Fact Check: Why Then-and-Now Harbour Photos Can't Disprove Sea-Level Rise

Visual comparisons of historic harbours often fail to account for tidal variations, creating misleading narratives about climate data.

Across social media platforms, a recurring genre of climate misinformation relies on a simple visual gimmick: placing a historical black-and-white photograph of a famous harbour or coastline next to a modern image of the exact same location. The accompanying text inevitably points out that the water level against the sea wall looks identical, suggesting that global sea-level rise is either a hoax or entirely trivial.

Recently, images of British harbours—such as Newlyn and Plymouth—have gone viral using this exact formula. However, scientific organizations, including Reuters Fact Check and NOAA, have repeatedly debunked this premise. Understanding why these photos are misleading requires a look into the complex science of tidal fluctuations and the precise instruments scientists actually use to measure our changing oceans.

Key Takeaways:

• Static photograph comparisons are scientifically invalid due to extreme daily tidal variations.
• Global mean sea levels are rising at an accelerating rate, currently estimated at 4.4 mm per year.
• Historic tide gauges, such as the one at Newlyn, show a clear, continuous long-term upward trend.
• Without adaptation, the economic cost of coastal flooding could reach trillions annually by 2100.

4.4 mm Global Annual Rise

1.94 mm Historic UK Trend

8-9 in Total Rise Since 1880

$14T Projected 2100 Cost

The Viral Hoax: Why Photos Deceive

The core deception of the "then-and-now" photo comparison lies in a fundamental misunderstanding of tides. Sea levels at any specific coastal location change constantly, rising and falling multiple times a day due to the gravitational pull of the moon and the sun. A photograph captures a single fraction of a second in this continuous cycle.

If a historical photo was taken near high tide in 1910, and a modern photo is taken near low tide in 2026, the water level will appear to have fallen. Conversely, matching the exact tide state—down to the minute—is virtually impossible without precise historical records of the exact time the original image was captured. Furthermore, visual analysis cannot account for local weather conditions, atmospheric pressure, or storm surges, all of which temporarily alter water heights.

🔍 Fact Check Focus: The Science of Visual Evidence

Visual comparisons are scientifically invalid for measuring millimeter-scale global trends over a century. To put it in perspective, global sea levels have risen roughly 8 to 9 inches (20 to 23 cm) since 1880. In locations like the UK coastline, the daily tidal range—the difference between high and low tide—can exceed 15 to 20 feet (4.5 to 6 meters).

Attempting to spot an 8-inch long-term rise within a system that fluctuates by 240 inches twice a day using two uncalibrated photographs is equivalent to trying to measure the growth of a blade of grass during a hurricane.

Historic Tide Gauges: The Real Data

Instead of relying on photographs, oceanographers use tide gauges to establish long-term trends. One of the most critical gauges in the world is located at Newlyn in Cornwall, UK. Established in 1915, it provides one of the longest continuous, scientifically rigorous sea-level records in existence. Data from Newlyn was so reliable it was used to define the Ordnance Datum Newlyn (ODN), the official reference point for "height zero" across Great Britain.

The data from the Newlyn tide gauge tells a very different story from the viral memes. When the daily noise of the tides is averaged out over decades, the data reveals a clear, undeniable upward trend: a relative sea-level rise of approximately 1.94 millimeters per year spanning from 1915 to the present day.

Modern measurement systems are even more sophisticated. To ensure absolute accuracy, the Newlyn site has incorporated multiple technologies over the decades:

• Original Stilling Well Gauges: Utilized mechanical floats to measure tidal changes since the early 20th century.
• A Class Bubbler Gauges: Modern pressure systems that provide highly precise pressure-based depth readings.
• Continuous GPS (CGPS): Implemented in 1998 to monitor vertical land movements, allowing researchers to distinguish between actual sea-level rise and local land subsidence.

"When we look at the satellite altimetry data and the historic tide gauge records, there is no ambiguity. The oceans are warming, expanding, and absorbing meltwater from terrestrial ice sheets. The rate of rise has not just continued; it has actively accelerated over the last three decades."

— Leading Climate Scientist, Global Ocean Observing System

Global Satellite Data: The Accelerating Trend

While local tide gauges provide vital historical context, modern understanding of sea-level rise relies heavily on satellite altimetry. Satellites orbiting the Earth use precise radar pulses to measure the height of the entire ocean surface, providing a comprehensive global perspective that cannot be captured from a single harbour.

This global data confirms that the rate of sea-level rise is accelerating. In 1993, the rate was roughly 2.0 mm per year. Today, the long-term expected annual rate has more than doubled to approximately 4.4 mm per year. This acceleration is driven primarily by two main factors:

• Thermal Expansion: As the ocean absorbs excess heat trapped by greenhouse gases, the water physically expands.
• Ice Sheet Melting: The accelerated melting of major land-based ice sheets in Greenland and Antarctica adds new water volume to the global ocean.

Short-term climate phenomena can cause temporary anomalies. For instance, in 2025, a mild La Niña event shifted water from the oceans to land via heavy rainfall in the Amazon, resulting in a temporary lower rise of 0.8 mm for that specific year. Conversely, the preceding year, 2024, saw a massive spike of 5.9 mm due to record ocean temperatures. These year-to-year variations highlight why scientists look at multi-decade averages rather than isolated snapshots in time.

Acceleration of Global Sea-Level Rise Rates (mm/year)

Data compiled from NASA and NOAA long-term altimetry records

The Economic Impacts: The Cost of Denial

Allowing misinformation to dictate public policy carries a massive financial burden. The economic impacts of sea-level rise are projected to grow significantly throughout the 21st century, with costs accelerating sharply after 2050. Projections suggest that by mid-century, urban areas could face global economic costs of around $1 trillion due to coastal infrastructure damage and forced relocation.

By 2100, the figures become catastrophic under unmitigated scenarios. Without aggressive adaptation strategies—such as building robust sea walls, restoring wetlands, and upgrading drainage systems—annual global flood costs could reach between $14 trillion and $31 trillion per year. Some analyses indicate that up to 4% of global GDP could be lost annually to coastal inundation if current trends continue unabated.

The difference between proactive action and denial is stark:

• With Ambitious Adaptation: Strategic investments in coastal defenses can reduce potential economic losses by as much as 95%, safeguarding vulnerable populations.
• Without Adaptation: Nearly 800 million to 1 billion people living in cities and coastal areas by 2050 will be exposed to significantly higher risks of episodic flooding and permanent inundation.

Measurement Methods: Science vs. Social Media

Metric Domain	Visual Photo Comparisons	Scientific Measurement (Satellites/Gauges)	Reliability
Tidal Influence	Highly vulnerable to daily tidal extremes	Averages out noise over decades of data	▲ Leading
Precision	Subjective visual estimation (feet/meters)	Radar altimetry accurate to millimeters	▲ Leading
Global Scope	Limited to a single, hyper-local viewpoint	Comprehensive planetary mapping	▲ Leading
Misinformation Risk	Extremely High (Easily manipulated)	Low (Peer-reviewed, open-source data)	▼ Behind

"Dismissing the reality of sea-level rise based on a Facebook meme is an expensive form of cognitive dissonance. The water is rising regardless of whether we choose to believe the photographs or the data, and the cost of inaction will be measured in trillions."

— Environmental Economist, Global Risk Assessment Council

Ultimately, while two side-by-side pictures of a stone harbour might look compelling on a smartphone screen, they represent terrible science. The reality of a warming planet is captured not in viral memes, but in the painstaking, millimeter-by-millimeter data gathered by satellites in orbit and tide gauges dotting our coastlines. Understanding the difference between anecdotal visuals and empirical data is the first step toward preparing for the profound changes coming to our global shorelines.

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