptake efficiency, costs or the reliability of removal.Global sequestration and storage potentials are unevenly distributed [23][24][25] .Some regions can provide carbon sequestration and storage at much lower cost 23 .Only few European countries have the biophysical capacity to deliver the necessary CO 2 removal 26 .Germany for example could offset the estimated residual emissions in 2045 (36-87 MtCO 2 equ.yr −1 ) by the domestic CDR potential of 68-81 MtCO 2 yr −1 (excluding existing forest sinks).These removals would mainly come from bioenergy with CCS and DACCS [27][28][29] .The estimated removal potential for afforestation on vacant or marginal agricultural land is only small (about 2.6 MtCO 2 yr −1 for Germany in 2050) 29 .Even though the domestic potential in Germany could be sufficient depending on the removal needs, CDR could be done more resource-efficiently abroad than at home where population density and labour costs are high 24,25 .For example, about half of the global reforestation and afforestation potential until 2100 is in Sub-Sahara African and Latin American countries, because per hectare growth and carbon storage potentials are higher compared to boreal forests in temperate climate zones 30 .For the development and deployment of DACCS, Iceland is currently a front runner as both storage capacity and renewable energies are available at lower costs compared to other locations.However, these removal and storage capacities are still minor, and developing them to a significant scale will require massive expansion 31 .The actually available CDR potential might easily fall short of the demand if societal and political support is lacking, domestic CDRprogrammes are not introduced and scaled up early enough or costs are too high.If this is the case, Germany will probably have to rely on buying CO 2 removals from other countries as regulated under Article 6 of the Paris Agreement 32 to meet its nationally determined contributions.The questions of where to compensate domestic emissions and of who should implement the CDR methods raises several questions: Do countries live up to their climate ambitions and their historic responsibility by having the work done in other states 26,33 , or are the actors in other states or at home trustworthy 22,34 ?Therefore, public support of CDR methods can be affected by citizens' trust in countries and institutions.Previous research has also indicated that climate change beliefs 9,14 and social norms 35 might explain public support of CDR; yet it is not clear to what extent this varies with the type of CDR method.
The present research makes two key contributions to the literature: First, while existing works examine public perceptions of various CDR technologies 10,12,14,20,35 , none of them addresses the implications of implementing programmes abroad for their acceptability based on nationwide data.Given the large differences in removal potentials across countries, efficient solutions would require international cooperation which might be difficult to achieve in terms of cross-regional policy frameworks 23 , but also because of the lack of public support.Citizens' support is needed for the compensation of residual emissions with CDR programmes at home and abroad.However, it is an open question to what extent for example trust in institutions abroad 18 and/ or perceptions of national accountability 24,25 affect support.While there is evidence that attitudes toward CDR methods, climate change beliefs and social norms can affect citizens' support, it is not well understood how the impact of these factors affects the perception of different CDR methods.Second, using a multifactorial experiment this research extends beyond the mere acceptability of CDR methods by examining the relative importance and causal effects of the following characteristics of the deployment of afforestation and DACCS on the acceptability of CDR programmes: nationality, environmental impacts, permanence of storage, implementation by public vs. private actors, and household costs.

Results
Acceptability of carbon dioxide removal (CDR) methods.To disentangle the importance of these characteristics, we conducted a multifactorial vignette experiment in late 2020 employing a nationwide survey in Germany.The vignettes differed in several characteristics: nationality of removal/storage site, implementation by public vs. private actors, environmental characteristics (biodiversity for afforestation, energy source for DACCS), permanence of storage and costs to households (see Table 1, Figs. 1  and 2).Before rating the vignettes, respondents received information on climate change, Germany's climate target to reduce emissions to zero, residual emissions, the removal of CO 2 from the atmosphere, afforestation, and DACCS.We then introduced and explained the characteristics that vary between the CDR programmes described in the vignettes (see appendix).Every participant rated three afforestation vignettes and three DACCS vignettes.This was followed by question about their values and attitudes on climate change, the methods and climate action.
We chose the two CDR approaches because they are at the opposite ends of what is perceived as natural, and what is perceived as technical.The levels of the attributes vary the environmental impact via the effects on biodiversity and renewable energy use.The selected host countries vary in the spatial proximity to Germany as the country that commissions the removal, their political stability, and their level of economic development.We make the permanence of storage salient for both options and vary between public vs. private actors as the implementing entity to test whether this co-varies with trust in  The parts of the explanation printed in bold took different levels as presented in Table 1.
Fig. 2 Respondents saw 3 vignettes for Direct Air Capture (DACCS).The parts of the explanation printed in bold took different levels as presented in Table 1.
other countries.We employed an experimental design to generate 48 vignettes for afforestation programmes and 48 vignettes for DACCS programmes, which allow the unconfounded identification of all attribute main effects on acceptability discussed below (see Methods section).Respondents from Germany (n = 1689) rated three (out of 48) afforestation and three (out of 48) DACCS programmes on vignettes.Figure 3 presents the overall acceptability of afforestation and DACCS programmes across all vignettes answered by respondents.They expressed stronger support for afforestation (mean = 5.48, sd = 3.23) than for DACCS (mean = 4.36, sd = 3.10).For afforestation, acceptability is above the midpoint of the scale for 51% of the respondents.For DACCS this figure amounts to 36%.Also, for afforestation in 12% of all evaluations respondents strongly opposed the presented programme (value of 0), and in 14% they fully supported it (value of 10).For DACCS the corresponding values are 18% and 6%, respectively.
Effects of characteristics on CDR methods' acceptability.Figure 4 presents the effects of the attributes on acceptability of afforestation and DACCS programmes (results are robust when excluding respondents who always opted for 0, the lowest acceptance level, see suppl.material, Tables S1 and S2).The results are based on random effects models and indicate that for afforestation, respondents prefer programmes in Germany (the reference category) over other countries, especially Mozambique and Ukraine, but also Australia and Spain.For example, locating programmes in Mozambique or Ukraine leads to a decrease in support by 0.66 and 0.47 scale points, respectively.The difference between Norway and Germany is statistically insignificant.A large positive effect can be observed for the attribute biodiversity.Afforestation programmes with polycultures significantly increase acceptability by 1.63 scale points compared to monocultures (reference category).While the difference between public and private programmes is not statistically significant, we find a positive and statistically significant effect of the guaranteed permanence of carbon storage.Yet, the effect size is rather small; a guaranteed 30-year storage increases support by 0.09 scale points.The costs of afforestation programmes have a strong influence on acceptability.For example, a 10-Euro increase in costs results in a decrease in acceptability by 0.63 scale point, while an increase by 40 Euro translates into a decrease by 2.52 scale points.Fig. 4 Effects of carbon dioxide removal (CDR) characteristics on acceptability of CDR methods.Presented on the y-axis are the effects (dots and 95% CIs) of vignette attributes (country, environmental characteristics, public vs. private, guaranteed permanence of storage, and costs to households, compare Table 1) on changes in support measured on a 11-point scale (x-axis).The results are based on random effects models; n = 5067 vignette evaluations per CDR method from n = 1689 respondents.Positive effects refer to an increase in acceptability and negative effects to a decrease.The effects for the categorical variables (country, public vs private, biodiversity) are relative to the respective base category (Germany, monoculture, private actor).For full regression tables see Tables S1 and S2 in the suppl.material.
A similar pattern emerges for DACCS programmes.Respondents tend to prefer programmes that are implemented in Germany.Yet, only the negative effects for Ukraine and Mozambique are statistically significant at the 5% level (the one for Spain is significant at the 10% level, and the ones for Australia and Norway are insignificant).A higher share of renewable energy increases acceptability.For example, a 10%-increase in the share of renewable energy increases acceptability by 0.17 scale points; 100% renewable energy results in a 1.7 scale point increase.The effects of public vs. private programmes and a longer, guaranteed carbon storage are positive but not statistically significant.Similar to afforestation, we find a large negative cost effect for DACCS.A 10-Euro increase in costs lowers acceptability by 0.51 scale points and a 40-Euro increase by 2.04 scale points.
Effects of individuals' characteristics and attitudes on the acceptability of CDR methods.Our data suggest that respondents' individual characteristics and attitudes matter for their perceptions of CDR methods (the intraclass correlation coefficients for constant-only models are 0.47 for afforestation programmes and 0.53 for DACCS programmes, i.e., 47% and 53% of the variation in acceptability is explained at the individual level and the remaining at the level of vignette attributes).We looked at the importance of trust related to the countries presented in the vignettes and asked our respondents on a four-point response scale (1 = "no trust" to 4 = "very high trust") how much they trust in the political stability and stability of the legal system in each of the countries.With a mean of 3.08 (sd = 0.79), trust in Norway is highest, even higher than the trust in Germany, the respondents' home country (mean = 2.87, sd = 0.86), followed by Australia (mean = 2.79, sd = 0.78), Spain (mean = 2.34, sd = 0.71), Ukraine (mean = 1.70, sd = 0.62) and Mozambique (mean = 1.62, sd = 0.61).While this indicates clear differences between levels of trust in countries, these differences can hardly explain specific country effects in our study.Trust in the political stability and stability of the legal system of a country does not significantly increase the acceptability of CDR programmes in this country (with one exception, all interaction effects between trust and country variables are insignificant at the 5% level, see suppl.material, Table S3).However, there is a general tendency that individuals who trust in the political stability and the stability of the legal system of the respective country express an overall higher acceptability of CDR methods (significant main effects of trust variables, see suppl.material, Table S3).
Beliefs about whether Germany should offset its national residual emissions only in Germany or also abroad have rather notable implications for the acceptability of a host country (see Fig. 5).We asked the respondents on a six-point response scale (1 = "do not agree at all" to 6 = "totally agree") how much they agree with the statement "Germany should offset its residual emissions domestically".The overwhelming majority of respondents (75%) agrees with the statement that emissions should be offset in Germany (values greater than three on the six-point scale, overall mean = 4.23, sd = 1.25).The models in Fig. 5 are in line with the strong preference for Germany in the vignettes.In contrast, those who disagreed that Germany should only compensate at home (25%) are indifferent between countries in the vignettes.This holds true for all countries included in the vignettes, with the exception of Norway where we find no statistically significant difference in the acceptability of programmes in Norway compared to Germany for those who disagree that Germany should compensate at home.This might be explained by respondents' overall very high level of trust in Norway's political stability.
Further analyses, presented in Fig. 6, suggest that the differences in the overall acceptability of afforestation and DACCS programmes can be explained by respondents' attitudes and normative beliefs rather than their socio-economic background.Gender, income, and place of residence (urbanisation) have no significant effect on the support for both afforestation programmes and DACCS.Yet for both CDR methods older respondents expressed significantly lower levels of support than younger respondents (approx.0.17 unit decrease in acceptability for a 10-year increase in age), and for DACCS more highly educated respondents expressed lower support levels than less educated ones (0.28 unit decrease in acceptability); the corresponding effects are statistically significant at the 5% level.We find positive effects for positive attitudes toward afforestation and DACCS based on two items on perceived effectiveness for the compensation of residual emissions and the suitability of the respective CDR method for long-term CO 2 storage.A one-unit increase on the summative 8-point attitude scale results in a 0.25 unit increase in acceptability for afforestation and a 0.72 unit increase for DACCS.Respondents who perceive climate change as a serious problem (climate change belief), perceive positive rewards from friends and family for contributing to climate change mitigation (social norm), and feel a moral obligation to contribute to climate change mitigation (personal norm) express significantly higher acceptability levels than those with lower climate change beliefs and norm perceptions (for DACCS, the climate change belief and the social norm effect are not significant at the 5% level).

Conclusion.
There is increasing recognition for the need to offset residual emissions via CDR to fulfil net-zero commitments 1 .Different methods have been suggested.So-called nature-based solutions for GHG mitigation and CO 2 removal feature prominently in the Nationally Determined Contributions 36 , while only few countries mention more technical methods like DACCS or bioenergy with CCS in their Nationally Determined Contributions 31 .However, large-scale reforestation and afforestation programmes can have negative trade-offs with biodiversity, land-use, food prices, and local livelihoods 5,[37][38][39][40] .In many countries domestic removal potentials will either not be sufficient or compensation could be more resource-efficient abroad than at home, as sequestration and storage potentials are unevenly distributed 24 .Thus, it will likely be necessary to use a portfolio of natural sink enhancement and technical sinks to minimise negative trade-offs with, for example, biodiversity and food security 5,8,41 and to cooperate internationally.
Using a multifactorial vignette experiment, we examine the public acceptability of afforestation and DACCS programmes and the relative importance of various CDR attributes in Germany.In line with previous research 9, 16 , we find that afforestation achieves higher acceptability than DACCS.More specifically, we find that next to low costs to households, limiting negative environmental side-effects, such as avoiding monocultures in afforestation to foster biodiversity and the use of renewable energy for DACCS, are more important for acceptability than the permanence of carbon storage even though long-term removal of CO 2 is the main reason for considering CDR at all.Further, individuals strongly prefer domestic CDR to offsetting emissions in other countries.For both afforestation and DACCS programmes, we find that respondents are cost sensitive as increasing costs lower, all else equal, acceptability.While, in general, trust in host countries' political stability seems to be a relevant factor, the higher acceptability of domestic CDR is rather determined by individuals' strong belief that residual emissions should be offset domestically to take responsibility for the national emissions.
The combination of a preference for afforestation, domestic compensation, high biodiversity, renewable energy (for DACCS), and low costs suggests a significant discrepancy between the need for CDR and a domestic removal potential that matches these public preferences.Forest productivity and the availability of input factors such as cheap renewable energy or land strongly influences the price per removed tCO 2 , therefore densely populated industrialised countries, like Germany, would struggle to compensate residual emissions at home.This incompatibility threatens the feasibility of reaching net-zero targets 42 .
We are the first to show that it matters to people where compensation takes place.In public communications, it is thus important to emphasise the scale of CO 2 removals that would be required domestically: the estimated annual removal of 2.4 MtCO 2 via afforestation and reforestation would require the conversion of 10% of cropland to forests and pastures 29 , and removing 10 MtCO 2 via DACCS would require 3% of the current German energy generation.Considering the currently too low expansion rates of renewable energy generation in Germany and the low geophysical potentials compared to other countries 27 , it becomes clear how big the challenge would be to compensate emissions only domestically, and how important it is to reduce emissions as much as possible.In our study, we did not make these constraints on the domestic potential salient to limit the complexity of the vignettes.In addition, the new energy and security challenges that have emerged since the start of the invasion of Ukraine and the following sharp rise in energy prices suggest that the cost sensitivities observed in our study in 2020 are likely to be much higher in the foreseeable future, limitingnot only-the scope for offsetting residual emissions domestically further.Thus, future research should look more closely at the impact of adding information about these constraints on the Fig. 6 Effects of respondents' individual characteristics and attitudes on the acceptability of CDR methods.Presented on the y-axis are effects (dots and 95% CIs) of respondent characteristics (gender, age, education, income, level of urbanisation of place of residence, attitude toward afforestation/DACCS, climate change concern, social norm perception, and personal norm perception, compare Table 2) on changes in acceptability measured on a 11-point scale (x-axis).Effects of vignette attributes (y-axis) are not shown.The results are based on random effects models; n = 1466.Positive effects refer to an increase in support and negative effects to a decrease.The effects for the categorical variables (woman, higher education) are relative to the respective base category.For full regression tables see Table S3 in the suppl.material.Fig. 5 Effects of carbon dioxide removal (CDR) characteristics on acceptability of CDR methods, depending on whether respondents supported programmes in Germany and abroad (25%) or only in Germany (75%).Presented on the y-axis are effects (dots and 95% CIs) of vignette attributes (country, environmental characteristics, public vs. private, guaranteed permanence of storage, and costs to households, compare Table 1) on changes in support measured on a 11-point scale (x-axis).The results are based on random effects models; n = 409 for the model "Germany and abroad" and n = 1280 for the model "Germany only".Positive effects refer to an increase in acceptability and negative effects to a decrease.The effects for the categorical variables (country, public vs. private, biodiversity) are relative to the respective base category (Germany, monoculture, private actor).For full regression tables see Tables S1 and S2 in the suppl.material.
preferences for characteristics of CDR deployment and also at changes in the acceptability of deep structural transformations.However, in a dialogue with the public these constraints should be made transparent, and it should be emphasised that accountability for national emissions and cost-effectiveness of CDR 35 might only be achievable by also using programmes abroad.The development of the public discourse will show whether the patterns we find in our stated preference experiment also occur in real-world discussions.
Our results offer first insights into the perspective of an industrialised country that would buy carbon offsets abroad, while lacking information about public perceptions and preferences in host countries, where the same preference for domestic action might lead to an opposition against offsetting emissions for other countries 33,43 .Especially in developing countries local communities often do not benefit from carbon market projects 44,45 , and they raise opposition when local livelihoods are threatened 46,47 .Future research should therefore combine insights on preference and acceptance in both carbon offset buying and selling countries to better understand the feasibility of CDR programmes where one country relies on carbon offsets in other countries.

Methods
Vignette specification/attributes Type of CDR.Atmospheric CO 2 is removed either via afforestation/reforestation or DACCS.The acceptability of afforestation is typically highest when several options are assessed, and higher than DACCS and other removal methods 9,10,15 .The perception of the associated risks and the level of tampering with nature is lower for afforestation than for DACCS 9 .
Country where the programme is located.Germany, Norway, Ukraine, Spain, Australia, or Mozambique.We selected countries where CO 2 storage is feasible based on geophysical conditions [48][49][50] .However, the CCS-readiness varies strongly between the countries.Norway and Australia have demonstrations plants, while there are none in Germany, Spain, Mozambique, and Ukraine.In the latter two, the storage capacity is still uncertain 48,50 .While afforestation is feasible in all countries, the uptake potentials are higher in tropical regions compared to temperate climate zones 30 .In addition, the selected countries vary in spatial proximity to Germany, political stability, and economic development.
Implementation by public or private actor.The acceptability and the perception of risks are strongly influenced by the level of trust in the institution or actor responsible for decision making or the implemenation of a project 14,[51][52][53][54] .Overall, the absolute levels of trust in government and firms are similar 54,55 .In previous CCS-projects, the public perceived governments to be influenced by industry 56 , but they had more trust in governments monitoring CCS sites properly compared to firms doing the monitoring 22 .
Guaranteed permanence of storage.A major drawback of afforestation compared to geological storage is the sink saturation over time and the safety of storage.In addition, climate change further increases the risk of a release of the stored carbon due to pests, forest fires or droughts 3,5 .Forest fires could be limited by firebreaks, which, however, reduce the tree-covered area.The storage duration in harvested wood depends on its use and recycling schemes.Altogether, this implies shorter and more uncertain storage durations for afforestation compared to DACCS.The risk of leakage is one of the most important concerns about geological CO 2 storage among laypersons 21 , while this is not a salient concern for afforestation.
Cost to households.Conservative cost estimates for afforestation range between 2 and 150 US$/tCO 2 .They often do not include the cost of forest management over time and could thus be higher 3 .Costs of DACCS per tCO 2 avoided range between 600 and 1000 US$.They strongly depend on the energy source used for the capture.Using natural gas adds an emission penalty of about 30% that could actually render DACCS net positive.Therefore, using renewable energy would increase removal efficiency substantially 3 .Based on this very broad range of cost estimates we choose relatively high monthly costs per household between 5 EUR and 40 EUR (5.7-45.6US$).
Energy source for DACCS.Apart from lower net CO 2 capture, the use of fossil fuels for DACCS would also imply the need for new infrastructure for "old" energy sources.The association with the continued use of fossil fuel has been shown to negatively affect the perception of CCS e.g. when it is coupled with coal-fired power  plants compared to bioenergy with CCS 57 .We thus vary the share of renewable energy for the operation of DACCS programmes from 30 to 100%.
Protection of biodiversity in afforestation.We specified the level of biodiversity of the plantations as either monoculture or polyculture implying a low or a high level of biodiversity.We explain that afforestation means replanting forests without specifying which areas are to be used for this purpose.This means it includes reforestation, i.e., planting on land that was a forest in the last 50 years, and afforestation, i.e., planting on land that has not been forest land before 37 .We also do not specify whether the land has previously been degraded.Plant species richness and the age of the forest can positively influence carbon storage above and below ground, whereas these factors also render forest management more costly and would imply a reduction of commercial logging 58 .The estimated global potential for carbon sequestration is lower when strict sustainability criteria are applied like maintaining protected and undisturbed forests or keeping noncommercial species 3 .
Experimental design.The full factorial-all possible attribute-level combinations -comprises 384 (=6 × 2 × 2 × 4 × 4) possible vignettes for afforestation programmes and 768 (=6 × 4 × 2 × 4 × 4) for DACCS programmes.To reduce the number of vignettes and to allocate attribute levels across vignettes, we opted for a fractional factorial design.The employed fold-over design, with both orthogonality and level balance, allows for separating all main effects from two-way interactions of vignette attributes.This way, attributes are allowed to vary independently of each other.This resulted in 48 vignettes for both afforestation and DACCS programmes.
Respondents were randomly assigned, without replacement, 3 out of 48 afforestation vignettes and 3 out of 48 DACCS vignettes.Presenting them randomly aims to avoid learning and order effects in vignette ratings, and hence attributes can vary independently across vignettes.The total number of vignettes per respondents was limited to six to prevent fatigue.On average, every afforestation vignette and every DACCS vignette was shown 144 times resulting in slightly more than 5000 responses per CDR method.
Sampling and survey.The online survey was conducted in cooperation with the panel provider Respondi between 03 December 2020 and 15 December 2020.
Respondents took a median time of about 15 min to complete the survey.The participants were recruited based on quotas for gender, age groups (>17 years), federal state, and education (low, middle, and high level) that correspond to the distribution in the German population with internet access.Table 2 provides sample characteristics and an overview of variables used in multivariate analyses of the effects of respondent characteristics on CDR acceptability.The age of the participants in the final sample ranges from 18 to 90 years with a mean of 47.7 years.Of the participants 49% are female and 35% have a higher education entrance certificate.

Fig. 1
Fig.1Respondents saw 3 vignettes for afforestation.The parts of the explanation printed in bold took different levels as presented in Table1.

Fig. 3
Fig.3Acceptability of afforestation or DACCS across vignettes.The percentage of respondents who chose a response category from 0 ("strongly oppose") to 10 ("strongly support") in the vignette evaluation task for afforestation and DACCS; n = 5067 vignette evaluations per CDR method from n = 1689 respondents.

1 = totally disagree to 6 =
income per month divided by square root of number of household members, excluding 1% of extreme low and high two four-scale items referring (a) to the effectiveness of afforestation to compensate residual emissions, and (b) the suitability of afforestation for long-term CO 2 storage; higher values indicate a Summative index of two four-scale items referring (a) to the effectiveness of DACCS to compensate residual emissions, and (b) the suitability of DACCS for long-term CO 2 storage; higher values indicate a more positive My friends and relatives are in favour if I contribute to climate protection.(totally

Table 1
Attributes of afforestation and DACCS programmes included in the vignette experiment.

Table 2
Sample characteristics and descriptive statistics.