Across the globe there exist only a handful of tide gauge station records available that exceed 100 years in length, and that also report at least 90% of the monthly records over the last 100 years.
Using the Permanent Service for Mean Sea Level (PSMSL) database, one can identify 15 gauge sites that are exemplary in record keeping. In addition, all 15 have records through 2013, with the majority (12) having records through 2014.
The 15 sites with a long history of gauge readings are listed on the adjacent chart. The chart also includes an average of all 15 and a plot of atmospheric CO2 levels.
The chart plots the per century trends, by month, based on moving 30-year (360-month) periods.
The smooth trend curves plotted are fitted, providing a visual as to where sea level acceleration and deceleration have been, and indicate where they might be going. [Ed: Using trends for predictive purposes is not recommended.]
The purplish (mauve) smooth curve is the average of all moving per century trends for the 15 sites; the monthly datapoints for the average of all is depicted also (see the variable mauve plot).
What do the mauve trend curve and mauve monthly datapoint plot reveal?
- For the average of the world's longest and most complete sea level records, there has been relatively small variation in sea level trends calculated from the moving 30-year periods.
- The greatest sea rise trend took place at the 30-year period ending December 1952 - a trend rise of 10.6 inches per century.
- The lowest trend happened in May 1977 - an increase of 4.1 inches per century.
- The 100-year trend, as of the end of 2013, was 9.5 inches per century for all 15 sites.
- For the 12 sites reporting records through December 2014, the rise trend was 9.1 inches per century.
Putting it into the human-caused 'climate change' context, this global mean of long-term sea level trend has clearly not been a function of the rapidly rising CO2 levels (see chart's plot of moving 360-month average of atmospheric CO2 levels).
In summary, the overall sea level rise trend has been rather unimpressive, and slightly meandering back and forth since the early 1940s, while CO2 levels have exhibited a seemingly exponential growth. At the end of 2014, the 30-year trend amounted to a 2.3 to 2.5 mm (9 to 10 inches) increase per year.
The chart also reveals the two outliers of the group: Stockholm and Galveston, Texas. They both show a distinct cycle of ups and downs with no obvious relation to CO2 levels. (Stockholm's gauge has recorded a declining sea level trend.....at -14.3 inches per century, as of the end of 2014.)
For the other 13 gauge sites, the chart only depicts the smoothed fitted trends of sea level rise using the 30-year periods. Each site's trend exhibits a slightly different cyclical pattern cycle from others but most stay within a fairly narrow range over the decades. (See monthly per century trends plotted without the smooth fitted curves.)
Finally, the chart's two dashed fitted curves, red and blue, represent opposite trend directions at the end of 2013 - they are San Francisco and Freemantle, Australia. These two sites would suggest that a unified, in-sync global sea level change is not a reality.
Conclusion:
The above chart from the 15 sites indicates a current per century trend of 2.2-2.5 mm/year increase in mean sea levels, with the 1950's having a peak trend of approximately 2.7 mm/year (0.11 inches/yr). The raw sea level records when averaged, from beginning to end for the 101 years of records, calculates to an average site increase of 2.05 mm/year (0.08 inches/yr).
The current rate of sea level rise is not unusual versus the late 1940's and early 50's, which is an era prior to the huge increase in consumer/industrial CO2 emissions. And certainly this chart shows ancient sea level increases that were multiple times larger and faster than those observed with our modern climate.
This adjacent sea level infographic from a 2015 study published in the Science journal confirms that sea levels were significantly higher in the pre-history than our current levels.
When comparing the ancient past with the modern 15-site gauge per century trend of the last 30 years, it would take some 2,500 years to reach the 6-meter higher sea levels recorded approximately 125,000 years ago at a much lower CO2 level.
And to reach a more modest 1-meter sea level increase would take approximately 400+ years, per today's sea level trends.
**(Infographic's explanation: Peak global mean temperature, atmospheric CO2, maximum global mean sea level (GMSL), and source(s) of meltwater. Light blue shading indicates uncertainty of GMSL maximum. Red pie charts over Greenland and Antarctica denote fraction (not location) of ice retreat.)
The modern climate alarmism fears of the soon-to-be flooding of coastal regions, which would unleash a horde of climate refugees, is entirely without scientific merit, per the modern dataset records and the expert research done on the pre-history sea levels and trends.
Additional sea level charts.
Notes: Excel was used to calculate and plot the moving sea level per century curves and fitted trends (Excel slope function produced trends based on moving 360-month periods for each month in the dataset; then converted to per century trends (inches) for each month). Excel also used to calculate averages and to sort dataset records to identify highest per century trends for each site. The smooth fitted trends are to the 6th order. The Key West, Florida dataset's first record was January 1913, thus all 15 site sea level calculations started at the same date; the first 30-year trend calculated occurred at the December 1942 dataset record - hence, the plotted trends in the top chart start with December 1942. PSMSL datasets were the source of all records used for the chart. Download raw sea level datasets in Excel spreadsheet for all 15 sites, from 1913 to 2014. The datasets chosen included those that had data at least through December 2013; had at least a 100 year record of monthly reporting; and, had at least a 90% reporting of all 1,012 months covering the 101 years. The 'youngest' dataset meeting the criteria, Key West, determined the 101-year span used.