The Five Canadas of Climate Change: Using audience segmentation to inform communication on climate policy

reduce greenhouse gas and address climate change?” Results from exploratory factor analysis suggested that these three items were not distinct enough to be discussed separately. In fact, the three items loaded onto a single factor that accounted for 71% of the variance (S1 Table in S1 File). All three questions (i.e., perceived fairness, perceived effectiveness and willingness to pay for carbon pricing) were converted on a 0–1 scale, summed and divided by three to form an index ranging from 0 (“highly unsupportive of carbon pricing”) to 1 (“highly supportive of carbon pricing”). The index had a Cronbach’s alpha of 0.79, indicating good internal consistency. We measured several demographics, including age, gender, education, language, region, interest in politics and party identification. We also included a measure of political ideology as a covariate for this study, measured with the question “Generally speaking, do you usually con- sider yourself as being at the left, the right or the centre of the political spectrum?” Including a small number of covariates in the analysis of an experiment can increase the precision of esti- mates by reducing noise, especially when the number of observations is small, as long as covar- iates are selected in advance and good theoretical reasons suggest that these covariates will influence the dependent variable significantly [71]. In line with this–and considering the abun- dance of research suggesting that people identifying with the ideological left are more likely to

support climate policies [4, 72, 73]–political ideology was included as a covariate in our mod- els. All measures with exact wording and descriptive statistics can be found in the S1 File. We ran one-way ANOVAs to determine if there were any significant imbalances across groups in terms of observed variables including age, education and gender, and found no sig- nificant differences, confirming experimental balance across groups on these observed charac- teristics (S2 Table in S1 File). Finally, we conducted a sensitivity analysis using G�Power [74] to estimate the effect sizes that could be detected with a power of 80% given the size of our sample and an alpha level of 0.05. Following Cohen’s guidelines [75], the analysis revealed that our design was sufficiently powered to detect small framing effects (f2 > 0.01) across the sample as whole, small to medium effects among the Alarmed, Concerned and Doubtful segments (f2 > 0.04, f2 > 0.02 and f2 > 0.06 respectively) and large effects among Disengaged and Dismissive groups (f2 > 0.45 and f2 > 0.12 respectively). A recent meta-analysis [66] reporting on 237 framing effects Table 3. Summary of experimental treatments and question wording. Options for revenue use and messaging Price 2 cents/litre (low) 11 cents/litre (high) No message (1) At 10$ per tonne, this policy will increase the price of fossil fuels, adding about 2 cents per litre at the pump. (2) At 50$ per tonne, this policy will increase the price of fossil fuels, adding about 11 cents per litre at the pump. Invest in solutions

(3) At 10$ per tonne, this policy will increase the price of fossil fuels, adding about 2 cents per litre at the pump. For each dollar increase it receives from this policy, the government will invest 1 dollar in solutions to address climate change: such as in clean energy, transit, and energy efficiency. (4) At 50$ per tonne, this policy will increase the price of fossil fuels, adding about 11 cents per litre at the pump. For each dollar increase it receives from this policy, the government will invest 1 dollar in solutions to address climate change: such as in clean energy, transit, and energy efficiency. Equal dividend (5) At 10$ per tonne, this policy will increase the price of fossil fuels, adding about 2 cents per litre at the pump. The atmosphere belongs to everyone, and a carbon price gives a signal to everybody–business and households–to reduce their carbon pollution. The government plans to equally distribute all of the revenue in the form of equal per capita dividends for every citizen. (6) At 50$ per tonne, this policy will increase the price of fossil fuels, adding about 11 cents per litre at the pump. The atmosphere belongs to everyone, and a carbon price gives a signal to everybody–business and households–to reduce their carbon pollution. The government plans to equally distribute all of the revenue in the form of equal per capita dividends for every citizen. Relative price (7) At 10$ per tonne, this policy will increase the price of fossil fuels, adding about 2 cents per litre at the pump. Although a

carbon price makes polluting more expensive, it also makes things like clean energy and electric vehicles more affordable. (8) At 50$ per tonne, this policy will increase the price of fossil fuels, adding about 11 cents per litre at the pump. Although a carbon price makes polluting more expensive, it also makes things like clean energy and electric vehicles more affordable. https://doi.org/10.1371/journal.pone.0273977.t003 PLOS ONE The Five Canadas of Climate Change PLOS ONE | https://doi.org/10.1371/journal.pone.0273977 November 23, 2022 8 / 21