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Sea-level data shared by climate skeptics omits global trend

Sea-level data shared by climate skeptics omits global trend - Featured image

Author(s): Roland LLOYD PARRY / AFP USA

Videos shared by a Canadian climate-skeptic website present charts showing oceans are rising negligibly or even retreating in some parts of the world. But the clips lack context about the overall trend and selectively highlight a few locations; global data indicates average sea levels are rising and pose dangers to many coastal communities.

“In this weekly feature from the Climate Discussion Nexus, we check claims of relentless sea level rise against actual data,” says the caption of a YouTube video published March 14, 2023.

The clip, titled “Sea Level Check – Scandinavia,” shows Google Earth imagery of Norway, Sweden and Denmark interspersed with screenshots of data from the US National Oceanic and Atmospheric Administration (NOAA).

A narrator says that, in the capital of Sweden, “the record shows that sea levels are falling at an annual rate of 3.77 millimeters a year.”

“That’s right: a century from now, Stockholm can expect sea levels to drop by 1.24 feet, or 37.79 centimeters for you metric folks,” the narrator says. “Owners of ocean-front property are strongly advised to stay where they are, listen to some music and pour yourselves a nice glass of brannvin (liquor).”

Screenshot of a Climate Discussion Nexus video taken April 14, 2023

CDN published the video and others like it online, including on Facebook. Other clips in the series cite sea-level trends for cities such as Sydney and Vancouver, as well as Microsoft co-founder Bill Gates’s seaside home in the US state of California.

CDN says on its website that it was “formed in 2018 by a group of citizens concerned about expensive, ill-planned energy policies intended to reduce carbon dioxide emissions.” The group has previously spread misinformation about global warming.

Commentators contesting climate-related measures or seeking to downplay the dangers of global warming have repeatedly said sea-level rise is negligible. AFP has fact-checked similar claims as misleading.

NOAA pointed AFP to data (archived here) that show global sea levels are rising, increasing the reach of storm surges that cause flooding inland.

“Sea level rise at specific locations may be more or less than the global average due to local factors such as land subsidence from natural processes and withdrawal of groundwater and fossil fuels, changes in regional ocean currents, and whether the land is still rebounding from the compressive weight of Ice Age glaciers,” the agency says on its website.

Land rebounding

The CDN video about Scandinavia selectively highlights places where the lingering effects of ancient glaciers affect sea-level trends, experts told AFP.

“The Scandinavian locations in the video are all areas where the land is rebounding — rising up out of the ocean — faster than the ocean is rising,” said William Sweet, an oceanographer for NOAA’s National Ocean Service, in an email on April 11, 2023. “In these areas, relative sea level rise is either flat or even dropping because of this phenomenon.”

Sweet said the land is rebounding because “it is adjusting after the compressive weight of glacial ice that was present thousands of years ago during the last Ice Age has melted.”

Change in sea levels from 1993 to 2022 – AFP

“This is also happening in some areas in Alaska and Canada,” he said. “Additionally, there are other regions of the world where tectonic shifts can also cause land to rise up and create apparent drops in relative sea level.”

Other locations are threatened by a sharp rise in sea level, however.

For example, the level is rising by more than 14 mm per year in Manila and more than 7 mm per year in Fiji, according to the same NOAA database cited in the CDN videos.

Sea-level rise accelerating

Oceans rise and fall over time as ice sheets melt or grow due to solar cycles. Research indicates global sea levels have risen by 120 meters (400 feet) since the last ice age.

The increase in average ocean levels is driven by the melting of glaciers and ice sheets due to human-caused emissions, according to a 2019 report from the UN Intergovernmental Panel on Climate Change (IPCC).

The IPCC’s 2021 report said the average rate of sea level rise increased from 1.3 mm per year from 1901-1971 to 1.9 mm per year from 1971-2006. It reached 3.7 mm per year between 2006 and 2018.

“Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3,000 years,” the report said.

The sea level has risen on the French Caribbean island of Martinique – STEPHANE DE SAKUTIN / AFP

The IPCC’s reports are produced by hundreds of scientists who review thousands of studies.

The panel projects that, by 2100, the global mean sea level will rise 38-77 centimeters from the 1995-2014 average, depending on the status of human-caused carbon emissions. But not all regions will be affected the same.

“Sea-level rise is not globally uniform and varies regionally,” the report said, in part due to “thermal expansion, ocean dynamics and land ice loss.”

Dangerous, costly

The 2019 IPCC special report projected extreme high tides and storm surges will hit “many low-lying cities and small islands” annually by 2050. Without adaption measures, this could “increase expected annual flood damages by two to three orders of magnitude by 2100.”

“Effective protection requires investments on the order of tens to several hundreds of billions” of dollars per year globally, the report said.

A 2014 study estimated the cost of future sea-level rise and associated disasters in the United States, including adaptive measures, at around $1 trillion.

Sea-level rise worsens storm surges like the one that struck when Hurricane Michael hit Florida in October 2018 – ANDREW CABALLERO-REYNOLDS / AFP

Under the 2015 Paris Agreement, countries have pledged to reduce greenhouse gas emissions to limit the rise in global temperature to 1.5 degrees Celsius and curb the impact of climate change.

AFP has fact-checked other climate-related claims here.

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Originally published here.