Public understanding of climate change-related sea-level rise

adopted the baseline used in reports by the IPCC [11] and the New Zealand Ministry for the Environment [12]. Projections in these reports are relative to mean sea level averaged over the two-decade period 1986–2005.) Moreover, present day extreme water-level events will become commonplace within the next few decades [9] and sea-level rise of 0.39 m (0.26–0.53) by 2100 is likely even under the lowest emissions pathway (RCP2.6) [1]. While mitigation efforts are still important, adaptation to this coastal change is essential and urgent, and will require signif- icant financial investments [9, 13]. Support from publics–as voters, taxpayers, coastal resi- dents, and coastal business owners–is thus essential. This paper uses New Zealand as a case study to gauge the public’s current understandings of sea-level rise. New Zealand is an island nation in the South Pacific, stretching 1,500 km between latitudes 34˚ and 47˚ south. The country has 18,000 km of coastline with no point on land more than 130 km from the sea [14], and it has a population of five million people [15], most of whom live in coastal cities or districts. Most New Zealanders believe climate change is occurring, is anthropogenic, and is a serious concern [3, 16]. Notably, stories about sea-level rise in the mainstream news media are largely consistent with the scientific consensus and reports issued by the Intergovernmental Panel on Climate Change (IPCC) [17]. In a 2015 report, the New Zealand Parliamentary Commissioner for the Environment

noted, “It is certain that the sea is rising and will continue to do so for centuries to come. But much is uncertain–how rapidly it will rise, how different coastal areas will be affected, and how we should prepare” [18, p5]. The NZ SeaRise Programme aims to address this uncertainty with a 5-year (2018–2023) government-funded research initiative [19]. Its goal is to produce a set of location specific sea-level rise projections for New Zealand’s coastline, taking into account global and regional sea-level rise projections and new knowledge of local vertical land movements. This study is part of the public engagement workstream of the NZ SeaRise Programme. Too often, development of outreach activities is dominated by intuitive approaches and per- sonal or institutional motivations [20]. Relevant literature, though, advises that designing a public engagement campaign involves first understanding your audience and determining what they already know [21, 22]. Survey data is one form of evidence that can be used to inform the design of public enagement programmes on sea-level rise [23]. To gauge current understanding of sea-level rise, we therefore conducted a pilot study followed by a representa- tive survey to identify what New Zealanders knew about the amount, rate and causal mecha- nisms of sea-level rise. The survey was initiated with an awareness that while media coverage in New Zealand tends to focus on IPCC projections and government reports, there is also voice given to climate change deniers and to people who warn of catastrophic sea-level rise

[17]. Results of the survey will inform NZ SeaRise Programme researchers who are planning, or undertaking, efforts to engage publics with the issue of sea-level rise. Rather than starting with assumptions about what publics know and understand, researchers can use the survey results to approximate the knowledge and perspectives of the publics they are seeking to engage with. Regarding the rate and timing of future sea-level rise, projections from the Fifth IPCC Assessment Report (AR5) put likely mean global sea-level rise by 2100 at between 0.26 to 0.98 m [11]. In 2017, the New Zealand Ministry for the Environment published projections for New Zealand of 0.46–1.05 m of sea-level rise by 2100, depending on how quickly global carbon emissions are reduced [12]. These projections did factor in a modest Antarctic ice melt contri- bution that was not assessed in the AR5; however, a subsequent study using a structured expert judgment approach that evaluated all the latest projections [24] found that global sea-level rise could exceed 2 m by 2100 under a low-probability, high-emissions scenario. The 2019 IPCC Special Report on the Oceans and Cryosphere in a Changing Climate [1], which reviewed PLOS ONE Public understanding of climate change-related sea-level rise PLOS ONE | https://doi.org/10.1371/journal.pone.0254348 July 9, 2021 2 / 12 data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.