“Ah, but I may as well try and catch the wind.” (Donovan, 1973)
By Dr. John Happs
In reality there is no such thing as a universal measure of sea level because there is no fixed datum against which measured levels can be compared. Similarly, the term “Global Average Sea Level” is simply meaningless and claims that sea level is rising at an unprecedented rate worldwide are questionable, if not deliberately alarmist.
The average depth of the world’s oceans is around 4,000 metres and for anyone to claim they know that global sea level has changed by 2 or 3 cm over the last few years requires pure imagination, especially in light of the many factors that influence relative sea level.
The array of factors that influence sea level measurements at any particular time and place include:
- Prevailing winds
- Ocean temperatures and salinity
- Natural climate oscillations
- Atmospheric pressure
- Gravitational forces
- Movement of land masses
There is no empirical evidence linking current miniscule levels of atmospheric carbon dioxide (CO2) to any variations in the above factors.
1. Prevailing winds:
Prevailing winds such as the Northeast Trades between North America and the Philippines or the Southeast Trades blowing between South America and Australia will lead to relative sea level rise on the western side of the Pacific Ocean (including Australia).
Wind speed and direction influence water levels in lakes as well as oceans. For instance, Lake Winnipeg levels can be 2 metres higher in the southern end when a strong north-westerly wind blows constantly for 2-3 days.
Ocean temperatures vary significantly between the equator and polar-regions. This produces fluctuating sea levels as water expands and contracts with temperature change. Warm currents such as the Gulf Stream and the Leeuwin Current and cool currents such as the West Australian current and Peru Current influence water temperatures and relative sea levels.
The sun is a variable star and, as solar activity varies, so can ocean temperature and relative sea level. As Dr. Nir Shaviv and Dr. Henrik Svensmark observe:
“Solar activity varies over time. A major variation is roughly eleven years or more, which clearly affects climate. This principle had been generally known – but in 2008 I was able to quantify it by using sea level data. When the sun is more active, there is a rise in sea level here on Earth. Higher temperature makes water expand. When the sun is less active, temperature goes down and the sea level falls – the correlation is clear as day.”
The salinity of seawater:
The salinity or salt content of seawater varies from place to place and this difference leads to different water densities and this impacts relative sea levels. In the Baltic Sea for instance, salinity is high at the entrance and lowest at the northern end with a 20 cm sea level difference.
Rivers flowing into the ocean and rainfall also have a localised influence on relative sea levels when these are measured at the point of river/rainfall input.
Natural Climate Oscillations:
Natural climate oscillations such as the Pacific Decadal Oscillation and the Atlantic Multi-decadal Oscillation cause variations in terrestrial temperatures and relative sea levels.
Atmospheric pressure due to local and regional weather conditions is constantly changing and sea level changes accordingly. High pressure systems depress sea level and force water down and out to other regions.
An increase in air pressure of 1 hPa will lower water level by 1 cm.
Conversely, low pressure systems cause sea level to rise and very low pressure systems, such as those created by hurricanes, can lead to significant sea level rise, tidal surges and flooding when hurricanes hit the coast.
Atmospheric pressure can vary between 950 and 1,050 hPa throughout the year, giving a natural sea level fluctuation of around 100 cm.
Measurements from orbiting spacecraft show that gravitational differences exist within the Earth’s crust, beneath the oceans.Such differences lead to changes in sea level at those locations.
Other gravitational forces act on the oceans as they respond to the sun and moon and their positions relative to the Earth.The sun-earth distance varies over time and this influences relative sea levels and the strength of tidal flows.
Movement of Land Masses:
Ice sheets covered much of North America and Europe during the last glacial maximum around 20,000 years ago. When those ice sheets melted, once-depressed land masses started to recover albeit slowly and unevenly. This process is called isostatic rebound.
Relative sea levels inevitably differ with considerable variation from place to place as a result of this uneven uplift of land.For instance, the British Isles is rebounding differently in different places such that some parts of Scotland are rising relative to sea level whilst some parts of the south of England appear to be sinking relative to sea level. This results in significantly different readings of sea level at different tidal gauges.
More than 20,000 years ago the Laurentide ice sheet covered much of North America to a depth of several kilometres. This massive ice sheet depressed the land. Again, as the ice melted, the land rebounded unevenly with the coastline having uplifted several hundred metres in some places.
The same process occurred across Scandanavia where relative sea level falls, measured at different sites, give different readings.
The Scandanavian Bomarsund sea level gauge is arguably the oldest in existence and is now well above the high-water line because of post-glacial land uplift.
Tectonic activity is also most effective in changing relative sea level measurements when land masses move up or down in a relatively short period of time. Tidal records for Japan illustrate this effect where relative sea level rose between 1906 and 1950 before falling for 15 years and then rising again:
Interestingly, tidal gauges in Oshoro, Waijima and Hamada show no indication of sea level rise.
Continental drift and the subduction of land at plate boundaries is a significant influence on relative sea level as is the changing geometry of ocean basins. Both depth and shape of basins change in response to tectonic activity.
There are other factors that influence relative sea level such as the continual extraction of groundwater. This can lead to local subsidenceand relative sea level rise. Groundwater depletion is common around the world and research shows that a high percentage of reports about sea level rise can be attributed to water extraction from underground aquifers.
Groundwater depletion for irrigation, industry and drinking water has a significant impact on localised relative sea levels in China, the US, India and Pakistan. Much of this water eventually ends up in the ocean and, compounded with land subsidence, can actually show an “apparent” sea level rise.
Where coastal settlements have been established on reclaimed land, subsidence and relative sea level rise is to be expected. Coastlines are rarely stable for long periods and they can be classified as erosional, depositional or (temporarily) stable. Parts of the east coast of England have seen whole settlements lost to the North Sea as a result of coastal erosion.
The town of Dunwich is now about 1 km offshore, joining other submerged towns such as Kilnsea and Eccles. In his book Men of Dunwich, Rowland Parker reported the loss as:
“Eight hundred houses… a dozen abodes of prayer and worship, windmills, workshops, taverns, shops, storehouses, ships.”
There are many settlements around the world that are now under water as a result of coastal erosion, including Kekova in Turkey; Port Royal in Jamaica; Alexandria in Egypt; Mahabalipuram in India and Tybrind Vig in Denmark.
Conversely, coastal accretion has resulted in settlements, once on the coast, now being located well inland. For instance, the ancient harbour city of Ephesus in Turkey was established in the 10th Century BC on the Aegean coast. Today, it is now 8 km inland.
As some shorelines erode, others are stable or building up, as Luijendijk et al. (2018) report:
“Analysis of the satellite derived shoreline data indicates that 24% of the world’s sandy beaches are eroding at rates exceeding 0.5 m/yr while 28% are accreting and 48% are stable.”
The many factors influencing relative sea level explain why there is a great deal of “sea level noise” and there are now more than 70 peer-reviewed, published papers that point to reported sea level change as being indistinguishable from such “noise.”
It is not surprising then that the IPCC and sea level alarmists have been unable to provide empirical evidence to support their predictions about carbon dioxide emissions and dangerous global warming-driven sea level rise.
The many factors influencing relative sea level serve to explain why there are a number of studies that point to sea level rising at less than 1 mm per year.
The many factors influencing relative sea level also serve to explain why there are a number of studies that show falling sea levels.
A study of the world’s best tide gauges, with more than 100 years of data, show an average 0.34 mm per year rise.
The many factors influencing relative sea level also serve to explain why there are a number of studies that show no anthropogenic signal in any sea level rise.
In addition to the many conflicting studies, there is a lack of evidence for alarm over unusual sea level rise but this didn’t deter the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (5AR) from stating:
“It is very likely that the rate of global mean sea level rise during the 21st century will exceed the rate observed during 1971-2010 for all Representative Concentration Pathway (RCP) scenarios due to increases in ocean warming and loss of mass from glaciers and ice sheets.”
The IPCC’s more alarmist prediction is at odds with results from many studies, leading Idso et al. to conclude that:
“Sea-level rise is a research area that has recently come to be dominated by computer models. Whereas researchers working with datasets built from long-term coastal tide gauges typically report a slow linear rate of sea-level rise, computer modelers assume a significant anthropogenic forcing and tune their models to find or predict an acceleration of the rate of rise.”
One might think that in the Netherlands, where much of their land is below sea level, the authorities would be most concerned about dramatic claims of rising sea levels. This is not the case.
Dr. Wilco Hazeleger, senior scientist at the Royal Netherlands Meteorological Institute (KNMI) commented:
“In the past century the sea level has risen twenty centimeters. There is no evidence for accelerated sea-level rise. It is my opinion that there is no need for drastic measures. It is wise to adopt a flexible, step-by-step adaptation strategy. By all means, let us not respond precipitously.”
Dr. Hendrik Tennekes, former Director of Research at the Royal Netherlands Meteorological Institute and expert in scientific modelling commented on global warming and sea level alarmism, saying:
“The blind adherence to the harebrained idea that climate models can generate ‘realistic’ simulations of climate is the principal reason why I remain a climate skeptic.”
Perhaps former CSIRO Principal Research Scientist Dr. Colin Barton, best sums up the sea level problem:
“I doubt if anyone who is not an earth scientist specialising in sea level changes would have any idea that it is nearly impossible to measure global sea level changes over centuries with an accuracy outside error limits.”
As Charles Manski said:
“If you want people to believe what you doknow, you need to be up front about what you don’tknow.”
Dr. John Happs M.Sc.1st Class; D.Phil. John has an academic background in the geosciences with special interests in climate, and paleoclimate. He has been a science educator at several universities in Australia and overseas and was President of the Western Australian Skeptics for 25 years.