Melting Ice and Rising Seas

1. Place one of your solid objects in each container, as close to the side as you can get it, leaving no gaps. This represents "land"; the rest of the container represents the "sea."
2. Place half of the ice cubes on top of the “land” in one container and the other half in the “sea” in the other container.
3. Add the same volume of water to both containers, making sure the water level stays below the edge of the “land” (click on photo below to enlarge).
   
   

Mark the water level of each container with a permanent marker. Next, place the ruler along on the side of each container to measure the water depth in millimeters. Record these water levels as your first observation of sea level. 

As the ice on “land” and in the “sea” melt, what do you predict will happen? Where do you expect the melted ice water to go? 

Measure the water level again at regular intervals, such as at the same time every hour, until all the ice has melted. (Tip: Set a timer to go off every hour.) This could take several hours. At each interval, record the time and the water levels you observe. Optionally, you can continue to mark the levels on the side of the container to help you keep track. 

After the ice in both containers has melted, graph the water levels you recorded at each time interval for both containers. Plot the data points on a graph, with time on the x-axis and water level on the y-axis. Connect the “land ice” points. What do you notice? Connect the “sea ice” points. What do you notice? How did the sea levels change, or not change, in each container?

What might change if you conducted your experiment under different conditions (for example, both containers in a warmer or cooler location)?

Rising sea levels mean the volume of water in the sea has changed. 

The land ice melted and flowed down into the sea, adding more water to the sea and causing the volume of the sea to change. The melted land ice is a new addition to the ocean and causes a change in sea level over time (as your graph shows!).

Sea levels are rising due to melting ice from glaciers and ice sheets found on every continent except Australia. As water from melted land ice pours into the ocean, the volume of water in the global oceans increases. 

What about the melting sea ice? Ice is less dense than water, which is why it floats. When ice melts, the resulting water is denser, so a particular mass of what had been solid ice will have a smaller volume when it becomes liquid water. This change in volume exactly offsets the small percentage of ice that is above the water's surface. Therefore, melting sea ice does not affect sea levels.

Melting ice isn’t the only culprit for sea level rise. Other factors in the environment also cause sea level rise, including the effects of heating liquid water. When liquid water is warmed up, it increases in volume (takes up more space), while the actual amount of water (number of water molecules) stays the same. This is called thermal expansion, and it’s causing sea levels to rise as sea water is warmed by higher air temperature and expands, taking up more space. Investigate the effects of thermal expansion yourself by trying the Swelling Seas Science Snack.

Teachers can introduce this activity by asking students what they know about ice:  Have you noticed what happens to the water level in a glass of ice water as the ice melts? Where do they predict water will flow once the ice melts in this experiment? At the end of the activity, ask students how they interpret the results (graph) in terms of the actual phenomenon of sea level rise. Which contributes to rising sea levels: sea ice or land ice?

Encourage students to think about the real land/sea environment. Where would water flow as land ice melts? Would land ice or sea ice melt faster? Is global ice melting due to warming of air, land, seawater, or all of the above? Variables to consider include effects of heating of continental materials (soil and solid rock) versus water and air, flow of melting land ice vertically below ground versus horizontally into oceans, and whether land ice or sea ice is more abundant globally.

Students can think like scientists by discussing how well this model represents the sea and land in real life. What might be missing and what could be simplified to improve our understanding of what the model represents? One example of improving this experimental model would be for participants to have control of the temperature around the model. Increasing the temperature around the model throughout the course of the experiment could help represent climate change, and would produce a different rate of sea level rise.

This Snack is also a great opportunity to have students think about data collection and interpretation. How would they report their findings to others who did not conduct the experiment? How could this be explained to make it clear to others? What do the results mean for understanding causes of sea level rise? What does a graph of a horizontal line mean as an observation? How would changing a variable in the model affect the trend in the data (examples: slope of line changes, all values decrease/increase equally)?

For younger students, this could be set up as a demonstration or station, which a class can observe over the course of a school day, marking the sides of the containers with the water levels every hour.

This Snack is adapted from an activity developed by the NASA Jet Propulsion Laboratory.