Public understanding of climate change-related sea-level rise

global sea level has risen since 1900. More than a quarter of respondents answered ‘10–20 cm’ (26.9%), a figure that is in line with current understanding of sea-level rise to date. But a larger proportion (38.2%) of respondents either underestimated the amount of sea-level rise, selecting ‘not at all’ (11.2%) or ‘5–10 cm’ (27%), or overestimated (35%) the amount of sea-level rise from 1900 to date, selecting ‘20–30 cm’ (13.4%), ‘30–40 cm’ (8.4%) or ‘more than 40 cm’ (13.2%). We then examined knowledge of sea-level rise projections to 2100 (see Fig 1A). While a minority (6.8%) of respondents said that sea level was not projected to rise by 2100, nearly 75% of respondents selected options that were in line with scientifically-plausible projections, selecting ‘up to 40 cm’ (28.6%), ‘up to 1 m’ (30.9%), and ‘up to 2 m’ (14.9%). But a large group of respondents (18.9%) overestimated sea-level rise projections to 2100, selecting ‘up to 5 m’ (10.7%) or ‘more than 5 m’ (8.2%). To further explore the amount of sea-level rise respondents thought was possible by 2100, we asked how much global sea level could rise by 2100 under ‘a scientifically credible worst- case scenario’ (see Fig 1B). While a similar small number of respondents said that sea-level rise was not going to happen at all (7%), and 22.5% of respondents underestimated the worst-case scenario by selecting ‘up to 1 metre’, this time only 33.1% of respondents gave an answer broadly in line with current science, answering ‘1 m or more’ (16.7%) or ‘2 m or more’

(16.4%). Another 37.4% of respondents substantially overestimated sea-level rise by 2100, selecting ‘5 m or more’ (18%), ‘8 m or more’ (7.3%), ‘12 m or more’ (5.3%) or ‘15 m or more’ (6.8%). To assess what respondents thought was physically possible, we then asked what they thought would be the ‘maximum amount of sea-level rise’ that could occur if ‘all of the glaciers Fig 1. Sea-level rise projections to 2100. (a): Respondents were asked ‘How much do you think global sea level is projected to rise by 2100?’ (b): Respondents were asked ‘How much could global average sea level rise under ‘a scientifically credible worst-case scenario’?. https://doi.org/10.1371/journal.pone.0254348.g001 PLOS ONE Public understanding of climate change-related sea-level rise PLOS ONE | https://doi.org/10.1371/journal.pone.0254348 July 9, 2021 4 / 12