3.1.3.3 - Climate, time and coastal landscape change

Observed change and coastal impacts

Climate influences coastal processes through sea level, weather, water and ecosystems, but a local change may have several causes.

IPCC AR6 (2021) reports global mean sea-level rise of 0.20 m, with an assessed very likely range of 0.15–0.25 m, between 1901 and 2018. Ocean thermal expansion and loss of land ice contribute to the rise. This is a global ocean measure over that period, not the relative level or flood depth at one beach. Land movement and regional ocean conditions modify local experience.

A higher baseline water level can allow waves to reach defences and cliff feet more often, increase overtopping and compound storm-surge flooding. A storm surge is a temporary departure of sea level from the predicted tide associated with weather, including wind and pressure. A high astronomical tide, surge and large waves can combine; their consequences also depend on beach width, barriers, drainage and exposure of people and property.

Rainfall changes can affect saturation and slope failure; drought can alter vegetation or sediment supply. Do not infer a uniform global increase in every coast's storm frequency from sea-level rise alone. To attribute a measured retreat event, check geology, rainfall, waves, water levels, sediment supply and interventions. A storm eroding a weakened cliff is evidence of a mechanism; it is not by itself a measurement of the climate-change contribution.

For example, ERYC's 2025–2026 cliff losses at adjacent Holderness profiles differ. Those observations demonstrate local variability during the reported intervals. They do not isolate climate forcing, because cliff condition, exposure and defences also differ.

Projections and conditional risk

A projection describes a possible future conditional on assumptions, with a range that must remain attached to its scenario and baseline.

For 2100 relative to 1995–2014, IPCC AR6 gives likely global mean sea-level ranges of 0.28–0.55 m under SSP1-1.9 and 0.63–1.01 m under SSP5-8.5. These represent different emissions pathways. They are not two observations, a local flood-depth forecast, or a guarantee that every location stays within the global range. Local relative projections, extreme-water levels and topographic evidence are required for a frontage decision.

Rising water can increase erosion/flood pressure, shift estuary salinity and change wetland inundation. A barrier or dune may migrate landward where sediment and space allow; a marsh may accrete or migrate. Fixed infrastructure can block that adjustment and produce coastal squeeze. Dredging, nourishment, adaptation and development also change future exposure, so vulnerability is not a purely physical number.