Doomed Planet

Sea levels ignore government forecasts

Have you got a beach house, for holidays or residence? If so, you have two big things to worry about.

First, will sea-level rises due to global warming undermine the foundations? Second, will your local council pass some regulation based on their sea-level projections, that will shred the value of your beach house?

It was only last June that the coalition government in Victoria put out helpful and “pragmatic” new maps of the coastline to give councils and planning authorities a better idea of projected coastal inundations: a Coastal Hazard Guide.[i] The press release was accompanied by an adult version of an elephant stamp: “Policy Implemented”.

Underpinning the guide is a Fact Sheet from the Victorian Department of Sustainability and Environment, saying that since 1993, satellites show that sea level rise has accelerated to 3.1mm a year, compared with 1.7mm through the 20th century.[ii]

The Fact Sheet says that although the Intergovernmental Panel on Climate Change in its 2007 report forecast sea level rises of 20-80cm by 2095, scientific studies since then have upped the estimates to 50-200cm – and a study by Rahmstorf (2012)[iii] was even more pessimistic.

From my eye-balling of the accompanying chart in the Fact Sheet, this study shows a typical mid-point forecast of about 120cm rise, and worst-cases of 150cm-220cm.

Heaven knows what other State governments are putting about on this subject.

Well, we now have a study by Associate Professor Alberto Boretti of Ballarat University, published in the peer-reviewed Coastal Engineering: “Short term comparison of climate model predictions and satellite altimeter measurements of sea levels”.[iv] Boretti says sea levels rises haven’t accelerated in the past 20 years, they’ve decelerated. Therefore those IPCC and other alarmist sea projections are most unlikely to be fulfilled.

Boretti is an M.Sc. (mechanical engineering) and Ph.D. (energy engineering) from the University of Florence. He has published or co-published 80 or so journal and conference papers. Unlike many academics, he has spent decades in industry on research and development, including as group leader on car engines at the FIAT Research Centre, Orbassano, Italy.

The Coastal Engineering journal’s editorial board is dominated by academics from Japanese universities (11 of 17 members) with others from places ranging from the US Army to the University of NSW.

Boretti cites the same Rahmstorf study in his preamble as does our Victorian Department of Environment, but he reminds us that four studies reaching precisely the opposite conclusion have also been published.[v] That is, those papers concluded that sea level rises are not accelerating.

This is hard to square with the Environment Department’s bland assertion that “The likely extent of sea level rise is becoming clearer as our understanding of the processes that contribute to sea level rise continue to improve.”[vi]

Boretti quotes the Australian Federal Government’s Climate Commission as warning that global warming could cause sea levels to jump higher than previously thought, by up to one metre. He also quotes the IPCC’s verdict that homes and livelihoods of “millions” of people worldwide in low-lying land are at risk.

Boretti’s study takes the best available sea level data sets: TOPEX and Jason, two 20-year series from satellite radar altimeters, via the University of Colorado. He uses simple statistical methods to work out if the data shows that sea levels rises are accelerating, stable or decelerating.

He found the average sea level rise (SLR) over the two latest decades was 3.1640mm/year.

The annual rise over the two decades is reducing by -0.11637mm/year, and the acceleration of rise is reducing at a rate of 0.078792mm/year.

To meet the IPCC’s prediction of a 100cm rise in sea level by 2100, the annual rise must be almost 11mm/year for the next 89 years, he says, compared with the recent actual rise of 3mm. But since even the current low rate of rise is dropping, the IPCC forecast is not so credible. He adds that never in the past 20 years has the posited 11mm/year rate ever been recorded. Indeed the recorded average rate is only fraction of what’s needed to generate the hypothesized 100cm end-of-century rise.

What he calls the “huge” deceleration over the past 10 years is “clearly the opposite of what is being predicted by the models. Even more interesting is the fact that from 1992 to 2005 there was an increase each year of the SLR. 2006 was the first year to show a reduction in the global SLR. 2010 is the second year to show a decrease in the SLR:

The average SLR over the last 5 years is also much smaller than the average rate of rise over the last 20 years. These already small SLR numbers are reducing, not exponentially increasing, and this is a consistent trend over the last 5 years.

The satellite-derived trends, he says, are “completely different” from the prediction of Rahmstorf in 2007 – which as I’ve noted is what the Victorian government’s coastal hazard policy relies on – and are consistent with the tide-gauge results of Wenzel & Schroeter.[vii]

Boretti concludes:

The assumption [of Rahmstorf] that SLR is proportional to the temperature rise, and that this temperature rise is proportional to the anthropogenic carbon dioxide emission, is certainly too simplistic to represent a reality where there are other driving forces that do need attention.

Note: The article by Boretti has been available online since November, 2011, but only got some real traction this month. Boretti two months ago had a second article published in Coastal Engineering, which is equally subversive of Australian governments’ policy underpinnings.[viii]

In this latest article, he noted that maps with 0.5, 0.8 and 1.1m sea level rises have been proposed for Sydney. But he finds that long term tide gauges worldwide, and Australian coastal levels including within the bay of Sydney, “do not show any sign of accelerating sea level rises at present”.

In fact, he says, long-term gauges show weak rises and no acceleration; satellites show more intense sea level rises but still no acceleration; and sea level rises of metres in the bays of Sydney are “not very likely to occur in the short term.”

Tony Thomas is a retired journalist.



[iii] Rahmstorf, S., 2010. A new view on sea level rise: has the IPCC underestimated the risk of sea level rise. Nature Reports Climate Change. doi:10.1038/climate.2010.29. Published online: 6 April.

[iv] Summarised at Original for USD35.95 at

[v] Holgate (2007) analysed nine long-series sea level records from 1903-2003 and found sea levels were rising faster in the early 1900s than in the later part of the century.

Wenzel & Schroeter (2010) found no statistically significant acceleration in sea level rise in the 1900-2006 period, based on tide gauges.

Wunsch (2007) using modelling, estimated sea level rise at only 1.6mm/year for 1993-2004.

Houston & Dean (2011) looked at 57 tide gauge records each covering 80 years, and found no acceleration, but instead a small average deceleration.

[vi] Op. cit., Fact Sheet, see 2

[vii] Op. cit., Wenzel, see 5

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