Maine marine geologist: No mistaking rising sea level

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SOUTH PORTLAND — A century’s worth of local sea level data fell into Peter Slovinsky’s lap earlier this year, so he did what any scientist worth his salt would do.

He crunched it.

The results are incontrovertible, he said: Sea level is rising.

“It’s a scientific fact,” Slovinsky said. “It is rising and we’re probably going to see an increase in storm events.”

Slovinsky shared his findings in a packed classroom during the Maine Beaches Conference at Southern Maine Community College on July 12. The conference featured a full day of seminars on everything from the lessons from Superstorm Sandy, to rising insurance costs for coastal property owners, to coastal Maine tourism.

Slovinsky, a marine geologist with the Maine Geological Survey, took his data from a single stalwart source: a 101-year-old tide station at the Maine State Pier in Portland.

The gauge, which is owned by the National Oceanic and Atmospheric Administration, has been measuring water levels every hour since 1912. In recent decades, the station began recording water levels every six minutes. Overall, the station provided Slovinsky with 390,000 lines of data, which he analyzed.

“I had time, so I did it,” he said.

The tide station shows that the sea has risen more than half a foot in the past 100 years and the pace has accelerated, he said. Every year since 1912 the water level has risen an average of 1.1 millimeters.

“It doesn’t sound like much, but when you extrapolate that over a century, it’s about 7.5 inches,” he said.

In the past 20 years, sea-level rise has sped up to a yearly average of about 3.5 millimeters, which is faster than any period during the past 5,000 years, Slovinsky said. During the same 20-year period, the rate of sea level rise in Maine has been faster than the global average: 4.5 millimeters per year.

If it continues at its current speed, sea level will rise in Maine at a rate of 17 inches per century.

The rising water could prove disastrous.

In Portland, for instance, flood stage is 12 feet. According to 2011 statistics, flood stage was exceeded in Portland 11 times, or 1.6 percent of all tides. If the average sea level had been a foot higher in 2011, flood stage would have been exceeded 100 times, or 14 percent of all tides. If sea level had been two feet higher, flood stage would have been exceeded 300 times, or 40 percent of all tides, Slovinsky said.

“That’s pretty significant if you’re trying to have businesses along the waterfront,” he said.

Slovinsky said when the sea level rises 1 foot higher than the current level, the Maine coast will experience every 10 years what is now considered a 100-year coastal flooding event. For instance, the Blizzard of 1978 was a 100-year event that had an overall water level of 14 feet. The Patriot’s Day Storm in 2007 was a 10-year event with an overall water level of 13 feet – a one-foot difference.

The good news for Maine is our relatively large tidal range, he said. In Portland, for instance, the average range is about 9 feet. It is rare that the largest storm surges in the last 100 years coincided with high tides.

Superstorm Sandy caused massive storm surges in New York and New Jersey, but in Maine it was hardly felt. The storm surge on our coast was 3.2 feet, and it occurred at low tide.

“We had a lot of beach erosion, we had a lot of wave impacts, but nothing from storm surge,” he said.

Sea level in Maine also varies by month and season. Water level is highest in May, June and July because wind causes water to pile up at the coast.

“One of the reasons we’re famous for our sailing is because we have consistent onshore winds that blow in the summer months,” Slovinsky said.

Ben McCanna can be reached at 781-3661 ext. 125 or [email protected]. Follow him on Twitter: @BenMcCanna.