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Where do icebergs like the one shown here come from? Where do they go? Experiments you can do in your kitchen will help you answer these questions (and others).

MATERIALS

For these experiments, you will need:

• two large ice cubes (micro “icebergs”) you can make by freezing water in two 2- or 3-ounce paper cups (Alternatively, you can use several regular-size ice cubes from an ice-cube tray.)
• a clear, colorless cylindrical plastic container, such as a 1-liter soft drink bottle with its top cut off (scissors do a good job) Alternatively, if you have one, any tall, cylindrical clear glass or plastic container will be fine.
• a plastic or glass cup or small bowl
• a clear glass bottle with a neck and screw cap, such as the bottles that are used to hold and dispense sauces (See the fourth experiment below for alternatives.)
• a container, such as a mug or canister, which can hold hot water and is deep enough for the glass bottle to fit into with much of the bottle submerged in the water
• a felt tip marker
• tap water from your sink
  
  See photo at right for examples of these supplies.

EXPERIMENT 1

Preparing the first experiment: Fill your cylindrical container about two-thirds full of cool tap water. On the side of the container, mark the level of the liquid in the container. Add one of your micro "icebergs" to the container and put the other one in the empty cup or bowl. (Alternately, add a few freezer-tray ice cubes to the water in the cylinder and the same number to the cup.) Mark the level of the liquid in the cylindrical container. Set it aside while you think about the questions in the following two paragraphs.

What did you observe when the ice was added to the water in the cylinder? Did you expect this result? Why or why not? What is the reasoning for your response?

Icebergs are formed from glaciers that are moving off the coast of the land that supports them, such as Greenland. When the tip of the glacier moves far enough off the land, it is no longer supported by the land and can break off. This is called “calving”; like a cow giving birth to her calf, the glacier gives birth to an iceberg as shown in the series of images below. Your addition of a micro “iceberg” to the water in your container was analogous to a calving glacier. The formation of an iceberg is represented by what happened when you added your micro “iceberg” to the water in the container. Based on the evidence from your experiment, what do you conclude about an iceberg and the sea it enters?

Images of a calving iceberg by Marianocecowski via Wikipedia

EXPERIMENT 2

Preparing the second experiment: Past experience probably tells you that solid ice floating in water does not hang around forever but ultimately completely melts. Let your container of water and micro “iceberg” sit until the ice has melted. Note the liquid level in the container.

EXPERIMENT 3

Preparing the third experiment: When the second micro “iceberg” in your cup has melted completely, add the liquid to the liquid in the cylindrical container. Mark the level of the liquid in the container.

A water cycle takes water vapor evaporated from the sea to the polar regions where it condenses as snow and falls on the land from which it can melt or form icebergs to replace the evaporated sea water. If the Earth were not warming, this cycle would maintain a constant average sea level and amount of land ice. But the cycle is unbalanced by the warming and land ice is being lost faster than it can be replaced. This “extra” water from icebergs and melting land ice (glaciers and ice sheets) adds more water to the oceans than they are losing by evaporation and the average level of the sea is rising, as in your experiments.

Also on our warming planet, every part warms, including the ocean, so we need to account for the effect of ocean warming as well.

EXPERIMENT 4

Preparing the fourth experiment: Add enough cool tap water to your bottle to fill it until the water is about halfway up the neck. Cap the bottle and put it in your refrigerator for several hours (or overnight). Remove the bottle from the refrigerator, swirl to capture any droplets that have condensed above the liquid in the neck, and mark the level of the liquid in the neck.

In a pan or kettle on the stove, prepare enough very hot, but not boiling, water to fill the mug or whatever container you will use to submerge the bottle. If you have a cooking thermometer, measure to check that the water is about 80-90 °C (175-195 °F). Put the mug in the sink or a pan to catch any water overflow. Place the bottle in the mug and carefully (hot water HAZARD) pour hot water into the mug to cover as much of the bottle as possible but not covering its neck. Allow the bottle to sit in the hot water for 15-20 minutes and then remove it from the hot water and mark the level of liquid in its neck. Discard the hot water in the mug. Set the bottle and its contents aside and observe how they react as they cool to room temperature.

Alternatives: If a glass bottle for this experiment is hard to find, you can use a plastic bottle. However, most plastic bottles will soften and change shape at high temperature, so you need to modify the heating procedure. Instead of very hot water, use hot tap water, which will probably be no more than 50 °C (125 °F). The effect you observe will not be as large as with the higher temperature but will be enough to draw conclusions about the temperature effect.

As water warms, it increases in volume (thermal expansion) and adds another factor to the rise of sea level, as shown in the figure below. As the warming sea expands in volume, its surface has to rise, since the liquid is constrained to stay inside its “container”, as in your experiment. Thus, rising sea level is caused by water added from melting land ice and volume increase from thermal expansion. Global warming is responsible for both these effects.

Modern remote sensing techniques make it possible to measure the overall rise in sea surface level as well as the individual contributions of ice melt and thermal expansion shown in the figure. Since 1993, satellites have been measuring the sea level (averaged over the globe). Its rise is evident from the graphical representation. The effect of added water from ice melt is found by determining the change in mass of the ocean. This is done with data from a pair of satellites that measure the change in gravitational attraction caused by the increasing mass of the ocean. The effect of thermal expansion is determined from the change in temperature of the ocean and the known increase in volume per degree temperature rise. The temperature is measured by an array of several thousand floats (called “Argo”) distributed throughout the ocean and periodically reporting their data via radio signals. These results are a few among many that are evidence that the Earth is warming and causing many changes that affect all life on the planet.