By Tripti Chanda
The fear of rising sea levels has always been a nightmare that researchers have tried to make the general public aware of. The rate of rising levels are low and the impact is subtle enough for the people to be lulled into a sense of false optimism. The latest research on this subject, however, has shown that we were wrong about our estimate of the rate of rising levels itself. Not only are the levels rising but they are also accelerating.
The ‘old’ why
It is a known fact that the levels of our ocean bodies are steadily rising. The global mean sea level (GMSL) has risen by more than 7 cm since 1993, indicating a rate of about 3 mm every year, over a span of 25 years.
Originally, the main three reasons theorised for the rise were thermal expansion, melting of glaciers and polar ice caps, and the loss of ice from the ice sheets of Antarctica and Greenland. All these reasons can be traced down to a single root—global warming. As the water heats up due to global warming, it expands, increasing the volume occupied by it. The melting of the ice sheets and the polar ice caps can be explained by the same problem. The ice melted in the summer is not being compensated by the freezing done over the winter, as had usually happened before.
With a continuous increase in global warming itself, there has been a rise in the amount of heat in the atmosphere. This further accentuates the effects and causes a greater rise in the water levels.
The GMSL is different from the relative sea level trends. The normal surface of the oceans is not always level and changes according to its specific location, ocean currents, variations in the height of land and the cumulative effect of the weather on the land nearby. As a result, making accurate measurements of sea levels is a difficult task. Initially, core samples and tide gauge readings were used but these were not able to differentiate between the GMSL and the relative trends. This lead to readings which were not exactly dependable.
The ‘new’ why
The latest data that has been collected has been done using satellites. The satellite altimeter, that has been collecting this data for the past 25 years, has the advantage of having an enormous amount of data which can be studied to make calculated decisions regarding the future. This eliminates decadal variability. It has collected this data by sampling the open ocean, helping us differentiate between changes in terrestrial water storage and actual change in sea levels.
Previously, using these methods, we would get certain levels of increase in the rate of rising and then some unpredictable levels of decrease, which seemingly righted the GMSL. This happened because the samplings were affected by the weather conditions and natural disasters occurring nearby. The error in the data collected by the altimeter was verified after comparing it with the data collected by the tidal gauge. The data collected showed that after taking into consideration all the errors that were neglected in the previous methods, the error in the rate of increase was nearly 0.025 mm/year. This makes the rate of rising to be accelerating at a rate of nearly 0.084 ± 0.025 mm/year. If the future sea levels are calculated using this data, there is a rise by nearly 200%, as compared to the original predictions.
The satellite data has been carefully evaluated to examine the El Niño and La Niña effects (ENSO, or the El Niño Southern Oscillation) which affect the terrestrial water storage levels and the effect of natural disasters, like the major eruption of Mt Pinatubo in 1991 which caused a decrease in the GMSL.
Is the year 2100 ‘official’ doomsday?
It has been proven that the possibility of the rate of acceleration being less than zero is actually less than 1%. This projection shows that the water levels in the year 2100 would have risen by nearly 65 cm, which is more than the double of what would have been with a steady rate in place, as predicted earlier. Of this, 55% is predicted to be due to the thermal expansion of water. This would be enough to submerge most of the coastal cities. This would incur a huge loss in life and property as most of the coastal cities have high population density.
Even today, in most of the under-developed nations, the lower members of the society are exiled to the coastal regions and marginal areas where the incidence of floods and high tides is increasing.
Can it be reversed?
The human race has wrought a large amount of imbalance in the environment. No matter how much we deny it, this is causing and will continue to cause, harmful effect,s not only to humans but to the Earth in general.
The current century has seen more stringent methods of controlling global warming, but the effect of the steep increase in global warming during the previous century will take a long time to reverse. The developed nations have tried to get a handle on things while some of the developing ones have a plan of action. This would not only not have an immediate effect but would also only slow down the rate and not completely stop it in any way. There is very little active movement going on to reverse this damage and this has to be undertaken soon for fear of doing too little, too late. The most we can hope for at this moment is to stabilise the rate to ensure survival.
If the current predictions are correct, sea levels may continue to rise for quite a few centuries to come at a rate much higher, as compared to the current and the previous century. Even after extensive preventive measures undertaken by each person of the society, it is difficult to predict when exactly this rise would stop. Many experts have suggested survival training and flood response to be started as soon as possible in coastal areas, at the very least. Survival of floods would have to become mandatory training with dedicated rehabilitation centres and helplines required.
The next logical step
As the sea levels rise, the predictions for most of the coastal areas is bleak. From the coastal areas getting completely submerged to yearly floods in marginal areas, a huge dent in the world economy is expected due to a large loss of habitable land.
Though it seems dark looking ahead, the future may not be definitely so. This year, NASA will launch two additional satellite missions that will help in improving and confirming the predictions. The missions are called the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission and the Ice, Cloud and land Elevation Satellite-2 (ICESat-2). The study done till now has been proclaimed by some as only worthy of medium-confidence, depending on the empirical data. The year 2100 is still some time away, but it would do all of us good to remember that time and tide wait for none.
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