# Sea Level: Eastern North America

Since Dave Burton was kind enough to remind us how great the danger of sea level rise is, I’m enjoying the recent focus on the topic. I’d like to apply my new alignment technique (including variable station weights) to several regions of eastern North America, to see how they differ and what they have in common in their sea level history.

I’ll even form a composite mean for all eastern North America based on the five regional means, which is a little bit like area weighting — the regions aren’t really right for that, but at least we’ll be able to compensate to some degree for the concentration of stations in a few regions.

Here are the resulting time series for each region, and I’ve offset them so they don’t plot on top of each other:

In region 2, sea level is rising faster than the others. I note that both regions 3 and 4 show a spike in sea level in 1948 which is not present in the other regions.

A glance at the map above shows that region 2 also has a large number of stations. This means that when forming a composite average, the fast-rising region can be over-represented. This can be confirmed by comparing the composite based on all the stations, to the composite based on combining the five separate regions with equal weighting. And here they are:

The red curve is labeled “Area Weighted” but it really means based on the five regions rather than all the stations together, which is called “Not”.

We can also look at how each region deviates from the composite average, which underscores the rapid sea level rise in region 2, compared to the rest:

It’s interesting to compare the rates for the different regions:

All of them except region5 (which is really islands) show a pronounce episode of rapid rise around 1940. And of course we can compute the rate for the composite:

Based on recent requests for data, I suspect some of you want to play around with things yourself. I might have solved the problem of sharing text files without WordPress getting in the way. If I’ve got this right, you can get:

Reconstructions for the N.Amer regions here

Stations used in North America: here

Code for vw.align.r program (hopefully, with indentation intact): here

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### 7 responses to “Sea Level: Eastern North America”

1. DaveX

Are the deviations(mm) by region offset by 100*n?
As a NAmer2 resident I know that we have high relative sea level rise, but I like the way you present the evolution over time. I’ve been using the 5.2mm/year rate from the Sewell’s point gauge at https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?id=8638610 from the “Variation of 50 year RSL trends” tab as support to tell people that the rise is about half a foot over the course of a 30 year mortgage, which is significant for the lowlying waterfront around here.

The near 6mm/year point estimate for NAmer2 would be closer to 7″ than 6″ over the course of a 30 year mortgage That’s high enough to make planning retirement around paying off an oceanfront house into a stupid investment.

2. David B. Benson

NAmer2 the most? I opine that is the result of hot air from Washington, DC. :)

• DaveX

As a NAmer2 resident, “Glacial Isostatic Adjustment” is the common explanation.

• J W Owens

Combination of GIA and Chesapeake bolide crater in the region, Dave
The post replicates a fair amount of work on the East Coast from GPS measured rise to paleoclimate sea level rise (see Kemp, Englehart, Peltier and others – example Karegar et al Geophys Res Lett 43:3126-3133 2016)
King tide flooding in Virginia Beach and surrounding area problem just like Miami area

3. Keith R-D

Have you looked at the estimates of the rates of vertical land movement that come out of this procedure (your $-\beta_A$ from your post describing your alignment method)? Do they agree with what you might expect from glacial isostatic rebound, sediment deposition and loading, etc.?

[Response: Not in detail — but I have mapped where the rates, and it’s abundantly clear that they agree with “overall” GIA values, i.e. the land is rising fastest where the ice sheets used to be, and sinking fastest where we expect (south of the terminus of the Laurentide ice sheet, etc.). It would definitely be worthwhile to make a detailed comparison.]

• J W Owens

Per reply above – see Karegar et al “Subsidence along the Atlantic Coast of North America: Insights from GPS and late Holocene relative sea level data” Geophys Res Lett 43:3126-3133 2016 + references and citations, of course

4. Thanks for writing on this topic. I live in New York City, and it feels like Coastal Flood Advisories and Warnings have become a lot more common in recent years, just even for regular high tides. It’s quite alarming, and it’s getting worse, not better.