Earth's Mantle Affects Sea Levels

For archival purposes, Yahoo!News is reporting:

A prehistoric shoreline runs along the eastern edge of North America; scientists have pointed to it as evidence that much of Antarctica melted 3 million years ago. But new research suggests this shoreline is actually about 30 feet (10 meters) lower than previously thought, meaning less ice melted than suspected.

The shoreline, which should be flat, also swoops up and down the East Coast like a set of wave crests, reflecting tugging and pushing by Earth's mantle, the layer of viscous rock leisurely oozing underneath the crust, according to the study, published today (May 16) in the journal Science Express.

The finding shows that scientists have to be careful when looking at Earth for evidence of past sea level changes from the planet's cycles of glacial advance and retreat.

And then this very disturbing fact:

"You simply can't go somewhere and look at the height of the shoreline and infer anything about the amount of water in the oceans or the height of sea level without already knowing an awful lot about what the mantle is doing," said David Rowley, lead study author and a geologist at the University of Chicago.

Why is that so disturbing?

Back on November 29, 2012, just have Thanksgiving, I wrote:

The oceans have risen an average of 3 millimeters / year since 1992. That's from the linked article. Three millimeters.

 Twenty percent of 3 mm --> 0.6 mm.

Some years ago, I put a popsicle stick in the sand at Cabrillo Beach, San Pedro, California, to measure the rising ocean. I marked the stick in one (1) millimeter hash marks. Unfortunately, I used water-soluble ink. My experiment gone awry. But I digress.

0.6 mm/year. Reproducible? Hardly. Statistically significant? Unlikely.

0.6 mm / year. But this is the scary part, from the linked article:

“Most people think they don’t have to worry about it, because it’s just a few millimeters,” he said. “But every inch we get makes a storm surge worse.”

Look at Hurricane Sandy. 

So, I will have to tell our granddaughters the unfortunate news that placing a popsicle stick in the sand at the beach is not accurate for measure the rise of global sea levels.

That's too bad. It seemed so simple.

I wonder if that popsicle stick is still there?

By the way, can we read that interesting line from the first paragraph again? Sure:

" .... this shoreline is actually about 30 feet (10 meters) lower than previously thought, meaning less ice melted than suspected."