Mean Sea Level at Alert, Canada (NOAA 970-162, PSMSL 1110)

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The mean sea level (MSL) trend at Alert, Canada is -2.34 mm/year with a 95% confidence interval of ± 1.07 mm/year, based on monthly mean sea level data from 1969 to 2018.‡ That is equivalent to a change of -0.77 feet in 100 years. (R‑squared = (?))

The plot shows the monthly mean sea level without the regular seasonal fluctuations due to coastal ocean temperatures, salinities, winds, atmospheric pressures, and ocean currents. By default, the long-term linear trend is also shown, in red, along with its 95% confidence interval. The plotted values are relative to the most recent Mean Sea Level datum established by NOAA CO-OPS.

Options

Show calculated linear trend (linear regression)
Show linear trend 95% confidence intervals†
Show linear trend 95% prediction intervals†
Show quadratic regression
Show quadratic trend 95% confidence intervals†
Show quadratic trend 95% prediction intervals†
Show NOAA's linear trend
Show NOAA's linear trend 95% confidence intervals
Show CO2 levels
Boxcar smoothing: Enable Width: Repeat:
Line weight: thin medium thick color scheme:

Graph from:	start date	thru end date
Calculate using:	start date	thru end date
Show MSL from:	start date	thru end date

Data source: NOAA PSMSL NOAA,PSMSL PSMSL,NOAA

Draw projection: none linear const accel
From:	start date	MSL (meters)	Slope (mm/yr)
To:	end date	MSL (meters)

Height: pixels (default 450).
Width: pixels (default is determined by window width).
Or, to change graph width, resize browser window and click:

Data source: ? months from NOAA + ? months from PSMSL.

Click here for a downloadable, bookmarkable image (except in Internet Explorer or Microsoft Edge, use PrtScn, or see NOAA's version, or PSMSL's version.)

For a simple explanation of the meaning of the 95% confidence & prediction interval traces shown in the graph, see this two-minute instructional video, by Dr. Gerard Verschuuren.

Regressions
Linear:
y = B + M·x
y = B + M·x mm
Quadratic:
y = B' + M·x + A·x²
y = B + M·x + A·x² mm
where:
Date range = (1935) to (2015)
x = (date - avg(date)) (date)
slope = M = ± mm/yr
acceleration = 2·A = 2×A = ± mm/yr²

To see precise values, hover your mouse cursor over the graph traces (or touch the graph on a touch-screen).

To download the seasonally-adjusted monthly MSL data from NOAA in CSV format click here, or for unadjusted ("raw") data click here.

We also have a graph of just carbon dioxide (CO₂) levels, and a combined graph of CO₂ and CH₄.

†Calculation of Confidence Intervals and Prediction Intervals for monthly Mean Sea-Level (MSL) is complicated by the fact that MSL measurement data is serially autocorrelated. That means each month's MSL measurement is correlated, to an extent which varies by location, with the MSL measurements of the previous and next months. That means there are effectively fewer independent measurements, which would cause a naive confidence interval calculation to underestimate the breadth of the intervals. The code here follows the method of Zervas 2009, “Sea Level Variations of the United States 1854-2006,” NOAA Technical Report NOS CO-OPS 053, p. 15-24, to account for autocorrelation, when calculating confidence intervals and prediction intervals. That isn't the only way to do it, though, and one of the items on my to-do list is to examine an alternative approach suggested by Willis Eschenbach.