Public understanding of climate change-related sea-level rise

mechanisms that do contribute to sea-level rise, selecting melting ice sheets (24%), thermal expansion of the oceans (7%), and melting of land-based glaciers (4.2%). When we grouped respondents’ top three rankings for causes of sea-level rise (Fig 2B), melting ice sheets (62.3%) was first, followed by melting sea ice (59.8%), melting of land-based glaciers (44.1%), thermal expansion of the oceans (23.6%) and land subsidence in some areas (14.2%). There were also large proportions of respondents ranking some other mechanisms that do not impact on sea-level rise, such as ‘increased slash and sediment runoff due to defor- estation’ (14.3% ranked it in their top three), ‘dumping of rubbish/waste into the ocean’ (14%), ‘increased rainfall in the tropics’ (9.9%) and ‘submarine landslides’ (7.5%). Notably, 25.9% of respondents also ranked ‘something else’ as one of the top three causes of sea-level rise. When asked to specify what these causes might be, more than half (54%) were unsure or gave no answer, while 23.5% attributed sea-level rise broadly to climate change, global warming or human activities, and 16.5% gave answers such as ‘solar activity’, ‘earth- quakes’, or ‘storms’, suggesting these respondents believe natural processes are responsible for sea-level rise. Challenges of projecting and communicating sea-level rise Projecting sea-level rise is complicated [32]. Different climate, mountain glacier and polar ice sheet models produce different results. This is especially the case for Antarctic ice sheet mod-

els, which can range from projecting a net gain in mass to a significant loss. Thus, the IPCC approach is to take the mean of ensembles of model experiments, that all use broadly similar boundary conditions and climate forcings. Moreover, glacier melting, vertical land movement, gravitational effects, and ocean dynamics all contribute to sea-level rise being different in dif- ferent locations; and calculations must be made for a number of different scenarios represent- ing different mitigation pathways [33]. Sea-level rise projections are therefore usually scenario dependent and framed in terms of a probablistic range, rather than a single figure, to reflect the uncertainty in the projections. Communicating about sea-level rise, given the uncertainties inherent in projections, is also complicated [8]. IPCC reports, which assess and interpret all the latest science, contain jargon and caveats about ‘uncertainty ranges’ with evidence that publics misunderstand verbal proba- bility expressions, known as calibrated uncertainty language [34], such as ‘likely’ and ‘unlikely’ [35]. Even the IPCC summaries for policymakers have been criticised for their formal struc- ture and use of jargon [36]. This is a complex challenge for science communicators. As noted by Seethhaler et al, communicating about uncertainty is “one of the greatest challenges in sci- ence communication, one that raises ethical issues including, but not constrained to, finding a middle ground in prognostication between false assurances and doomsday scenarios” [37, p. 381].

Media interpretations of the science adds to the problem. While the New Zealand media gives extensive coverage to IPCC projections, it also gives voice to more extreme and cata- strophic views from local and international scholars. For example, in 2016 New Zealand media reported on research that projected several metres of sea-level rise by 2100 [38–40], and in 2017 there was significant media coverage when a philosophy professor warned that sea-level rise could reach 5 m or more by 2100 [41–43]. These stories, though, also included comments from scientists who communicated the IPCC projections and from politicians who underesti- mated the importance of sea-level rise as an issue. Such indiscriminate media coverage, and attempts at journalistic balance, draw the uncertain nature of sea-level rise projections to the public’s attention and detract from the certainties that exist out to 2050. This could therefore be contributing to public confusion on the issue. While our pilot study revealed that the PLOS ONE Public understanding of climate change-related sea-level rise PLOS ONE | https://doi.org/10.1371/journal.pone.0254348 July 9, 2021 6 / 12