This update analyses data which have become available since the last update in March 2015.
A datum shift which occurred when the Diego Garcia tide gauge was replaced in 2003 remains unresolved. This precludes an earlier record (1988–2000) from being combined with the post-2003 data.
The recent tide gauge record (15 years, 2003-2018) is still too short for reliable trend estimation of relative sea-level change.
The mean estimate of absolute sea-level rise from satellite altimetry for the Diego Garcia sea area is 4.21 mm yr-1 (26 years data, 1993 – 2018). 95% confidence limits for this trend estimate are 1.6-6.82 mm yr-1. On this basis, sea level at Diego Garcia has risen 10.5 cm over the last quarter century.
Between 1996 and December 2019 (24 years) there has been no detectable vertical land movement on Diego Garcia.
There is no evidence that extreme values at Diego Garcia (the highest spring tides) are increasing any faster than mean sea level.
At Diego Garcia, high tides in March 2012 that were observed to lead to flooding at the Donkey Gate on the western arm of the atoll have occurred 44 times since 2004. There is no evidence of a higher frequency of occurrence, nor that annual maximum spring-tide levels are increasing. (Note: These values differ from the 2015 update because the University of Hawaii Sea Level Center 're-calibrated' the Research Quality tide gauge time series in 2019).
A study in 2014 of regional sea-level change over the 20th Century suggests that Chagos sea level rose by about 6 mm yr-1 during the first half of the century (1901-1949) decreasing to 2 mm yr-1 in the latter half (1950-1999).
Richard Dunne
8 March 2020
A PDF of the full analysis is available to download: Chagos Sea Level March 2020 update
Page last updated: 1 December 2020