Nearly Half Of 53 Tidal Gauges Show Negative Sea-Level Rise

The West Coast of North America has 20 long-term (90+ years) tide gauges measuring relative sea-level changes.

The East Coast has 33. Of the 53 total tide gauges, 45% (24) are negatively accelerating, 14 document falling sea levels, and just 11 have sea levels rising more than 3 mm/yr.

Image Source: Boretti, 2019

A cooling/non-warming North America

A few months ago, Gan et al. (2019) reported that the North American continent as a whole (180-0°, 15-60°N) “is one of the major cooling centers” in the Northern Hemisphere, with temperatures dropping after 1998 and no significant net change since the early 1980s apparent.

Image Source: Gan et al. (2019)

The contiguous United States has even undergone an overall cooling or non-warming trend – especially on the Eastern half – since 1900 (Partridge et al., 2018).

Image Source: Partridge et al., 2018

Image Source: Partridge et al., 2018

U.S. East Coast has been expanding, not shrinking, since 1960

A few months ago Armstrong and Lazarus (2019) indicated “trends in recent rates of shoreline change along the U.S. Atlantic Coast reflect an especially puzzling increase in accretion, not erosion.”

From 1830 to 1956, shorelines eroded at the rapid rate of -55 cm per year on average. Since 1960, the U.S. Atlantic coast has been expanding (accretion) at a rate of +5 cm per year.

Image Source: Armstrong and Lazarus, 2019

Twelve of 15 Florida Bay islands have also been expanding in size since the 1950s (Zhai et al., 2019).

Image Source: Zhai et al., 2019

New study: 45% of 53 long-term North America tide gauges show negative acceleration

A new paper (Boretti, 2019) utilizes 90+ years of continuous tide gauge data from the Permanent Service for Mean Sea Level (PSMSL) to record the sea-level trends from the West Coast (20) and East Coast (33) of North America.

Boretti finds the average sea-level change for the 20 West Coast tide gauges amounts to -0.38 mm/yr, whereas the average sea level rise rate is +2.22 mm/yr for the 33 East Coast gauges.

Much of the relative differences between the two coasts can be explained by land subsidence (sinking) or uplift (rising).

“Nearly the entire East Coast of the United States, from Massachusetts and parts of Maine to Florida, is known to be affected by subsidence [6–10]. Subsidence is much stronger along the East Coast of the United States and significant only in Southern California along the West Coast, and it increased in intensity since the mid-1900s.”

Image Source: Boretti, 2019

Of the 53 total tide gauges on North America’s East and West coasts, 45% (24) are negatively accelerating, 14 document falling sea levels, and just 11 have sea levels rising more than +3 mm/yr.

The overall acceleration for both the East and West coasts amounts to just +0.0028 mm/yr² and +0.0012 mm/yr², respectively, when using the late 1800s and early 1900s as the starting years.

An analysis by Houston and Dean (2011) showed that when the sea level trend begins in 1930, the U.S. coasts as a whole actually decelerated overall (-0.013 mm/yr²) during 1930-2007.

These modest trends would not appear to support the contention that modern sea-level changes in this region are rising at alarming rates.

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