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

and Doubtful segments, but not among the Disengaged and Dismissive. Given this, we focus on the Alarmed, Concerned and Doubtful when looking at between-segment differences in message responses. Causal effects between experimental conditions were assessed using OLS regressions on our dependent variable. To make interpretation more straightforward, we also estimated the marginal effects of each treatment on attitudes toward carbon taxes. We began by examining how the level of policy stringency affected attitudes toward carbon taxes and whether the Five Canadas of Climate Change moderate this effect. First, we considered the effect of an 11-cent price increase on attitudes toward carbon taxes (as compared to 2 cents). As shown in the S1 File (Model 1 of S3 Table in S1 File), the effect of policy stringency was very small (0.001) and non-significant. Next, we included the Five Canadas of Climate Change in our model and examined the extent to which audience segments helped predict overall attitudes. As model 2 of S3 Table in S1 File demonstrates, the Five Canadas were significant predictors of attitudes toward the policy, with positive coefficients indicating that the model predicted more support- ive attitudes in each given group as compared to the reference category (i.e., the Dismissive). Belonging to the Doubtful increased the level of supportive attitudes by about 18% compared to the Dismissive segment, while belonging to the Alarmed increased the level of supportive attitudes by 42% relative to the Dismissive. In comparison, moving from the far right to the far

left on the ideological scale had a 14-percentage point effect on our dependent variable. The effect of the Five Canadas of Climate Change on attitudes toward carbon taxes is thus three times greater than that of political ideology. Adding the Five Canadas to the base model signifi- cantly improved model fit, with an adjusted r-squared increasing from 0.12 in the base model to 0.30 in the fully specified model, F (4, 922) = 64.10, p < 0.001. To test the potential of policy stringency to affect audiences in different ways, we added interaction terms, multiplying segments by price levels (Model 3 of S3 Table in S1 File). Inter- action terms between segments and price levels were very close to zero and failed to reach sta- tistical significance, suggesting that moving stringency from a low (2 cents) to a relatively higher (11 cents) increase in the gasoline price at the pump left attitudes unchanged across segments. Table 4. Mean level of attitudes toward carbon taxes, by audience segment and experimental treatment (mean/standard deviation, N in parentheses). National average Alarmed Concerned Disengaged Doubtful Dismissive 2 cents/litre (low) No message .48/.25 .64/.19 .52/.19 .40/.35 .30/.21 .16/.22 (131) (34) (58) (4) (21) (14) Equal dividend .46/.27 .65/.24 .51/.20 .49/.33 .33/.22 .05/.07 (133) (32) (57) (6) (26) (12) Invest in solutions .44/.28 .56/.27 .52/.22 .27/.18 .32/.26 .09/.11 (137) (37) (53) (5) (31) (11) Relative price .48/.25 .59/.25 .52/.22 .60/.13 .37/.23 .12/.2 (131) (36) (58) (3) (26) (8)

11 cents/litre (high) No message .42/.27 .56/.27 .44/.26 . .32/.22 .15/.2 (141) (29) (72) (0) (28) (12) Equal dividend .46/.27 .57/.22 .53/.23 .33 /.30 .39/.27 .21/.25 (137) (22) (68) (7) (24) (16) Invest in solutions .48/.27 .55/.22 .58/.23 .57/.08 .23/.16 .09/.11 (138) (36) (69) (2) (20) (11) Relative price .53/.24 .66/.19 .54/.19 .39/.39 .45/.21 .09/.23 (136) (36) (79) (2) (19) (9) https://doi.org/10.1371/journal.pone.0273977.t004 PLOS ONE The Five Canadas of Climate Change PLOS ONE | https://doi.org/10.1371/journal.pone.0273977 November 23, 2022 11 / 21