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Rising seas: Let’s look at the numbers


Rising seas since 1880 added  21-24 centimeters (8-9 inches) to the global mean sea level.

About 9 centimeters of that sea-level rise occurred between 1993 and 2018.

Rising Seas
Sea Level Rise (NOAA)


Rising seas are the result of two primary contributing factors. NOAA data from 1993 to 2018 accounts for both of these factors. So, the nine-centimeter sea-level rise during this 25 year period resulted from the following contributions.

Thermal expansion accounted for 3.5 centimeters of sea-level rise.

Added water (mostly from ice melting) accounted for 5.5 centimeters of sea-level rise.

Thermal expansion is a surprise factor for some people, but remember that water expands as it warms up. More than 90 percent of the extra heat absorbed by planet earth over the past 50 years ended up in the oceans. When heat is absorbed then temperatures rise.

Rising Seas
Components of Sea Level Change (NOAA)


Rate matters. A steady rate assumption using the average sea-level rise per year between 1880 to 2006 underestimates the rise over the next century by at least 60 percent. 

The current rate of sea-level rise is 3.6 millimeters per year.

“The rate of sea-level rise is accelerating: it has more than doubled from 0.06 inches (1.4 millimeters) per year throughout most of the twentieth century to 0.14 inches (3.6 millimeters) per year from 2006–2015.” (NOAA)


Flooding comes in two colors: Disaster flooding from storms and then nuisance flooding (high-tide flooding). Hence, rising seas affect both types of flooding.

Nuisance flooding is now 9 times more likely in some coastal locations than it was in 1970. So, ten days of high-tide flooding in 1970, now translates into 90 days of nuisance flooding.

“In many locations along the U.S. coastline, high-tide flooding is now 300% to more than 900% more frequent than it was 50 years ago.” (NOAA)


Ocean warming dwarfs atmospheric warming (Source: ArcheanWeb) – https://archeanweb.com/2020/01/21/ocean-warming-dwarfs-atmospheric-warming/ Also:


Climate Change: Global Sea Level (By Rebecca Lindsey; NOAA) – https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level Also:

Feature Image: Farmacy under water Venice 2019 (By All About Venice) (Modified)  https://commons.wikimedia.org/wiki/File:Farmacy_under_water_Venice_2019.jpg  – Also: This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. – https://creativecommons.org/licenses/by-sa/4.0/deed.en

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.