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Scientists have long since established that due to human activity the average temperature of the planet is rising, which causes a concurrent rise in sea levels. While some may argue that rising sea levels are a minor concern, future projections concerning global temperatures and sea levels indicate that even a small amount of warming can lead to widespread destruction in coastal areas, including the sites of many of the world’s major cities. In order to minimise the potential damage, some states and municipalities have already put plans in motion to mitigate the most severe effects of rising sea levels. However, many scientists and politicians have warned that without drastic change, many coastal areas will be effectively uninhabitable by the end of the 21st century.
Water covers about 71 percent of the earth’s surface. At present, 97 per cent of water is found in the oceans, with the majority of the remaining 3 per cent contained in glaciers and polar ice. Only a tiny fraction of the planet’s water is found in rivers, lakes and underground aquifers. Throughout history, these proportions have fluctuated with the earth’s climate: as temperatures fall, more ice is locked into glaciers and ice sheets, and sea levels fall. The opposite is true when temperatures rise: glaciers and polar ice melt, releasing water into the oceans and causing sea levels to rise. The most recent glacial period reached its peak about 26,500 years ago. At that time, some 26 million square kilometres of ice covered large parts of every continent on Earth, and the global climate was colder and drier. As so much of the planet’s water was enclosed in ice, sea level was more than 100 metres lower than it is today, with more land accessible to humans than nowadays. When the world slowly warmed over the following millennia, those lands were flooded by rising sea levels and eventually disappeared beneath the ocean’s surface.
If the rise and fall of sea levels is a natural occurrence, what makes it different now? Since 1900, the average sea level has risen by nearly 20 centimetres, whereas in the previous 2,000 years sea levels were almost static. Additionally, the rate at which these changes occur is getting faster: from around 1.5 millimetres a year between 1900 and 1990, to on average 3.2 millimetres per year since 1993, and measurements show that this trend is set to continue.
Scientists agree that climate change is principally driven by human activity, and in particular by the consumption of fossil fuels—coal, oil and natural gas—that has risen exponentially over the last hundred years. When burned, these fuels release carbon dioxide, which helps to trap heat in the atmosphere, creating the so-called ‘greenhouse effect’. Due to the higher global temperatures thus caused, glaciers and ice sheets melt at an increased rate. Large ice sheets and glaciers melt in three ways: from the top because of warmer air, from the sides as parts break off, and from below due to a higher sea temperature. The meltwater thereby produced increases the total volume of water in the earth’s oceans, causing a rise in sea levels. It has been established that one-third of the rise in sea level to date is due to the melting of polar ice, and one-third is due to the melting of glaciers and other land-based ice. The remaining third is attributed to thermal expansion: as temperatures rise, the water in the oceans becomes less dense.
According to climate research, for every 1 degree Celsius of warming, sea levels will rise by around 2.3 metres. Scientists expect that if carbon dioxide emissions continue at current rates, temperatures will rise by approximately 4 degrees Celsius by the year 2100. To put this in perspective, the concomitant rise in sea levels will flood coastal land which is presently home to over 400 million people. Coastlines will be reshaped and the water will flood dry areas and erode beaches, cliffs and dunes along shorelines. Additionally, warmer oceans will generate more dangerous and powerful storms—including hurricanes and typhoons—which are projected to become around 10 per cent stronger on average over the next hundred years. Stronger storms can reach further inland, possibly causing flooding and damage even far from coastlines.
Rising sea levels are inevitable; the process cannot be stopped, so humans must find a way to adapt. Reducing our consumption of fossil fuels can slow the rate of global warming, giving future generations more time to adapt to changing conditions. A partial solution to the loss of habitable land near the coast is for people to live further inland; however, it is not practical to simply abandon coastal cities, which include some of the most populous urban areas in the world today. Another option is to protect cities from flooding by building artificial defences. Some low-lying countries—such as the Netherlands—already have experience in fighting back against the encroachment of the tides. There, man-made barriers effectively turn the part of the sea into a lake, protecting the land behind from sea level changes as well as from flooding due to storms. Such innovations could be useful for areas such as Shanghai, Florida, New York, Osaka, and large parts of South East Asia. Building sea walls will not suffice; large buildings need floodgates, tidal valves can be installed in drainpipes to prevent water from flowing the wrong way, and river walls can prevent flooding when water levels rise. The construction of new buildings in coastal areas may be supported by poles or floating foundations.