As global warming accelerates we are seeing another consequence of the resultant increased atmospheric temperature, sea levels are rising. Over the last century the Global Mean Sea Level (GMSL) has risen by 10-20cm, however over the last 20 years the annual rate of rise has been 3.2mm a year, roughly twice the average speed of the previous 80 years.
These sea level rises are as a result of the following three factors:
- Thermal expansion – the sea absorbs around 80% of the additional heat in the atmosphere and as the sea temperature rises it expands. About 50% of the sea level rise is simply due to the water occupying more space.
- Melting Glaciers and Polar Ice Caps – generally, large ice formations such as glaciers and polar ice caps shrink and expand at a balanced rate to give around the same amount of ice each year. However higher temperatures have led to greater summer melting as well as reduced snowfall due to later Winters and earlier Springs. The imbalance means there is more melted water runoff compared to ocean evaporation, resulting in sea level rise.
- Ice loss from Greenland and West Antarctica – increased atmospheric temperatures are causing the huge ice sheets of Greenland and West Antarctica to melt at an accelerated rate. In addition the higher sea temperatures are causing the massive ice shelves to melt from below, weaken and break off.
Even the small increases we have seen over the last century can have a devastating effect on the coastal environment. As the seawater encroaches further inland, it can cause a whole range of problems such as erosion, wetland flooding, aquifer and soil contamination, and lost habitat for plants, fish and birds.
The option of restoring the balance is not possible right now so we can expect sea levels rises for centuries and at rates greater than we are currently experiencing. The exact rates of rise are very difficult to predict and so estimates of sea level by 2100 range from an increase of 98cm to 7m, the latter being the result of a complete meltdown of the Greenland ice sheet. Even at the lower levels, this means many of the cities along the US East coast will be swamped, at the higher level even London will be under water.
The consequences of global warming means bigger and more powerful storms and as sea levels rise this means bigger and more powerful storm surges. Hundreds of millions of people are at risk worldwide, and everyone who lives near a coast line will be affected, with consequent huge loss of homes and even some whole islands.
This is a crisis in motion and we are making token gestures to combat the sea level rise, we need to take this seriously if we are to avert disaster. Or is it already too late?