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Impacts: Rising sea levels

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Rising sea levels

 

Summary

  • Sea levels change relative to the land for many reasons, see Tab 1. What causes sea levels to change? 
  • The 2021 IPCC Sixth Assessment Report (AR6) projected that by 2100 global sea levels will rise at least 0.38m and as much as 0.88m relative to 1995-2014 levels (Tab 2|Fig. 2). Adding that: ‘a 2m sea-level rise by 2100 cannot be ruled out due to potential rapid ice-sheet instabilities’.

…multiple lines of evidence show that +1.5°C is too high and that even current climate forcing (+1.2°C), if sustained, is likely to generate several metres of sea-level rise over the coming centuries, causing extensive loss and damage to coastal populations and challenging the implementation of adaptation measures. To avoid this requires a global mean temperature that is cooler than present. – Stokes et al 2025

A SLR of 0.3 m – projected to occur by the second half of this century – would mean that high water levels, currently only experienced once in 100 years, would happen every year in Christchurch. For 0.7 m of rise, current 1-in-100 year levels would occur daily in some locations. – p22 NCCRA 2026 Climate Change Commission

  • The impacts will differ from coast to coast due to processes summarised in Tab 5: What are the effects of rising sea levels?

A common response to increasing climate risk is to “harden the coasts” to defend property from inundation. However, engineering solutions like seawalls, stopbanks, and levees only delay damage at best and might even be counterproductive, as it encourages intensification in hazardous locations. Responses to sea level rise insurance retreat should attempt to eliminate the underlying risk by moving homes out of harm’s way. – Storey et al 2020

  Impacts

Home > Climate wiki > Impacts > Rising sea levels

 

Summary

  • Sea levels change relative to the land for many reasons, see Tab 1. What causes sea levels to change? 
  • The 2021 IPCC Sixth Assessment Report (AR6) projected that by 2100 global sea levels will rise at least 0.38m and as much as 0.88m relative to 1995-2014 levels (Tab 2|Fig. 2). Adding that: ‘a 2m sea-level rise by 2100 cannot be ruled out due to potential rapid ice-sheet instabilities’.

…multiple lines of evidence show that +1.5°C is too high and that even current climate forcing (+1.2°C), if sustained, is likely to generate several metres of sea-level rise over the coming centuries, causing extensive loss and damage to coastal populations and challenging the implementation of adaptation measures. To avoid this requires a global mean temperature that is cooler than present. – Stokes et al 2025

A SLR of 0.3 m – projected to occur by the second half of this century – would mean that high water levels, currently only experienced once in 100 years, would happen every year in Christchurch. For 0.7 m of rise, current 1-in-100 year levels would occur daily in some locations. – p22 NCCRA 2026 Climate Change Commission

  • The impacts will differ from coast to coast due to processes summarised in Tab 5: What are the effects of rising sea levels?

A common response to increasing climate risk is to “harden the coasts” to defend property from inundation. However, engineering solutions like seawalls, stopbanks, and levees only delay damage at best and might even be counterproductive, as it encourages intensification in hazardous locations. Responses to sea level rise insurance retreat should attempt to eliminate the underlying risk by moving homes out of harm’s way. – Storey et al 2020

 Sea levels are constantly changing, and the effects are not the same everywhere

..actual sea-surface height is not just determined by the gravity and rotation of Earth, but also by, for example, ocean currents and large-scale circulation, winds, tides, seawater temperature and salinity. – Seeger & Minderhoud 2026

Sea level is generally referred to as ‘mean sea level’ or ‘MSL’ because the height of the ocean relative to the land is constantly changing for reasons summarised in Tab 1: What causes sea levels to change? Understanding vertical land movements (VLM) where the land is rising or falling relative to the ocean is a crucial factor for understanding how some coasts will be impacted sooner than others. This is refereed to as ‘relative sea-level rise’ (RSLR), that is, SLR+VLM. The NZ SeaRise tool (Tab 4) includes VLM to determine RSLR around Aoteaora. Earthquakes have also altered some coastlines in recent years. Understanding the variables of SLR is essential before making decisions about managing and living on coastal environments.

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