"Hotspot of accelerated sea-level rise on the Atlantic coast of North America" - final reality check

Last year I shredded the Sallenger et al. paper "Hotspot of accelerated sea-level rise on the Atlantic coast of North America" here. Now, with updated CGPS data from SONEL, I can finally place the headstone on its grave. South of Boston, the coast is subsiding, and subsiding at a generally increasing rate all the way south to Florida. Sandy Hook, a rather inconsequential spot, which all boat traffic in and out of New York harbour pass with barely a glance, had the honour of being one of the few sites along the NW coast with published GPS data. I say had, because SONEL has carried out a massive update of sites worldwide, adding fairly up-to-date data to many. Sandy Hook now has a downloadable record from 1995 to 2013. The record shows that the downward rate has been increasing from less than 2 mm/year in the late 1990s to over 3 mm/year in the three years 2011-2013. I've used the entire record for station SHK5, 2007-2013, which plots at -2.57 mm/year. The SONEL analysis shows -2.65 mm/year, but I've taken account of a few short-term gaps in the data; I assume they didn't. Here's the SONEL plot:

And mine:

Sandy Hook 1993-2015 (Sea-level satellite era):

The relative rate (relative to the tide-gauge/land) is 5.36 mm/year. Absolute rate (relative to the Earth/Geoid) is 2.79 mm/year. The subsidence rate is almost half the relative rate.

The SONEL plot for New York Battery Park, where both tide-gauge and GPS pillar are located:

The rate during the late 1990s was around -1 mm/year. My analysis:

The chart for New York (Battery Park) 1993-2015:

Relative rate is 3.92 mm/year; absolute rate, allowing for subsidence of 1.93 mm/year is 1.99. The "Hotspot" isn't one of sea-level rise, but one of subsidence. Sallenger et al. were also being somewhat disingenuous when they claimed that the rates of subsidence along the coast "were almost constant", and therefore didn't affect their complex analysis or results. They weren't constant when the paper was written, and the rates are generally increasing over the last 20 years; some very little, some like New York and Sandy Hook, significantly increasing. The "Hotspot" was an artefact of questionable and almost impenetrable analysis, ignoring the inconvenient past, and coastal subsidence.

Note also the obvious cycles which appeared in the record after 1970 - large and small alternating. Sallenger et al. used PSMSL annual average data, and so they wouldn't have been obvious. Take some data and torture it using complex and (to me, impenetrable) statistical techniques I imagine most sea-level experts and authors couldn't fathom, and get the answer you want. What I do know is that those techniques aren't suited to relatively small datasets, which is what you have if you use annual average data. Also PSMSL omit years from annual data, even if just one month is missing. The annual data Sallenger et al. used had quite a few years missing, shrinking their database even further.

Something else Sallenger et al. failed to mention is that a comparable rate of rise occurred before the mid-1950s. Somehow their "long-term" analysis wasn't quite that long:

Trend, in mm/year for 30-year sliding window, end year on x-axis.

The red circle marks 2009, the end year for the "Hot-spot" analysis. It's easy to see the rate of increase was much higher prior to 1953. If the whole record shows an inconvenient truth, just analyse part of it.

NASA scientist makes a booboo

Back in 2012, when so-called "Superstorm" Sandy was current news, there were lots of dire predictions of "What is to come". At the time, I bookmarked several newspaper, blog, and other articles. While I was sorting out my links, discarding purely alarmist, inaccurate, and dead pages, I came across this one, and spotted something significant I'd missed at the time. Titled "Superstorm Sandy and Sea Level Rise", an interview with Cynthia Rosenzweig, "a climate impacts expert at NASA Goddard Institute for Space Studies, co-chair of the New York City Panel on Climate Change, and director of the NOAA-sponsored Consortium for Climate Risk in the Urban Northeast.". Wow - she must really know her stuff? She certainly appears to, here's her response to the question 

What kind of sea level rise has New York Harbor seen over the past century?We’ve had roughly a foot of sea level rise in the New York City area in the past century. That’s measured at a tidal gauge near Battery Park just off the southern tip of Manhattan.
The majority of the sea level rise in the New York City region is due to global warming: primarily, because of thermal expansion of ocean water as it warms and secondly, melting of land-based ice sheets.
Land subsidence [sinking] in the New York City area has been roughly 3-4 inches per century, which is primarily due to the Earth’s crust rebounding* from being compressed by massive ice sheets that covered Canada and the northern U.S. about 20,000 years ago near the end of the last Ice Age. Local variations in ocean surface elevation associated with the strength of the Gulf Stream has played a small role as well.

That's fine, but later

How does sea level rise in New York Harbor compare to other parts of the U.S.? What about the global average? Sea level isn’t rising evenly throughout the world. On average, global sea level has risen about eight inches since 1880. So, the New York rate of sea level rise of nearly one foot is higher than the global average rate.

Just a cotton-picking moment, she said that land subsidence in the New York City area was 3 to 4 inches over the last century. That makes true sea-level rise at New York 8 to 9 inches, compared with the global rate of 8 inches since 1880. There was very little if any rise anywhere in the world between 1880 and 1912, a hundred years back from when this article was written. 12 inches is certainly much higher than the 8 for global, but the true comparison is between 8-9 inches and 8 inches. I hope this was a simple mistake. For now, I'll give her the benefit of the doubt.

"Hotspot of accelerated sea-level rise on the Atlantic coast of North America" - finally laid to rest. RIP

There's been some discussion about sea-level rise on the Eastern seaboard of the U.S. in the comments on the recent "Doubling up the sea level scare for Paris using the old ‘one-two punch’ line" post at WUWT. I posted a couple of charts there, and I intend to return to the Sallenger et al article in this post's title. They used windows of  60, 50 and 40 years for their analysis, and showed this chart for New York; incidentally the only time-series chart in the entire article - rather surprising since they analysed dozens of gauge stations around North America.

Supplementary Figure S7.  New York City annual average sea level data with three
regression results used in this study for the most recent 60-year subsample (1950-2009).
The mean elevation of the annual NYC sea level data (1893-2009) was removed and time
t = 0 was set at year 1950 (t = year – 1950) for these regressions.

I'm in the habit of using a variety of techniques to analyse gauge records, especially long ones like New York, as I did in a previous post about the "Hotspot". Those two 30-year regression lines above prompted me to plot a 30-year sliding window for New York, using the data from 1893-2013, slightly longer than Sallenger et al, who used PSMSL annual average data to 2009 - I've used annual averages calculated from monthly data. Their data had three recent years missing because a few monthly data points are missing, and PSMSL exclude such years. I suspect the differences are small though.

Data from PSMSL

The first thing that's obvious is that 30-year periods ending in the 1950s actually had rates higher than the 1980-2009 period shown on their chart above. So the modern acceleration is nothing new; in fact the earlier acceleration was more rapid. It also shows that projecting a 30-year rate forward to 2100 is both unscientific and ignoring history completely. I certainly don't expect future years to mirror the big fall in rates after the mid 1950s, but I do expect something of a drop. Sallenger et al just didn't look for any cyclical pattern in the gauge data. They mentioned it was possible that there were such patterns, but their analysis was effectively designed to mask it by comparing differences in rate between adjacent windows. If that was plotted, the 1950s peak above would be a trough! Why do I expect a gradual drop in rate? Because it's already underway!

Rates (mm/year) for 10 year (121 month) sliding windows.

Note how irregular peaks "kicked in" at the end of the 1960s; the latest peaked after Sallenger et al's 2009 end date, in 2010/11. Sandy Hook is an island S of the entrance to NY harbour. A more up-to-date (to 2014) plot shows the descent from the last peak more clearly:

Rates (mm/year) for 10 year (121 month) sliding windows.

Finally, here's the rate evolution, Rates are computed from 1950; the final point is 2014. When I've time, I'll update all my NY charts to date, and replace any above that need it.

In 2009, the rate was still rising; now it's levelled off. Sallenger et al's projection is already out-of-date. RIP