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Photos of water at Sydney Harbor fort do not refute sea level rise

July 22, 2022 GMT

CLAIM: Photos taken a century apart at Fort Denison in Australia’s Sydney Harbor are proof that climate change has not led to higher sea levels there or at other monuments near water.

AP’S ASSESSMENT: False. Sea levels at that site have risen and continue to rise, measurements show. Additionally, historical photographs used to support the claim are not a reliable indicator of rising sea levels, scientists say. Tides, seasonal weather patterns and other factors make a direct comparison between photos impossible.

THE FACTS: As a record-breaking heat wave scorches Europe and the dangers of human-driven climate change continue to mount, posts expressing skepticism about whether sea levels are rising at various coastal landmarks are being resurrected on social media.

One prominent example compares two photos of Fort Denison, a former Australian military site built on a small island in the mid-1800s. The water level at the shore beneath the fort appears to be roughly the same in both photos, though the post claims they were taken more than a century apart. Sea levels at Sydney Harbor have risen “approximately 0.0 cm over the past 140 years,” the photo caption reads.

But sea levels at Fort Denison are rising, government statistics show. The mean, or average, sea level trend at the site shows a slow rise of approximately 0.8 millimeters (.03 inches) per year since 1886, according to data aggregated from the U.S. National Oceanic and Atmospheric Administration and the United Kingdom-based Permanent Service for Mean Sea Level. Measurements from the Australian Bureau of Meteorology dating back to 1912 also show a subtle increase in mean sea level.

Global sea level has risen on average by more than 8 inches since 1880, with about one-third of that occurring in the last 25 years, according to NOAA.

John Church, professor emeritus at the University of New South Wales, told The Associated Press in an email that the rate of increase in Australia is still slower than the global rate, but has accelerated in recent decades.

The Fort Denison post has spread since at least 2019. Similar posts comparing old and new photos of Sydney’s Palm Beach and Plymouth Rock in Massachusetts have also resurfaced recently on social media.

Karin Bumbaco, assistant state climatologist of Washington, said that photos of landmarks can be “cherry-picked” to downplay the effects of climate change.

“There are daily tides that impact sea level as well as seasonal changes so that in order to really compare photos, there’s a need to know what time of year and even the time of day that an old photo was taken to compare them,” she said.

Numerous other factors determine changes in sea level.

These include “storm surge, heating and cooling of the ocean with the seasons, El Nino cycles, vertical land movement, and many other effects,” Tom Connolly, an oceanographer and an assistant professor at San Jose State University, told the AP in an email.

“Comprehensive studies on regional sea level rise use long-term data from tide gauges (thousands or even millions of data points per site),” he added, “and more recent data from satellites, as well as geological and atmospheric data.”

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This is part of AP’s effort to address widely shared misinformation, including work with outside companies and organizations to add factual context to misleading content that is circulating online. Learn more about fact-checking at AP.