By Paul Homewood
I have long highlighted the fact sea level rise during the first part of the 20thC was just as high as now. In between, sea level rise slowed down considerably.
These sort of oscillations make it imperative that sea level trends are measured over much longer periods. Leading oceanographer, Bruce Douglas, often said that you needed to look at periods of 50 to 60 years.
In a new paper Parker and Ollier have analysed several large datasets of tidal gauge records, and conclude that sea levels have been oscillating about the same trend line during the last century and this century.
Long records of sea level show decadal and multi-decadal oscillations of synchronous and asynchronous phases, which cannot be detected in short-term records. Without incorporating these oscillations, it is impossible to make useful assessments of present global accelerations and reliable predictions of future changes of sea level. Furthermore, it is well known that local sea-level changes occur also because of local factors such as subsidence due to groundwater or oil extraction, or tectonic movements that may be either up or down.
Limited data from limited areas of study are, therefore, unsuitable for making predictions about the whole world sea level. Yet, people continue to make such predictions, often on an alarming scale. Here, we use one example to illustrate the problems associated with trying to make sea-level predictions based on a short record (25 years) in a limited region.
Linear and parabolic fittings of monthly average mean sea levels (MSL) of global as well as different local (United States Atlantic Coast, United States Pacific Coast) data sets of long tide gauge records.
It is clear from the analyses of the tide gauges of the “NOAA-120”, “US 39”, “PSMSL-162”, “Mitrovica-23”, “Holgate-9”, and “California-8” data sets and the United States Pacific and Atlantic coasts that the sea level has been oscillating about the same almost perfectly linear trend line all over the 20th century and the first 17 years of this century.
It is of paramount importance to discuss the proper way to assess the present acceleration of sea levels. This can not be done by focusing on the short-term upward oscillations in selected locations. The information from the tide gauges of the United States does not support any claim of rapidly changing ice mass in Greenland and Antarctica. The data only suggest the sea levels have been oscillating about the same trend line during the last century and this century.
This section of the paper is particularly revealing:
The loud divergence between sea-level reality and climate change theory—the climate models predict an accelerated sea-level rise driven by the anthropogenic CO2 emission—has been also evidenced in other works such as Boretti (2012a, b), Boretti and Watson (2012), Douglas (1992), Douglas and Peltier (2002), Fasullo et al. (2016), Jevrejeva et al. (2006), Holgate (2007), Houston and Dean (2011), Mörner 2010a, b, 2016), Mörner and Parker (2013), Scafetta (2014), Wenzel and Schröter (2010) and Wunsch et al. (2007) reporting on the recent lack of any detectable acceleration in the rate of sea-level rise. The minimum length requirement of 50–60 years to produce a realistic sea-level rate of rise is also discussed in other works such as Baart et al. (2012), Douglas (1995, 1997), Gervais (2016), Jevrejeva et al. (2008), Knudsen et al. (2011), Scafetta (2013a, b), Wenzel and Schröter (2014) and Woodworth (2011).
As an example of short-term measurement in a limited area, we consider the results of Davis and Vinogradova (2017). They consider time windows of only 25 years and only selected locations along the East Coast of North America. They neglect all other information in their selected locations and ignore results from other locations such as the West Coast of North America. Nevertheless, they draw global conclusions about sea level and the mass change in the ice of Greenland and Antarctica that per them has occurred since 1990.
Aim of this paper is to show that the information from the tide gauges of the USA and the rest of the world when considered globally and over time windows of not less than 80 years (but 120 years, or twice the quasi-60 years’ periodicity, work even better) does not support the notion of rapidly changing mass of ice in Greenland and Antarctica as claimed by Davis and Vinogradova (2017). The sea levels have been oscillating about a nearly perfectly linear trend since the start of the twentieth century with no sign of acceleration. There are only different phases of some oscillations moving from one location to another that do not represent any global acceleration.
In their Discussion, Parker and Ollier are even more scathing:
Davis and Vinogradova (2017) overrate the positive acceleration which they claim occurred after 1990 in one location by using a parabolic fitting of only 25 years of positive monthly average mean sea-level oscillations about the 60 years’ linear trend. They claim there was an acceleration of up to 0.3 mm/year2 after 1990. That is two orders of magnitude larger than the legitimate values. It is nothing but deceptive to infer global acceleration trends from short records while ignoring additional information from same tide gauges or tide gauges in other locations.
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November 1, 2017 at 06:15AM