Wednesday, 27 June 2012

Extending the record - Newcastle, NSW sea level

Newcastle, New South Wales, Australia has had a record number of tide gauges - five in total, but the latest (Newcastle V) had a shaky start. Installed in 1957, the NTC record shows just 5 months of data for 1957/8, with many gaps, and a very large data-free gap until 1966. Luckily Newcastle III was still in operation (until end 1988), so there's a long overlap.

Also lucky is that there's little significant difference between the two, with an average difference of just 0.6 mm over the last three years 1986-88, small enough to be ignored, and allowing a simple "join" at the end of 1988.

The trend line is pulled down by the large dips on the left; a better picture of the later trend is shown from 1949 onwards:

... where the 3-year (37 month centred) moving average straddles the trend line convincingly, and significantly shows an almost identical trend to the reliable part (1966-onwards) of the plot for gauge V, which is shown in my reference page for Australia:

The plot for Sydney in my previous post shows a slight dip over the decade from about 1938, but not as large as the double-dip for Newcastle, over two decades. That it wasn't due to simple disturbances of the gauge is shown by a plot of gauges I and III:

For now, that anomaly must remain a mystery. Perhaps it was due to disturbances caused by mining activity. However, from these long-term reconstructions, it should be clear that there's been no acceleration in sea level change during the latter half of the 20th century, nor in this century, despite what's claimed by the CSIRO and others.

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