What Is The Mean Sea Level And What Is Its Significance?

Tidal markers measure the incoming tides.
Tidal markers measure the incoming tides.

The mean sea level is a scientific term that is used to describe the average height of the oceans around the world. This average is determined by using the measurements of less active water, otherwise known as still or calm water, to avoid any possible increases due to waves or wind. Several industries, particularly those geared toward aviation and ocean navigation, rely on the mean sea level measurement in order to carry out their tasks. On aircrafts, for example, pilots utilize the mean sea level by subtracting the altitude on land from it to determine flight elevation and appropriate cabin pressure. Additionally, cartographers also rely on mean sea level measurements to produce accurate maps of the world, which are then used by ship captains.

The measurement of mean sea level is constantly changing as the result of a number of factors. The correlation between these factors and these measurements gives scientists a clearer understanding of why certain changes occur in the climate and environment. Geologists have also been working to determine the measurement of mean sea levels over a wide range of past geological eras as well. This information is important because by comparing data from previous time periods to data from current times, scientists are able to make informed estimates about what future sea levels may look like.

Measuring The Mean Sea Level

As previously mentioned, the mean sea level is determined by factoring out movements caused by waves and wind as these factors would significantly increase the result. To obtain accurate measurements, scientists use a special tool known as a tide gauge. Tide gauges come in many different forms, but one of the most common looks like a plastic tube. Special sensors are located inside of this tube, which is open at one end to let in water for the sensor to read. This tool is also used to transmit early tsunami warnings. Scientists compare the collected data to information from other sources and average the results over a specific time frame.

Changes In The Mean Sea Level

Because the ocean is constantly moving, the mean sea level is also constantly changing. Most of these changes are the result of short-term factors. Tectonic plate movement, atmospheric pressure, and even changing tides may result in short-term changes to the mean sea level. In this case, short-term is defined as anywhere from just a few minutes to just over a year.

Despite these short-term changes, however, researchers have been able to identify some trends in measurements over a long period of time. The majority of scientists agree that the oceans have been rising at an average rate of around one-tenth of an inch every year over the last century. In the last two decades, however, the average annual increase has been 0.13 inches. Some of the principal causes of rising sea levels are melting glaciers, eroding shorelines, and increasing temperatures in the water. As the ocean absorbs the increasing temperatures above water, its own temperature increases. Hotter waters cause thermal expansion in the top layer of the ocean. The overall increase in temperature is the result of human activity, like burning fossil fuels, that releases large quantities of greenhouse gases into the atmosphere.

Will The Sea Level Continue To Rise?

Although the mean sea level rise over the last century has remained relatively low, many researchers are worried that the average will increase exponentially in the coming years. These theories suggest that global climate change is occurring faster than previously believed. Because of the complexities behind climate patterns, calculating if the mean sea level will continue to rise is difficult. In fact, the global scientific community still has not reached a consensus on the expected growth of sea levels. Some scientists, for example, hypothesize that for every increase of 33.8° Fahrenheit, the oceans will rise by approximately 7.54 feet. Yet another group of researchers predicts that the mean sea level will increase by 10 feet over the next 50 years. According to the UN Intergovernmental Panel on Climate Change, people can expect the ocean to rise anywhere from 11 to 38 inches by the year 2100. All of these predictions mean that many coastal environments and communities around the world will be wiped out by the end of the century.

Effects Of Rising Mean Sea Level

The fact that the mean sea level is rising has significant consequences around the world. Generally speaking, researchers tend to classify these consequences into 5 categories: increased water tables, higher levels of salinity, flooding, erosion, and storm damage. Coastal regions around the world are the most affected by the increasing sea levels.

Entire ecosystems and habitats are destroyed as flooding and erosion tear through the land, which results in the loss of biodiversity in some of the most biodiverse regions around the world. This loss of species creates a ripple effect that goes on to negatively affect species in other habitats as well. Fish, seabirds, and marine turtles are just a few examples of animals that will be left without breeding grounds, shelter, and food. Additionally, the increased salinity in the water on land will leave many plants unable to survive. As these plants die, the shorelines become even more vulnerable to erosion.

Additionally, a large percentage of the global human population live in coastal areas, putting them at risk of damages from flooding. As the mean sea level increases, severe storms are able to make their way further inland, which causes greater damage than recorded in previous years. In many cases, people have already been forced from their homes. This displacement is particularly true for individuals living on small, low-lying islands. These individuals are referred to as climate change refugees and some governments are considering offering them visas. Not only are humans affected by increasing sea levels, but also by increasing salinity of freshwater supplies. The encroaching seawater makes its way into groundwater and aquifers. These aquifers are important sources of freshwater for humans and used for both drinking and farming. The absence of freshwater makes regions unsuitable for human habitation and for the pursuit of agriculture. A decrease in agricultural production means a food shortage for humans all over the world.


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