A viral Facebook post claims sea levels were lower in 2019 than they were 100 years ago.
The claim has been added at the start of a viral letter, previously debunked by AAP FactCheck, which attacks the viability of renewable energy and the severity of climate change. The post has recently circulated again on Facebook.
“100 YEARS OF STUDY OF THE MEAN SEA LEVEL ACTUALLY LOWER IN 2019 BY 6 CM THAN 100 YEARS AGO,” a section of the post reads.
But the claim is false. Data published by Australia’s national science agency, the CSIRO, shows sea levels have risen by more than 20 centimetres in the 100 years to 2019 while the United Nations’ Intergovernmental Panel on Climate Change (IPCC) made a similar finding in 2021.
According to the CSIRO’s State of the Climate 2020 report, ocean levels have consistently risen over the last 140 years: “Global mean sea level has risen by around 25 cm since 1880; half of this rise has occurred since 1970.”
The report added: “Global mean sea level rise is accelerating. Tide gauge and satellite altimetry observations show that the rate of global mean sea level rise increased from 1.5 ± 0.2 cm per decade (1901-2000) to 3.5 ± 0.4 cm per decade (1993-2019). The dominant cause of global mean sea level rise since 1970 is anthropogenic climate change.”
Climate and ocean experts confirmed the conclusions of the CSIRO report and told AAP FactCheck that sea levels have risen consistently during the last 100 years.
Dr Alex Sen Gupta of UNSW’s Climate Change Research Centre, whose research focuses on the role of oceans in the climate system, told AAP FactCheck: “We have clear evidence that sea level has risen by over 20cm globally since the industrial revolution.”
Dr Sen Gupta added in an email: “We can see this in tide gauge records from around the world (some of which have records extending back over 100 years). We can also see this using satellite data that provides very accurate global sea level measurements since the 1990s.”
The UN’s IPCC released a report last year stating that sea levels rose around 20cm in the last 100 years.
“Global mean sea level (GMSL) rose faster in the 20th century than in any prior century over the last three millennia (high confidence), with a 0.20 (0.15 to 0.25) m rise over the period 1901-2018 (high confidence),” the report said (page 1216).
“GMSL rise has accelerated since the late 1960s, with an average rate of 2.3 (1.6 to 3.1) mm yr-1 over the period 1971-2018 increasing to 3.7 (3.2 to 4.2) mm yr-1 over the period 2006-2018 (high confidence).”
It adds: “Human influence was very likely the main driver of these increases since at least 1971” (page 5).
Dr Richard Jones, a research fellow at Monash University’s School of Earth Atmosphere and Environment, summarised the findings by telling AAP FactCheck that “even by the smallest estimate, global mean sea level has risen by 0.15m since the start of the 20th century, but possibly as much as 0.25m.”
Dr Jones added that greenhouse gas emissions have played a clear role in the increase, illustrated by a graph in chapter three of the UN report (figure 3.29, page 482).
“It shows simulated (coloured lines) and observed (black line; 1971-2018) sea-level change. The black line overlaps the orange line, demonstrating that sea-level change since at least the 1970s can only be explained by a combination of natural and anthropogenic factors (i.e. greenhouse gas emissions were a key driver of past sea-level rise),” he said in an email.
Dr Felicity McCormack, an Antarctic research fellow at Monash University, agreed and said via email: “The IPCC Special Report on Oceans and Cryosphere in a Changing Climate also makes a clear link between sea level rise and anthropogenic climate change, with high confidence that global mean sea level rise is attributable to anthropogenic greenhouse gas emissions.
“This means that we will continue to see sea level rise as a result of anthropogenic climate change.”
AAP FactCheck previously debunked a similar claim on sea levels in Sydney Harbour.
The claim that sea levels were lower in 2019 than they were 100 years ago is false. Data from the CSIRO and the UN’s Intergovernmental Panel on Climate Change shows that mean sea levels rose around 20cm during the same period and have consistently risen over the last 100 years.
False – The claim is inaccurate.