The core samples, tide gauge records and, ultimately, satellite measurements show that over the last century, the Mean Sea Level (GMSL, for its acronym in English) increased between 10 and 20 centimeters. However, the annual rate of increase over the past 20 years has been 3.2 millimeters, roughly double the average rate of the previous 80 years.
Over the past century, the burning of fossil fuels and other human and natural activities released into the atmosphere huge amounts of heat-trapping gases. These emissions have caused the surface temperature of the Earth has increased and that the oceans have absorbed about 80 some of this additional heat.
Rising sea levels is linked to three main factors, all of them induced by the current climate change:
Thermal expansion: When water is heated, it expands. About half of the increase in sea level that occurred over the past century is attributable to the fact that the oceans, when heated, take up more space.
The melting of glaciers and ice caps: Large ice formations, such as glaciers and ice caps, naturally melts in summer. But in winter precipitation as snow, composed mostly of evaporated seawater, usually sufficient to offset the thaw. However, the persistent high temperatures recorded recently because of global warming, are responsible for the amount of melting ice in summer has increased and snowfall have decreased because the winters and springs are delayed forward. This imbalance generates a significant net increase in runoff against evaporation from the oceans, causing sea level to rise.
Loss of ice in Greenland and West Antarctica: As with the glaciers and ice caps, increased heat is causing the massive ice sheets covering Greenland and Antarctica melt at an accelerated pace. Also, scientists believe the sweet water generated by melting at the surface and sea water beneath its surface are leaking beneath the ice sheets of Greenland and West Antarctica, lubricating the ice streams and causing these slide faster into the sea. Moreover, rising temperatures are causing the huge ice shelves attached to Antarctica are melting from the base, to weaken and break off.
When sea level rises quickly, as it has been doing in recent times, even a small increase can have devastating consequences on coastal habitats. Seawater penetrates into increasingly remote areas of the coast, which can lead to catastrophic consequences such as erosion, flooding of wetlands, pollution of groundwater and agricultural land, and the loss of habitat for fish, birds and plants .
When severe storms landfall a higher sea level causes larger temporal and intensity that can destroy everything in their path.
In addition, hundreds of millions of people live in areas that are increasingly vulnerable to the risk of flooding. The current sea level rise would force them to abandon their homes and move to another area. The low-lying islands would be completely submerged.
How it will evolve in the future?
Most predictions claim that global warming will continue and probably accelerate. It is likely that sea levels continue to rise, but it is impossible to predict exactly how fast. A study conducted recently estimated that sea levels will rise by between 0.8 and 2 meters by 2010, enough to flood many of the cities on the east coast of the United States. The most alarming estimates, including stating that the ice sheet covering Greenland could melt completely, estimate the sea level rise 7 meters, enough to submerge London and Los Angeles.