Azara Blog: Global sea levels rise possibly accelerating

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Date published: 2006/01/27

The BBC says:

Global sea levels could rise by about 30cm during this century if current trends continue, a study warns.

Australian researchers found that sea levels rose by 19.5cm between 1870 and 2004, with accelerated rates in the final 50 years of that period.

The research, published in the journal Geophysical Research Letters, used data from tide gauges around the world.

The findings fit within predictions made by the Intergovernmental Panel on Climate Change (IPCC).

The IPCC's Third Assessment Report, published in 2001, projected that the global average sea level would rise by between 9 and 88cm between 1990 and 2100.

In an attempt to reduce the scale of uncertainty in this projection, the Australian researchers have analysed tidal records dating back to 1870.

The data was obtained from locations throughout the globe, although the number of tidal gauges increased and their locations changed over the 130-year period.

These records show that the sea level has risen, and suggest that the rate of rise is increasing.

Over the entire period from 1870 the average rate of rise was 1.44mm per year.

Over the 20th Century it averaged 1.7mm per year; while the figure for the period since 1950 is 1.75mm per year.

Although climate models predict that sea level rise should have accelerated, the scientists behind this study say they are the first to verify the trend using historical data.

If the acceleration continues at the current rate, the scientists warn that sea levels could rise during this century by between 28 and 34cm.

Let's see. 1.75mm per year from 1950 to 2000 and 1.7mm from 1900 to 2000 and 1.44mm from 1870 from 2004. So (with some simple arithmetic) 0.5-0.6mm from 1870 to 1900 and 1.65mm from 1900 to 1950. Now the difference between the figures of the first half and second half of the 20th century are not great (perhaps surprisingly). So the "acceleration" is almost all due to the low figure for 1870. Well this might be totally correct data, but it does rather ring alarm bells. But at the very least, it seems to give working figures for the current rate of sea level rise. If the rise held constant at the second half of the 20th century figure (and not many people would believe that) then that would be another 17.5cm by 2100, so if it really is accelerating then the quoted range of 28 to 34cm seems reasonable.

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