Do two photos of Palm Beach, in New South Wales, Australia, purportedly taken almost a century apart, prove there has been no change in the sea level and that climate change is a hoax? No, that's not true: An overall change in sea level over the course of a century can not be measured by comparing two photos and Australia's Bureau of Meteorology has documented the rise of the sea that surrounds that continent.
The changing width of a sandy beach does not convey information about the change in sea level over the course of a century nor does it show that a major effort was made decades ago to restore and preserve this isthmus that links Palm Beach to Barrenjoey Head.
The claim appeared in a Facebook post (archived here) on April 19, 2021. The text in the meme reads:
99 Years of sea level rise
Palm Beach Sydney
1917 - 2016
For years they called it Global Warming. But they were proven over and over that no such thing is happening. Then they started calling it Climate Change. Again it is a hoax.
This is what the post looked like on Facebook on April 23, 2021:
(Source: Facebook screenshot taken on Fri Apr 23 19:18:32 2021 UTC)
To be useful, a pair of comparison photos would at least have to be taken at the same tide level near the same day of the year.
Palm Beach has two high and two low tides a day, with a varying change in water level of typically about 5 feet 9 inches every six hours, which could change the apparent width of the isthmus.Not only are tides always changing the waterline at the shore- the beach itself is variable and can be changed by storms, ocean currents, longshore drift, and actions by people, which can change the lateral movement of beach-building sand and sediments.
Since 1917, the global sea level has risen more than 8 inches, according to charts maintained by the National Oceanographic and Atmospheric Administration, with the rate of increase accelerating in recent decades.
The Australian Bureau of Meteorology has also measured the rise of sea level. The agency issued a report on the "State of the Climate 2020" which includes charts specific to Australia. One chart shows the rate of the sea level rise along different parts of the Australian coast which was measured with satellite altimetry from 1993 to 2019. The coastline near Sydney shows some of the highest rate of increase in Australia, about 3 inches per decade. In the section on oceans two issues covered are ocean temperature and sea level, which are linked because water increases in volume as it warms:
As the ocean warms it expands and sea level rises. This thermal expansion has contributed about one third of the sea level rise observed globally, around 25 cm since the late 19th century. Ice loss from glaciers and polar ice sheets, together with changes in the amount of water stored on the land, contribute the remaining two thirds of the observed global sea level rise. Ice loss from Greenland, Antarctica and glaciers has been the dominant contributor to global sea level rise from 1993 to the present.
The "State of the Climate" report documents how the rate of the rise in sea level is accelerating and notes that tide gauges and satellite altimetry have improved the accuracy of sea level measurement. For instance, the Sentinel-6 Michael Freilich satellite was launched from Vandenberg Air Force Base in California On November 21, 2020, as part of a joint mission between NASA, the European Space Agency and several other agencies to observe the Earth's oceans and atmosphere.
These two photos in the meme looking south toward Palm Beach were taken from nearly the same vantage point near the top of a steep rocky "head" named Barrenjoey where there is a historic lighthouse, now part of the Ku-ring-gai Chase National Park. Lead Stories was unable to verify the dates of either photo, but a December 19, 2014, Dailytelegraph.com.au article on "The thin strip of sand the binds Barrenjoey Head to the mainland" contains many photos of the sandy strip from the early 1900s.
The article explains that Palm Beach and Barrenjoey were not always connected:
Over thousands of years, the sand spit slowly stretched north until it reached Barrenjoey, which became a "tied island" linked to Palm Beach by the isthmus of sand. Once the isthmus had formed, it was consolidated by sand building up on both the ocean and Pittwater sides, and by the clothing of vegetation that crept slowly northward from Palm Beach to stabilise the sand.
The article explains some of the ways human activities resulted in the height of the sand strip decreasing from 33 to 39 feet tall in 1876 to just 16 to 29 feet tall in 1977, and then the efforts to restore and preserve the sand, which were implemented in the late 1970s and early 1980s. In comparing the photos in the meme, the before and after change of the restorative vegetation is clearly visible in the color photo.