Public understanding of climate change-related sea-level rise

more recent studies [25–27] than did AR5, assessed likely global sea-level rise by 2100 as rang- ing from 0.29 m to 1.10 m under the different IPCC scenarios. In the same report, thermal expansion, melting of the Greenland ice sheet, and melting of land-based glaciers were identi- fied as the main contributors to sea-level rise to date, with greater contributions from melting of the Antarctic ice sheets for the rest of the century and beyond [10]. To understand the public’s knowledge about the amount, rate and causal mechanisms of sea-level rise, we commissioned a national survey. To reflect the New Zealand population, sur- vey responses were weighted by age, sex, highest education, ethnicity and region using census data. The percentage results shown below are thus weighted to be representive of the New Zea- land population. Method Data were collected from a representative sample of 1100 New Zealanders aged 18 and over conducted by Horizon Research in September 2019. Participants, who were part of the com- pany’s research panel, completed 15 multichoice questions plus demographic questions online in their own time. In the information provided at the start of the survey, participants were advised that by continuing the survey they were giving consent for their responses to be used in this research, and were assured that it was an anonymous survey and they would not be identifiable. The research was approved by the Human Ethics Committee at Victoria Univer- sity of Wellington in August 2019 (reference number 0000027157).

The majority of respondents were male (50.5%), within the 45–54 years age bracket (22.7%), with a household income between $70,001 and $100,000 per year (17.9%), employed (69.5%), and indicated a personal income between $30,001 and $50,000 per year (19.6%), an undergraduate (Bachelor) degree as the highest qualification (29.1%), Auckland Council as their local government (32.8%), and NZ European/Pakeha as their self-identified ethnicity (64.2%). Prior to the representative survey, a pilot online survey, comprising 27 multi-choice and short answer questions plus demographic questions, was conducted in July 2019 and received 665 respondents, with respondents aged between 18 and 87, most of whom (58%) were female. The pilot survey was useful for informing the final representative survey and helping us to select the 15 most critical questions (scaling down the initial survey was necessary because of the financial constraints involved in using a company to collect data). We acknowledge Aker- lof’s points that “some fraction of the public has no prior opinion on questions asked in sur- veys, but feels impelled to provide an answer” [23, p. 423] and that “reported beliefs and attitudes may either be randomly chosen by the respondent or selected based on cues from the question format” [23, p. 423]. We excluded ‘I don’t know’ answers in many of the response options, though, because we wanted participants to indicate their view, or best approximate, even if they didn’t have full knowledge of the topic, and also because ‘I don’t know’ response

options can yield unwanted methodological issues [28]. The S1 File provides more detail about survey design and findings from other questions included in the survey (S1 File–representative and pilot surveys). The full survey, raw data, as well as overall descriptive results produced by Horizon Research, can be obtained in the Open Science Framework: https://osf.io/vcjuf/. Public overestimates sea-level rise possible by 2100 We first examined New Zealanders’ understanding of current sea-level rise. As noted, average global sea level has risen by more than 16 cm since 1900 [1]. Respondents were thus asked to identify, from options ranging from ‘not at all’ to ‘more than 40 cm’, how much they thought PLOS ONE Public understanding of climate change-related sea-level rise PLOS ONE | https://doi.org/10.1371/journal.pone.0254348 July 9, 2021 3 / 12