Climate science is sound. Satellite timelapse doesn't disprove sea level rise | Fact check

Kate S. Petersen, USA TODAY
·5 min read
20

The claim: Satellite image timelapse of coastline shows climate change isn't happening

An April 9 Instagram video (direct link, archive link) shows a timelapse of satellite images of urban development near the coast in Tulum, Mexico, from 1984 to 2022. While the position of the coastline appears to waver a bit, it does not obviously move inland.

"Shocking NASA footage showing how the sea level has risen in the last 40 years," reads the caption. "All a bloody con this #climate lark."

Another version of the claim shared on Instagram garnered more than 220,000 likes in a month.

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Our rating: False

Average sea levels have risen worldwide due to global warming, according to research. A satellite image timelapse of one city's coastline is not enough to determine whether or not sea level rise has occurred, experts said. Multiple lines of evidence, including sea level rise, show that Earth's climate is changing.

Sea level change cannot be diagnosed through satellite images of one beach

Global warming results in sea level rise because water expands as it warms and melting ice sheets and glaciers increase the amount of water in ocean basins. Tide gauge and satellite data show that average global sea levels have risen 8 to 9 inches since 1880, according to the National Oceanic and Atmospheric Administration.

There are several reasons why satellite images of one coastline are not an adequate way to detect this rise, researchers told USA TODAY. First, sea level rise may not obviously change the profile of a given beach if the area is being adequately replenished with sediment, Robert Kopp, a climate change scientist at Rutgers University, told USA TODAY.

"It’s close to a fool’s errand to try to identify sea-level change from landscape-level imagery because sea-level change is just one input into landscape change," he said. "Beaches erode and are replenished from sediment supply all the time. Sea-level rise increases erosion, but if the sediment supply keeps pace, you can still get a steady state profile. It’s the balance between the two that matters."

Second, depending on different factors, satellite images may not have the resolution to show encroachment, Don Chambers, a physical oceanographer at the University of South Florida, told USA TODAY.

"Imagery is not used to measure sea level rise," he said. Instead, "we bounce microwave radar signals off the ocean surface from a satellite and deduce the range from the water level to the satellite. We can know the precise location of the satellite above the center of the earth − to within 1 centimeter vertically using GPS tracking − and thus determine the height of the water above the center of the earth."

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Vertical land motion − land rising or sinking due to geological factors or human behavior − is yet another reason that images from one beach are inadequate to assess the existence of sea level rise. If land is rising in an area, local sea levels can be falling relative to the land, even while the global average is increasing.

"Sea level rise is also not uniform everywhere because of wind and ocean current patterns," Chambers said. "Sea level along the east coast of the United States is rising a little faster than along the west coast for this reason."

Tulum doesn't have a tide gauge station, Chambers said. But the closest stations in Progresso, Mexico, and Cape San Antonio, Cuba, have both measured steady sea level rise.

Global sea level rise is only one symptom of climate change

Rather than drawing conclusions from images of one stretch of coastline, scientists have determined that Earth's climate is changing by analyzing multiple lines of evidence. For instance, in addition to documenting global sea level rise, multiple climate agencies have detected a long-term rise in global temperatures.

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Researchers have also documented:

The Instagram user who posted the video did not immediately respond to a request for comment.

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This article originally appeared on USA TODAY: No, satellite timelapse doesn't disprove climate change | Fact check