What actually is sea level? Sea level or ‘mean sea level’ as it is known, is the average height of the ocean’s surface between high and low tide. Changes in tides and wave conditions over time are averaged out to determine a ‘still water level’ that can be used to determine whether the sea level has changed or not. The important question that needs to be answered is- What causes a change in the sea level? Global warming is a burning issue, and it is also the main reason behind the increasing sea levels everywhere. As global temperatures rise, the oceans warm up slightly and expand, ice caps and glaciers melt, and more precipitation falls as rain instead of snow. Tide-gauge records dating back 100 years indicate a rise in global mean sea level that amounts to one to two inches every 25 years, and this level is continuously increasing. A continuous change in sea level because of any of the above listed reasons creates a great impact on animal and plant life, and the result is:
Extinction of certain species: Since the beginning of life on Earth 3.5 million years ago, scientists estimate there have been as many as 23 major extinction events. During the past 540 million years, there have been 5 major mass extinctions, primarily of marine plants and animals. The idea that sea level changes are the reason behind these extinctions has been around for 60 years, but till now the scientists have not been able to prove the disastrous impact caused by these changes. A research which appeared in the journal ‘Nature’ provides an interesting perspective on one of nature’s most pervasive mysteries. The research states that most of the major mass extinctions in the past have been associated with the draining of large shallows seas that once covered much of the present-day land surface.
Decrease in Earth’s population of various animal species: In order to survive, wildlife needs the availability of right temperature, fresh water, food sources and places to raise their young ones. A rise in sea level has impacted the survival of these animals to a great extent:
Polar Bears: Arctic’s top predator, the Polar Bear is affected both by the changing sea level and by the reduced stocks of its primary food, the seal. Polar bears use sea ice as a platform for hunting their prey and for resting. A reduction in sea ice which is a major reason for the changing sea level has made it extremely difficult for these polar bears to survive in their native place. They catch adult seals when they come up through the ice hole, but ice reduction has caused a reduction in the abundance of seals available for food. Global warming has melted large areas of frozen ice in the ocean, and the polar bears have to swim to long distances in search of food.
Sea turtles: Rising sea levels are making a great impact on the world’s sea turtles. Six turtles are already on the world’s endangered species list: green turtles, hawksbills, loggerheads, Kemp’s ridleys, Olive ridleys and leatherbacks. All female sea turtles come ashore at nesting beaches, dig nests in the sand, lay their eggs and then return to the sea. Erosion of nesting beaches caused by rising sea levels leads to an impact on the reproduction of sea turtles.
Corals: Rising sea level could lead to a temporary or long-term decline in the abundance and diversity of animals like corals, and corals form coral reefs. This phenomenon would result in the disappearance of abundant marine life that once congregated around these coral reefs. Warmer water has already caused coral bleaching in many parts of the world, and further loss of coral reefs would disrupt the food web that connects all the living creatures in the ocean.
Penguins: A steep decline in the population of penguins in Antarctica has been observed, and this has happened because of disappearing sea ice and a rising sea level over the past century. There are about 20 million breeding pairs of penguins in the Antarctic, and some species of penguins in Antarctica are declining, while some are not.
Shellfish: Factors like changes in salinity and rising sea level could decimate mangrove forests, leaving many fish, shellfish and other wildlife without a place to breed, feed or raise offspring.