Valla Beach and global warming
Back home we were surprised at how much beach had disappeared while were away. Of course nature is intrinsically dynamic and beaches show this well. The sea level has been increasing worldwide since the last retreat of the glaciers about 10,000 years ago. I sometimes think of all the amazing Aboriginal art that is now lying out to sea.
The Global Mean Sea Level (GMSL) has risen by 4 to 8 inches (10 to 20 centimetres) in the last century and it is estimated that sea levels may be as much four feet higher by the year 2100.
Already, two of the islands that make up Kiribati have gone under the waves, and in early 2005 others were inundated by a high spring tide that washed away farmland, contaminated wells with salt water, and flooded homes and a hospital.
The immediate causes are:
- Thermal expansion: When water heats up, it expands. About half of the past century’s rise in sea level is attributable to warmer oceans simply occupying more space.
- Melting of glaciers and polar ice caps: Winter snow made primarily from evaporated seawater, used to balance summer melting. Higher temperatures caused by global warming have led to greater-than-average summer melting as well as diminished snowfall due to later winters and earlier springs. This imbalance results in a significant net gain in runoff versus evaporation for the ocean, causing sea levels to rise.
- Ice loss from Greenland and West Antarctica: As with glaciers and the ice caps, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt at an accelerated pace. Scientists also believe meltwater from above and seawater from below is seeping beneath Greenland’s and West Antarctica’s ice sheets, effectively lubricating ice streams and causing them to move more quickly into the sea. Moreover, higher sea temperatures are causing the massive ice shelves that extend out from Antarctica to melt from below, weaken, and break off.