Sea rise slow down raises questions › News in Science (ABC Science)Posted: October 14, 2013
Friday, 22 July 2011
A recently published study on sea level rises in Australia and New Zealand has some questioning the effect of climate change on the oceans.
Phil Watson, a coastal researcher with the New South Wales Office of Environment and Heritage, analysed data from four tide gauges, located at Fremantle, Sydney, Newcastle and Auckland, collected as far back as 1897.
He notes in his study that various long-term factors such as changes in the Moon’s orbit, El Nino events and the Pacific Decadal Oscillation affect sea levels on a periodic basis. To remove these effects, the data was converted into a 20-year moving average.
“The 20-year moving average water level time series through to 2000 clearly depict relative water level changes that are increasing over time, though at a reducing rate,” writes Watson in his study which appeared in the Journal of Coastal Research.
He says the most reliable gauges, located at Fremantle and Auckland, show an increase in sea level of approximately 120 millimetres between 1920 and 2000, or 1.5 millimetres per year. But this increase is reducing at a rate of between 0.02 and 0.04 millimetres per year.
“This decelerating trend was also evident in the detailed analysis of 25 US tide gauge records longer than 80 years in length,” he writes.
“Further research is required to rationalise the difference between the acceleration trend evident in the global sea level time-series reconstructions and the relatively consistent deceleration trend evident in the long-term Australasian tide gauge records.”