Acceleration in mean sea level

Since 2011 Phil Watson of the Office of Environment and Heritage, NSW, has been analysing data from various tide gauges around the world for trends in mean sea level (MSL). He is continuing to publish his results in the Journal of Coastal Research (JCR) as part of his PhD program at the School of Civil and Environmental Engineering, UNSW.

Phil’s first paper in JCR addressed the question of whether there is evidence yet of acceleration in MSL around mainland Australia (JCR, 27, 2011). More recently he has looked at data from USA and Europe (JCR, 2016, and vol. 33, 2017). The more recent work has involved the application of improved tools, specifically an analytical packaged titled “msltrend” which is designed to enhance estimates of trend, real-time velocity, and acceleration in the relative MSL signal derived from long annual average ocean water level time series. Key findings are at the 95% confidence level.

This research is in the context of the use of MSL as an indicator of climate change. Models used to project climate change are forecasting that the current global average of MSL rise will climb from around 3 mm/y to a range of 10-20 mm/y by 2100. Such projections are fundamental to the assessment of shoreline change and coastal inundation in areas likely to be adversely affected in the future. To reach these higher rates of MSL rise it is important to apply different tools to evaluate the great mass of data from tide gauges to see if acceleration has commenced.

Phil has concluded from his inspection of tidal records of many sites in the USA and Europe that “no consistent or compelling evidence (yet) exists that recent rates of rise are higher or abnormal in the context of the historical records available across Europe, nor is there any evidence that geocentric rates of rise are above the global average” (JCR, 33, page 23). He notes that while the accelerated climate change influence is not yet statistically evident, “it is highly likely that such changes will take at least 15 to 20 years to manifest in the network of tide gauge records examined within this study” (JCR, 33, page 36).

I would like to commend Phil for his thorough analysis of this very important global question. His work adds to the enormous volume of research into sea level change. It is one of the key factors in driving shoreline dynamics. However, there are other factors operating at regional and local levels that influence coastal processes. Phil has made it clear that continued observations at many locations in the years ahead are vital in assessing sea level trends, but these observations must be made in the context of other coastal processes in order to provide the best advice to planners, managers and communities of possible future impacts of climate change.