Timothy J. Chiaverini
According to the IPCC, the average temperature of the global ocean has increased to depths of 3000 meters, and the ocean has been absorbing over 80 percent of the additional heat. The warming of the ocean causes seawater to expand, increasing the volume of the water and contributing rising sea levels.
5
In addition ice tends to reflect sunlight while sea water absorbs sunlight. There has been a measurable reduction in mountain glaciers and snow cover in both hemispheres. These widespread decreases in glaciers and ice caps have contributed to sea level rise due to the reduction in ice cover.
6
One common misconception is the perception of a direct cause and effect relationship between sea level rise and the melting of glaciers. Students may think that melting massive amounts of ice simply increases the amount of water in the ocean. Although land-based ice sheets would add volume to the earth's oceans if they melted completely, floating polar ice sheets would not add volume if they melted. Another significant threat to current sea levels lies in the principle of thermal expansion. Finally, the addition of massive amounts of fresh water to our salt water oceans is a concern, since the density of salt water is greater than the density of fresh water.
A current central issue in ocean climate theory is to understand the possible links between the variability of temperature and salinity anomalies and that of weather and climate fluctuations on the intraseasonal to decadal time scales.
7
The reasons for thermal expansion lie in the properties of almost all substances, in liquid, gas or solid states. When substances experience changes in temperature, their properties change in various ways. Electrical properties and sizes can change, and these changes can be used to measure the change in the temperature of the substance. Nearly all materials expand when their temperature is raised and shrink when their temperature is lowered.
8
When a substance is heated, the temperature change activates its particles causing them to move farther apart. Simply put, this change in particle behavior is obviously accompanied by an increase in volume. This is Thermal Expansion. Therefore, although the salinity of seawater changes with time due to the changes of freshwater flux into the ocean, its effect on sea level change may have been underestimated by the current model setup. Consequently, the sea level calculation is dominated by thermal expansion of the water column.
9