Saturday, May 31, 2014

New paper finds global & Australian sea levels rising less than 8 inches per century

A new paper published in Earth-Science Reviews finds sea level trends in Australia agree closely with global average sea level rise from tide gauge data of 2 mm/yr [7.9 inches per century] during the period 1966 to 2009. The authors find 69% of the variance in sea level trends related to the natural El Nino Southern Oscillation [ENSO].

According to the authors,

"A generalized additive model of Australia’s two longest records (Fremantle and Sydney) reveals the presence of both linear and non-linear long-term sea-level trends, with both records showing larger rates of rise between 1920 and 1950, relatively stable mean sea levels between 1960 and 1990 and an increased rate of rise from the early 1990s."
Australia's two longest sea level records: Rate of sea level rise in Freemantle is slightly higher than peak in 1920's and slightly lower in Sydney than peak in ~1950


There has been significant progress in describing and understanding global-mean sea-level rise, but the regional departures from this global-mean rise are more poorly described and understood. Here, we present a comprehensive analysis of Australian sea-level data from the 1880s to the present, including an assessment of satellite-altimeter data since 1993. Sea levels around the Australian coast are well sampled from 1966 to the present. The first Empirical Orthogonal Function (EOF) of data from 16 sites around the coast explains 69% of the variance, and is closely related to the El Niño Southern Oscillation (ENSO), with the strongest influence on the northern and western coasts. Removing the variability in this EOF correlated with the Southern Oscillation Index reduces the differences in the trends between locations. After the influence of ENSO is removed and allowing for the impact of Glacial Isostatic Adjustment (GIA) and atmospheric pressure effects, Australian mean sea-level trends are close to global-mean trends from 1966 to 2010, including an increase in the rate of rise in the early 1990s. Since 1993, there is good agreement between trends calculated from tide-gauge records and altimetry data, with some notable exceptions, some of which are related to localised vertical-land motions. For the periods 1966 to 2009 and 1993 to 2009, the average trends of relative sea level around the coastline are 1.4 ± 0.3 mm yr- 1 and 4.5 ± 1.3 mm yr- 1, which become 1.6 ± 0.2 mm yr- 1 and 2.7 ± 0.6 mm yr- 1 after removal of the signal correlated with ENSO. After further correcting for GIA and changes in atmospheric pressure, the corresponding trends are 2.1 ± 0.2 mm yr- 1 and 3.1 ± 0.6 mm yr- 1, comparable with the global-average rise over the same periods of 2.0 ± 0.3 mm yr- 1 (from tide gauges) and 3.4 ± 0.4 mm yr- 1 (from satellite altimeters). Given that past changes in Australian sea level are similar to global-mean changes over the last 45 years, it is likely that future changes over the 21st century will be consistent with global changes. A generalized additive model of Australia’s two longest records (Fremantle and Sydney) reveals the presence of both linear and non-linear long-term sea-level trends, with both records showing larger rates of rise between 1920 and 1950, relatively stable mean sea levels between 1960 and 1990 and an increased rate of rise from the early 1990s.

3 comments:

  1. Awhile ago I spent some time on Western Australian sea level data with a possible intent of mangling claims made about Freemantle but I never published the result.

    A certain notorious person was being sloppy as usual, trying it on. Freemantle was claimed to have the "usual" "accelerating" rise and to have the gauge on bedrock. That is highly mischievous but things are very complicated.

    The bedrock is actually a thin layer of broken limestone over many aquifiers, a coastal sedimentary mess. The Darling fault runs north-south to the east and separates a large crustal plate from the coastal region.

    There has been recent heavy pumping of a deep aquifer under the gauge, it then stopped. GPS etc. reference is poor but not far away are reference stations.

    Get the general idea? This comment would be pages if I wrote all as would a blog article, why I didn't.

    More or less after correction there is a straight line starting way back and yes the same as at any other competent station.

    Newlyn UK is one of the interesting ones, our forefathers had had enough of squabbling over sea level reference so they put a sodd'in great pin into the granite: there, that is the UK reference.

    Key twiddle, here we are, a post about Newlyn, link to Garden Pond where there is more and I'd forgotten, a plot of Freemantle.
    http://daedalearth.wordpress.com/2014/02/15/met-office-spurious-sea-level-claim/
    (if the links make it through the editor)

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  2. Sinking Fremantle: http://pindanpost.com/2012/12/19/not-so-scary-any-more-sea-levels/

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