Thermal Expansion and Sea Level Rise
|Students investigate how thermal expansion of water might affect sea level.
|Adapted from Global Climates - Past, Present, and Future. EPA Report No. EPA/600/R-93/126 and recommended by Sandra Henderson
|one class period
Student Learning Outcomes:
- Completely fill the flask with very cold water (to improve visibility, dye can be added).
- Place the thermometer and glass tube into the cork as shown in the picture at the right.
- Place the cork (with tube and thermometer) into the mouth of the flask. The water should rise a short way up the glass tube.
- Have a student report the temperature of the water and mark the water level in the glass tube with marker.
- Ask students to predict what will happen to the water level when exposed to heat. Form a hypothesis or multiple hypotheses.
- Place the flask under the lamp. (Lamp should be aimed towards the water, not the top.)
- Turn on the lamp and within 5-10 minutes the water level in the glass tube will have risen.
- Discuss results, hypotheses, and how this example relates to the effect of global warming on sea level (pointing out the dissimilarity between the flask and ocean basins).
If global temperature increases, many scientists have indicated that an increase in sea level is one of the most likely secondary effects. Two factors will contribute to this accelerated rise in sea level. First, although the oceans have an enormous heat storage capacity, if global atmospheric temperatures rise, the oceans will absorb heat and expand. This is called thermal expansion. A greater volume of ocean water due to thermal expansion will lead to a rise in sea level. Second, rising temperatures will cause the ice and snowfields to melt, thereby increasing the amount of water in the oceans. It should be noted that only the melting of land-based ice and snow will increase sea level. The melting of floating ice will not affect sea level. This can be demonstrated to your students by partially filling a glass container with ice and water and marking the water level on the glass. When the ice cubes melt, note that the water level has not changed.
Throughout Earth history there have been periods of glaciation followed by warming trends in which the glaciers retreated towards higher latitudes and higher altitudes. At present, glaciers throughout the world are retreating and the amount of snow and ice at the poles is shrinking. The present interglacial warm period began about 14,000 years ago. At that time sea levels were about 75 to 100 meters lower than they are today. The sea level rose rapidly (up to 1 meter per century) as massive amounts of snow and ice melted. Today the rate of sea level rise is much lower at 15-17 centimeters per century.
However, the rate of sea level rise is increasing as the rate of global warming increases. An accelerated rate of sea level rise would inundate coastal wetlands and lowlands, increase the rate of shoreline erosion, cause more coastal flooding, raise water tables, threaten coastal structures, and increase the salinity of rivers, bays and aquifers.
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