Updated on 15 Feb. 2023
Japan Meteorological Agency
A trend of sea level rise has been observed in Japanese coastal areas since the 1980s, but no long-term trend of sea level rise is seen for the period from 1906 to 2022. Variations with 10- to 20-year periods (near-10-year variations) and over-50-year periods are seen for the period from 1906 to 2022.
Time-series representation of annual mean sea level values (1906 – 2022)
The 1991 – 2020 average is used as the normal.
Annual sea level anomaly time series (comma-separated value file: 3 KB)
The graph indicates annual mean sea level anomalies for each year averaged among the four tide gauge stations shown in the map on the left below for the period from 1906 to 1959, and among the four regions shown in the map on the right below for the period from 1960 onward. The solid blue line represents the five-year running mean of annual sea level anomalies averaged among the four stations, while the solid red line represents the corresponding value for the four regions. The dashed blue line represents the value at the four stations for the same period shown by the solid red line (from 1960 onward) for reference.
Locations of tide gauge stations
Tide gauge stations assessed as being affected to a lesser extent by crustal movement are selected for monitoring of sea levels.
The four stations shown on the map on the left were selected for the period from 1906 to 1959, and the 16 on the right are for the period from 1960 onward.
These 16 stations are divided into four regions (I – IV) for the latter period.
The stations at Oshoro, Kashiwazaki, Wajima and Hosojima belong to the Geospatial Information Authority of Japan.
Sea level data for the Tokyo station are available from 1968 onward.
Sea level data from 2011 to 2022 at Hakodate, Fukaura, Kashiwazaki, Tokyo and Hachinohe are not used due to the influence of the 2011 Great East Japan Earthquake.
Time-series representation of annual mean sea level anomalies (1960 – 2022) for the four regions
Four-region annual sea level anomaly time series (comma-separated value file: 2 KB)
Rate of sea level rise in each region (mm/year)
| I | II | III | IV | Average | Global mean (IPCC AR6) |
|
|---|---|---|---|---|---|---|
| 1960 – 2022 | 1.2 [1.0 – 1.4] | 1.0 [0.5 – 1.5] | 1.2 [0.9 – 1.6] | 2.6 [2.3 – 2.9] | 1.5 [1.2 – 1.8] | |
| 1971 – 2006 | 1.3 [0.8 – 1.8] | * | * | 2.2 [1.6 – 2.7] | 0.9 [0.3 – 1.5] | 1.9 [0.8 – 2.9] |
| 2006 – 2018 | * | 4.9 [1.4 – 8.4] | * | 4.0 [1.6 – 6.3] | 2.9 [0.8 – 5.0] | 3.7 [3.2 – 4.2] |
A trend of sea level rise has been observed in Japanese coastal areas since the 1980s, but no long-term trend of rise is seen for the period from 1906 to 2022. Variations with 10- to 20-year periods (near-10-year variations) and over-50-year periods are seen for the period from 1906 to 2022. The annual mean sea level around Japan in 2022 was 63 mm higher than the normal (i.e., the 1991 – 2020 average), making it the second highest since 1906.
From 1960 to 2022, the trend of sea level increase in Region IV was larger than that of the other regions.
Analysis has shown that the near-10-year variations observed are caused by changes in the strength and meridional movement of westerlies over the North Pacific and the high sea level around 1950 was induced by a weakening of the Aleutian low (Sasaki et al., 2017) . Sea level variation data correlate well with those showing changes in subsurface seawater temperatures, especially around the Nansei Islands.
The IPCC Sixth Assessment Report(AR6) on the physical science basis of climate change concluded: "Total global mean sea level (GMSL) rise for the period from 1901 to 2018 of 0.20 [0.15 to 0.25] m. The average rate of sea level rise was 1.3 [0.6 to 2.1] mm/year between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm/year between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm/year between 2006 and 2018(high confidence). Human influence was very likely the main driver of these increase since at least 1971. In contrast to the globally averaged rate noted in the IPCC report, sea levels in Japanese coastal areas showed no significant rise from 1906 to 2018; the rate of rise around the country was 2.9 [0.8 to 5.0] mm/year from 2006 to 2018. These figures are comparable to those observed for the global average in recent years.
However, the extent to which global warming has contributed to sea level change along the Japanese coast remains unclear due to the involvement of various other factors such as near-10-year variations. In order to determine the long-term trend of sea level rise caused by global warming, continuous monitoring is required.
The values in square brackets show the 90% uncertainty range.