Study 1: From the Lab to the Field

We first conducted a large-scale field experiment to estimate how a conservative organization’s messages affected right-leaning Americans’ support for climate action. This organization drew on survey-experimental findings in the climate communication literature to develop a large-scale direct mail campaign tailored to a conservative audience. We know of no prior published research that has used individual-level randomization or a within-subjects design to measure the real-world impacts of a large-scale climate messaging campaign.

For this study, we partnered with republicEn, a non-profit organization that promotes conservative solutions to climate change. The organization was ideal because it is a conservative group headed by a former Republican member of Congress, Representative Bob Inglis from South Carolina. Moreover, Inglis’s own messaging strategy has previously performed well in survey experiments. The successful Goldberg et al. (Reference Goldberg, Gustafson, Rosenthal and Leiserowitz2021) field experiment used messages developed by Inglis, and in another survey experiment analyzing recorded messages from a dozen climate activists, Inglis’s recording had the largest impact (Commercon et al. Reference Commercon, Goldberg, Rosenthal and Leiserowitz2021).

In late spring 2022, republicEn worked with experts in political marketing to develop four postcards rooted in climate messaging strategies supported by past survey-experimental research:

1. (a) Shared conservative identity emphasized how shared conservative values support action on climate change,

2. (b) Adversarial conservative identity emphasized shared conservative values and a concern that the political left would ‘get it wrong’ on climate change,

3. (c) Scientific consensus emphasized that 97 per cent of scientists agree that climate change is happening and human-caused, and

4. (d) Health effects emphasized the negative health effects associated with climate change.

Each of the four main postcards used different images, fonts, and text. To separate the effects of formatting from message effects, republicEn also developed three variants of the shared conservative identity, scientific consensus, and health effects postcards that mirrored the fonts, images, and colours from the adversarial conservative identity postcard. To separate message effects from messenger effects, they also developed two variants of the scientific consensus and health effects postcards that removed any reference to shared conservative values and changed the institutional affiliation of the sender from republicEn to the George Mason Energy and Enterprise Initiative. (For postcard images, see Appendix A.)

We then sent lettersFootnote ³ to 62,885 Republican voters in a conservative Southern US congressional district inviting recipients to participate in an ostensibly unrelated online survey; 4,222 people did so. A month after our survey invitation, republicEn sent postcards to people who opted to participate in our survey, following the Broockman, Kalla and Sekhon (Reference Broockman, Kalla and Sekhon2017) framework for individual-level field experiments with survey outcomes. Each participant was randomly assigned one of the nine postcard designs (sending the same card three times within one week, per the advice of republicEn’s advertising firm) or to a control group that received no postcard. A few days after the last postcard, we sent an ostensibly unrelated survey to determine how recipients’ attitudes had changed; 2,353 completed the second-wave survey (56 per cent, an acceptable response rate by the standards of similar studies; Broockman, Kalla and Sekhon Reference Broockman, Kalla and Sekhon2017). (For additional technical details about each of our experiments, see Appendix C.) Using data from republicEn, we also studied the rates at which respondents engaged in the actions republicEn hoped to elicit: following the QR code link on the postcard to watch climate-related videos and signing up for the organization’s email list.

We expected voters who received these postcards to be more likely to report four of the beliefs that have been most often studied in the literature on climate communication; namely, the views that climate change is (1) happening, (2) human-caused, (3) concerning, and (4) the most important problem facing the country. In Study 1, we also tested the hypotheses that recipients would be more likely to think that climate change was (5) concerning to other Republicans (for question wording, see Appendix C) and that they would be (6) more likely to engage with republicEn (by signing up for the organization’s email list).Footnote ⁴

However, none of the hypothesized effects were clearly supported by the results of the study. We first analyzed data from republicEn on engagement. Each postcard invited recipients to help republicEn by using a QR code, which directed users to a website where they could rate three videos on climate change. The partner organization supplied us with data on QR code use and whether research subjects took the low-stakes but significant step of signing up to receive emails from republicEn (thereby becoming members of the organization). Of the 4,222 people who completed the first-wave survey, 3,797 received one of the nine versions of the postcard (425 were in the control group). However, in the two weeks after the first postcard arrived, the QR codes on the postcards were used to access the republicEn landing page just ninety-six times (at most, 2.5 per cent of recipients, assuming that no recipient visited the site more than once), and only 14 of the 3,797 postcard recipients signed up for the republicEn listserv (0.4 per cent), a difference relative to the control group that was not statistically significant even at p < 0.20. That is, registrations for republicEn’s email list were so few that, in a statistical sense, we could not reject the hypothesis that the postcards failed to cause anyone to sign up for republicEn (although, obviously, fourteen participants did in fact sign up).

Of course, postcards that fail to move people to action might still nudge them to update their views. However, comparing first- and second-wave surveys did not suggest that meaningful attitude change occurred. Figure 1 graphs the average effect of each postcard (relative to the control group) on each of the six survey items (Happening is shaded black, Human-caused is shaded dark grey, and so on). To facilitate comparison, we rescaled each survey item to range between 0 and 1, so the effects in the figure represent the percentage of the maximum effect a postcard could have had. All of the estimates were calculated so that higher values were in line with our expectations —for example, higher values in the graph indicate that the average participant was more likely to believe that climate change is happening, human-caused, or concerning after receiving the postcard. (Complete regression model results are listed in Appendix Table A1.)

Figure 1. Postcards Had Little Consistent Effect on Recipient Attitudes.

Notes: Each outcome variable is rescaled to range between zero and one. N= 2,353. Regression models are listed in Appendix Table A1.

For the vast majority of postcards and survey measures, there were no effects: the estimated associations were small (usually around 2 percentage points on the average participant’s score on that measure) and not statistically significant. There were just five combinations of survey measures and postcard types that generated statistically significant differences (we would expect three by chance alone), and no clear patterns were evident that would indicate that one postcard performed better than the others. The estimated differences associated with all nine postcards (the bottom group of bars in the graph) were around 2 percentage points on most survey items and were not statistically significant. In other words, the average postcard did not have an effect, and there was no ‘standout’ postcard that consistently performed well. Most estimates were positive —on most of our six survey measures, the average participant was slightly (but not significantly) more likely to give the expected response. Overall, however, a professionally designed postcard campaign rooted in extant survey-experimental findings and fielded by a conservative organization with a track record of success in past survey experiments ultimately had little short-term impact in this real-world direct mail campaign.Footnote ⁵

Study 2: Back to the Lab Again

Could attention be the problem with the postcards in Study 1? To find out, we conducted a survey experiment to determine whether our non-findings in the first study were because the messages themselves were unpersuasive or perhaps because recipients simply did not pay attention to the postcards. To facilitate comparisons, we used the four main postcards from Study 1 and made only minor revisions to our survey questions about climate attitudes. In effect, we asked whether we could use the same materials but experimentally manipulate attention to generate the non-findings in our field experiment and the positive findings common in survey experiments.

Using the Cint online platform, we sent a survey to 1,982 self-identified Republicans across the USA in December 2022 and January 2023. At the outset, we randomly assigned each respondent to either a control group, a low-attention group, a medium-attention group, or a high-attention group. The control group was not shown a republicEn postcard but still answered all the core survey questions, including about their climate views. The low-attention group was shown one of the four main republicEn postcards (randomizing which card) and answered an additional question about whether they had received a similar political mailer in the past; this item simulated a real-world setting in which people are free to briefly glance at postcards and move on. The medium- and high-attention groups were shown one of the four postcards and forced to remain on that screen for a full minute, then asked two factual questions about the postcard’s topic (climate change) and messenger (republicEn.org). The high-attention group was also asked whether the postcard was persuasive and to write a brief open-ended evaluation of it.Footnote ⁶ Survey experiments might generate larger effects than field experiments because they require participants to receive the message in question, which induces attention to the messages and/or causes inattentive people to drop out of the study at higher rates (by asking them to do something they do not wish to do —pause and pay attention to the study materials —or screens them out with pre- or post-manipulation attention checks), leaving behind only more attentive people who have received the message.

Figure 2 plots the effects of viewing a postcard; as in Figure 1, the outcome variables are scaled to range between zero and one. The topmost group of four bars compares the participants in the low-attention condition (who had the option to view the postcard only momentarily) to the control group (who did not view any postcards). The second group of bars compare the control group to respondents in the medium-attention group (who were required to view the postcard for one minute and answer two factual questions about it) and the bottom group of bars compares the control group to the high-attention group (who were required to view the postcard for a full minute, answer two factual questions, and then answer two evaluation questions).

Figure 2. Attention Was a Key Mediator in Postcard Effects.

Notes: Each outcome variable is rescaled to range between zero and one. Control group n = 441. Regression model results are listed in Appendix Table A2.

In line with the results of Study 1, respondents in the low-attention group were 3 to 5 percentage points more likely to report that they believed that climate change was happening, human-caused, and concerning, and the differences were not statistically significant. That is, respondents who were free to ignore the message did not exhibit measurable short-term changes in their climate attitudes. However, when respondents were forced to view the postcards for just one minute, they exhibited statistically significant differences in their climate attitudes, more in line with past survey-experimental research. Respondents in the medium-attention condition who were required to view the postcards for one minute were 7 to 14 percentage points more likely to say that climate change is happening, human-caused, and concerning (relative to people in the control group who did not see postcards), and the differences were statistically significant. Respondents in the high-attention group were 5 to 7 percentage points more likely to report that climate change was happening and concerning, and the differences were statistically significant (except on the item about whether climate change is human-caused).

Our findings were similar in robustness tests that added controls, estimated two-stage models using attention check questions, separately compared participants who were and were not primary election voters, and analyzed the four postcard designs separately (see Appendix C). We found little evidence of differential attrition in this context (see footnote 6); we believe the differences noted here reflect differences in induced attention. When we allowed people to ignore the postcards (in a setting that mimicked the real world of large-scale messaging campaigns), our findings mimicked the null results of the field experiment in Study 1. When we compelled respondents to pay attention to the postcards (in a setting that mimicked recent successful survey experiments), our findings mimicked the encouraging results of recent successful survey experiments. Attention, then, would seem to be one key to understanding why climate messages that work in the lab do not necessarily generate large effects in the field.

Study 3: Can Direct Mail Induce Attention?

If attention is a key obstacle to translating messages developed in the lab into a direct mail campaign, can activists simply generate more attention in the field? To test one way to do so, we worked with republicEn to conduct a third experiment. In December 2023, republicEn selected a congressional district for a direct mail campaign, and in January 2024 we sent emails (rather than letters, as in Study 1) inviting 50,000 registered Republicans in that district to participate in an ostensibly unrelated survey; 538 completed the initial survey (a far lower response rate than in Study 1, likely owing to our switch from mailing physical invitations in Study 1 to emailing survey invites in Study 3).

In February 2024, republicEn sent each of our 538 survey participants one of two postcards (there was no control group): the Scientific Consensus postcard from Study 1 or a modified version designed to be more attention-grabbing (for an image, see Appendix C). Instead of opening with ‘More than 97 per cent of climate scientists have concluded …,’ the alterative postcard began ‘What % of Climate Scientists agree, based on evidence, that humans are causing climate changes?’ then featured three brightly-coloured scratch-off panels with the numbers 38 per cent, 63 per cent, and 97 per cent printed on them. If participants scratched off either of the lower numbers, they revealed text that read ‘Higher!’ A few days after the last postcard arrived, we sent a second wave of ostensibly-unrelated surveys, offering a $5 Amazon gift card to those who completed them; 308 participants did so (a 57 per cent re-interview rate, similar to Study 1).Footnote ⁷

However, we found no differences in effects between the original and more attention-grabbing postcards. Relative to participants who received the standard postcard, those who received the scratch-off were about half a percentage point less likely to say that climate change was happening, 6 percentage points more likely to say that it was human-caused, 1 percentage point higher on the Six-Americas concern scale, and half a percentage point less likely to say that they were concerned about climate change on the Pew scale (the first four measures in Figure 1). None of the differences were statistically significant. No respondent in the post-survey indicated that climate change was one of the most important problems facing the country (the fifth measure in Figure 1). (Regression results are listed in Table A7.) Attention seems to be a key obstacle to translating lab-based climate messages into large-scale campaigns —and overcoming that obstacle (at least in the context of a direct mail campaign) is no small task.

Attention, Climate Messaging, and the Lab-to-Field Disconnect

Our findings suggest that the climate messages tested in survey- and lab-based experiments may be difficult for advocates to effectively use in a real-world setting. Moreover, our findings highlight one reason why: attention. As Study 1 shows, lab-tested messages do not translate readily into a standard direct mail campaign. However, as Study 2 shows, attention seems to be a key driver; people who are forced to pay attention exhibit large effects, while those who are free to quickly move past them (like people in the real world) do not. Unfortunately, getting people’s attention is challenging in practice, as Study 3 shows. If the first step in political attitude formation and change is that people must receive a message (Zaller Reference Zaller1992) —that is, must actually notice it —attention should be front-and-centre in academic and practitioner conversations about lab- and survey-based messaging interventions.

Lab and survey experiments can identify effective messages, but if activists and practitioners wish to put those messages to work, they must overcome the messy realities of real-world political persuasion, including the simple fact that it is hard to get people to pay attention to messages they don’t want to receive (a challenge that is well-known to advertisers, politicians, and scholars of persuasion). In that sense, this study joins a growing body of academic research that finds that large-scale political messaging campaigns usually do not work (Cardy Reference Cardy2005; Bailey, Hopkins and Rogers Reference Bailey, Hopkins and Rogers2016; for a meta-analysis of forty-nine field experiments, see Kalla and Broockman Reference Kalla and Broockman2018) and that political persuasion is generally challenging (for example, Cohen, Aaronson and Steele Reference Cohen, Aaronson and Steele2000; Iyengar and Hahn Reference Iyengar and Hahn2009; Sigelman and Sigelman Reference Sigelman and Sigelman1984; Zaller Reference Zaller1992; McCright et al. Reference McCright, Charters, Dentzman and Dietz2016).

Of course, caveats abound. We focus here on direct mail, but many other media are suitable for large-scale political marketing (although canvassing and phone banks seem to perform little better; see Kalla and Broockman Reference Kalla and Broockman2018). More intense multi-media campaigns might be more effective (Goldberg et al. Reference Goldberg, Gustafson, Rosenthal and Leiserowitz2021 used a multi-platform online messaging strategy over the course of a month); so might well-designed door-to-door campaigns (for example, Broockman and Kalla Reference Broockman and Kalla2016). Moreover, researchers and activists may be able to devise more attention-grabbing direct mail materials than we have studied here, though this possibility seems unlikely to us, given that our partner organization tried ten different postcard designs in all. Our point is not that direct-mail or other large-scale messaging campaigns cannot be effective; it is that they are not nearly as effective as what we might expect based on a naïve reading of the optimistic results of recent survey experiments on climate communication. Large-scale messaging campaigns about climate —or any other topic —need to be sensitive to the reality that attention is easy to generate in a lab or survey and hard to generate in the real world.

We would also note that this study uses three different experiments with slightly different approaches and samples. This is partly by design; to understand differences between lab- and survey-based experiments, Studies 1 and 3 use the within-subjects approach often used in field experiments, and Study 2 uses the between-subjects design that is more common in lab- and survey-based studies. By necessity, moreover, the populations we sampled from could not be identical in each study: Study 3 could not be carried out using the same population as Study 1 (because repeating the experiment in the same state would undoubtedly alter the findings), and Study 2 was conducted using an online survey panel. We have done our best in all three cases to identify relevant participants —Republicans —but of course these differences in samples and experimental designs create some risks relative to studies that can be carried out using essentially identical participant populations and experimental frameworks.

Another word of caution we would add is that this study has focused on the role of attention, but not other obstacles in lab-to-field messaging, including the problem of durability. Direct mail and other mass-media campaigns fight an uphill battle to win the attention of targeted recipients; they fight yet another to durably change opinions (Broockman and Kalla Reference Broockman and Kalla2016). Our experiments suggest that a well-designed postcard campaign did not move attitudes in the short term; moving them in the long term would surely pose further difficulties.

Of course, researchers and practitioners who care about climate change —or any issue, party, or candidate —should continue developing persuasive messages in survey- and lab-based experiments. But there is still a great deal of work to be done to ensure that real-world messaging campaigns actually get people’s attention —and ultimately persuade them.