Sea Level Rise Myths: What the UK Evidence Actually Shows

Sea level rise is slow when measured against a human day and fast when measured against human history. Both things are true at once, and most myths live in the gap between them. The global average rise is a few millimetres a year, roughly the width of two grains of rice laid side by side (Woods Hole Oceanographic Institution). You cannot see that from a promenade. You can only see it in long, careful records: tide gauges running for more than a century, and satellites measuring the whole ocean since the early 1990s. That is why we think the most useful response to a myth is not ridicule. It is a better question.

This is the most widely shared myth in Britain right now. Reuters has fact checked a steady run of these comparisons, from Cornwall to the English coastline more broadly, and found the same problem each time (Reuters).

The grain of truth: a century of rise really is too small to see by eye in a photograph.

What it misses: the tide. A photo taken at an unknown point in the tidal cycle cannot show a change of 20 cm when the water moves several metres in a few hours. A National Oceanography Centre spokesperson made exactly this point about St Michael's Mount, where daily tidal variation far exceeds the UK's sea level change to date (Reuters).

Before trusting any "then and now" coastline image, it might be worth asking four quiet questions:

1. When in the tide was each photo taken? Without the date, time and local tide table, the comparison tells you almost nothing.

2. Which way is the land moving? Parts of Britain are rising and parts are sinking (more on that below).

3. What else has changed? Sea walls, rebuilt harbours, moved landmarks and new sand can all change how the water appears.

4. Is the image real? Increasingly, this needs checking first rather than last.

If a picture cannot pass those four questions, it is a mood, not a measurement.

This one has a scientific veneer, which makes it more persuasive than a meme. The grain of truth: sea levels were rising through the twentieth century, and some recent analyses of individual tide gauges have reported no significant acceleration at most stations. A 2025 paper by Voortman and de Vos made that argument. A comment from researchers at Cornell University, published online but not yet peer reviewed, argues that the result comes from a misread statistical correction and models too complicated for the data available; when simpler models or pooled data are used, they find a statistically significant acceleration (Cornell University).

What it misses: the weight of the wider record. The IPCC found that the global average rate of rise was 1.3 mm a year between 1901 and 1971, 1.9 mm a year between 1971 and 2006, and 3.7 mm a year between 2006 and 2018 (IPCC). Satellite records tell the same story: the rate nearly doubled from 2.1 mm a year in 1993 to 2002, to 4.1 mm a year in 2016 to 2025 (World Meteorological Organisation).

Closer to home, the Climate Change Committee reports that sea level at Newlyn in Cornwall is now rising at 4.6 mm a year, against a long term average of 2.1 mm a year since 1916 (Climate Change Committee). Individual gauges are noisy. Together, they point one way.

This myth comes in two versions, and both are slightly wrong.

The grain of truth: ice that already floats displaces its own weight in water, so the familiar ice cube in a glass barely changes the level when it melts.

What it misses: the main drivers sit elsewhere. Around two thirds of global sea level rise since the early 1990s comes from melting land ice, such as glaciers and the Greenland and Antarctic ice sheets, and the remaining third from seawater expanding as it warms (Woods Hole Oceanographic Institution).

Floating ice is not quite zero, though. Because sea ice and ice shelves are fresh water sitting in salty water, their melt takes up a little more space than the water they displaced. NASA estimates floating ice added about 1.1 mm to sea level between 1994 and 2017, roughly 3% of the effect of melting grounded ice (NASA). Small, but real. Much of climate science lives in that kind of detail.

The grain of truth: there is a global average, and it is a genuinely useful number.

What it misses: what matters on any given coast is relative sea level, meaning the sea's height compared with the land beside it. Britain is still settling after the last ice age. The weight of the ice pressed Scotland down, and as it rebounds, the whole island tilts gently: Scotland is rising and southern England is sinking, by up to about 1 mm a year (UK Government exploratory projections).

That tilt shows up clearly in the Met Office's projections for 2100. Under a low emissions pathway, sea level in London is projected to be 0.29 to 0.70 m higher than the 1981 to 2000 average, compared with 0.08 to 0.49 m in Edinburgh. Under high emissions, London's range rises to 0.53 to 1.15 m (Met Office).

The same sea, very different stories. For businesses and households on the south and east coasts, the national average quietly understates what is coming.There is also a newer twist. A 2026 study in Nature found that most coastal hazard assessments had assumed sea levels from mathematical models rather than actual measurements, and that measured coastal sea level was on average around 24 to 27 cm higher than those assumptions ( Seeger and Minderhoud, Nature). In other words, the starting line is higher than many maps suggest, especially in parts of Southeast Asia and the Pacific.

This is the myth we find most interesting, because the underlying science is genuinely surprising.

The grain of truth: a peer reviewed study of all 101 reef islands in Tuvalu found that total land area grew by 2.9% between 1971 and 2014, even as local sea level rose by about 3.9 mm a year. Seventy three islands grew (Kench et al., Nature Communications).

What it misses: the same study found that 28 islands shrank and one disappeared, with erosion concentrated on the smallest islands. The authors' conclusion was not that risk had vanished, but that reef islands are dynamic, so adaptation plans should reflect how they move and change (Kench et al., Nature Communications).

In CNB's view, there is a human distinction worth holding here. Sand can shift and rebuild. Homes, freshwater wells, roads and graveyards do not move with it. An island that keeps its area while its shoreline relocates is still asking a great deal of the people who live there.

The grain of truth: the largest changes are still ahead, and no one is suggesting British towns will disappear next year.

What it misses: sea level rise does its damage mostly by making ordinary events more dangerous. The last four years were the highest on record for UK annual mean sea level, and the National Oceanography Centre notes that if Storm Éowyn had arrived a week later in January 2025 and coincided with a spring tide, the water level at Heysham in Lancashire would have made it a one in 300 year event (National Oceanography Centre).

The Environment Agency expects that by 2100, extreme sea level events that currently occur once a century will occur annually (Environment Agency). Coastal erosion tells a similar story: around 3,500 properties in England are in areas at risk up to 2055 if current shoreline plans are delivered, rising to 19,700 by 2105 with climate change, and as many as 44,500 by 2055 if those plans are not delivered (Climate Change Committee).

Planning is already under way. In London, the Thames Estuary 2100 plan expects the Thames Barrier to close more and more often for ordinary high tides, with some upstream defences needing to be around 50 cm higher by 2050 (Environment Agency). Engineers do not plan concrete around a hoax.

The grain of truth: sea levels have moved dramatically over geological time, including a very large rise at the end of the last ice age.

What it misses: the recent past was remarkably stable. Evidence from salt marsh microfossils suggests sea levels stayed fairly constant, or rose only slightly, for at least 3,000 years before the Industrial Revolution (Woods Hole Oceanographic Institution). The European Environment Agency states that since 1970, human influence has been the predominant cause of accelerating sea level rise, both globally and in Europe's seas (European Environment Agency).

Natural change explains why the coast has a history. It does not explain why the pace has picked up in our lifetimes. For a wider look at how that scientific consensus was built, our guide to the climate studies that united scientists is a good companion read.

This is consistent with how we treat any emerging Scope 3 category. Certification means we can show the reader the basis for the claim, not that every corner of the value chain has been measured with laboratory precision. AI is a good example of why that matters. A defensible estimate today, improved each reporting year, is worth more than a confident silence.

Scrutiny of AI's carbon impact is going to sharpen over the next couple of years. That is a good thing. It is the same pressure test that has been applied to flights, supply chains and offset markets, and it will produce the same result: better data, clearer language, and businesses that can answer the follow-up question without hesitating.

This is the newest myth, and perhaps the most corrosive, because it sounds like realism.

The grain of truth: some rise is now committed. The IPCC is clear that sea level will keep rising for centuries because the deep ocean continues to warm and the ice sheets continue to lose mass, and it will stay elevated for thousands of years (IPCC).

What it misses: how much and how fast are still very much open. The IPCC's likely range for global rise by 2100 is 0.28 to 0.55 m under very low emissions, compared with 0.63 to 1.01 m under very high emissions (IPCC). The European Environment Agency adds that every five year delay in global emissions peaking increases median projected sea level rise by 2300 by around 0.2 m (European Environment Agency).

That is not a counsel of despair. It is the opposite. It means the choices made this decade shape the coastline our grandchildren inherit.

The table below draws on the sources cited in each section above.

Sea level rise may be the clearest illustration of something we say often: credible climate action has more than one job, and those jobs need to start together. Some rise is already committed by carbon that is already in the atmosphere and heat that is already in the ocean. That means coastal adaptation matters now: defences, shoreline planning, and honest conversations about where people live and build.

At the same time, the scale of future rise depends on the emissions still to come. Reducing those emissions as quickly and practically as possible changes the trajectory. And because cumulative emissions are what keep warming the ocean, high integrity carbon removals have a specific role in addressing carbon that is already up there. Avoidance and reduction projects play a different part, preventing emissions against a defined baseline.

None of this is an argument for waiting until one task is finished before beginning the next. Reduce, adapt and finance verified climate action, all at once, with scrutiny applied to each.

For British businesses, the practical starting point is usually a clear picture of their own emissions, which is what a carbon emissions report provides. From there, the question becomes how to reduce what can be reduced and support certified carbon offsetting projects with clear registry evidence, transparent documentation and an honest description of what each credit does. Some of the projects closest to this subject sit on the coast itself, which is why we have written about the potential of blue carbon ecosystems.

The sea will keep rising for a long time. How far it rises is still, in part, a matter of what we choose next.