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Sea Ice, Glaciers and Sea Level Rise

(modified from http://www.usc.edu/org/cosee-west/Mar2109/ Sea%20Ice%20Glaciers%20and%20sea%20level%20rise%20lesson.pdf)

Introduction

There is scientific consensus that global climate is changing, and that our poles (bothnorth and south) are warming. This warming is having an affect on all that snow and ice.

As the world warms, what will happen to sea level when floating sea ice melts?

When ice on land melts?

NASA: Global Temperature Anomalies

Materials (per group):2 clear cups4 ice cubes of similar sizeWater2 Popsicle sticksMarker

Procedures:

1. Place two ice cubes in one cup. Leave the other cup empty for the moment.2. Fill the cups with water until the water level is even in both. One cup will have ice

cubes in it, while the other will just have water.3. Mark the water level of both cups with the marker.4. Set both popsicle sticks over the cup without ice cubes. Place them far enough apart

so that they are not touching, but that you can still rest two ice cubes on top of them.5. Set two ice cubes on top of the popsicle sticks.6. Predict what will happen.

Hypothesis 1: What do you think will happen when the ice cubes floating in water melt?

Hypothesis 2: What do you think will happen when the ice cubes resting on the popsicle sticks melt?

7. Wait for both ice cubes to melt.8. Measure the water levels in each cup after the ice cubes have melted.

Questions

1. Describe what happened to the water level in each cup.

2. Were your original hypotheses correct?

3. Based on your experiment

a. Does melting sea ice cause sea level to rise?

Explain.

b. Do meting glaciers causes sea level to rise?

Digging Deeper: The West Antarctic Ice Sheet

There is good reason to keep a close eye on the West Antarctic Ice Sheet. If it were to melt, global sea level would rise nearly 20 feet!

Scientists all over the world are trying to understand the stability (or instability) of the WAIS in the face of current climate change. They do this by looking at today’s changes on the ice sheet. They also do this by looking at how the ice sheet has changed in the past.

The National Science Foundation, along with NASA and the National Snow and Ice Data Center (NSIDC), support the West Antarctic Ice Sheet Initiative. This is a “multi-disciplinary study of rapid climate change and future sea level.” Scientists are urgently collecting data to help predict what will happen to the WAIS and to our coastlines.

Why does the WAIS seem more worrisome than the rest of Antarctica’s ice? If you look at the map below, the East Antarctic Ice Sheet looks much bigger. In fact it contains about 10 times as much ice as the WAIS! If it were to melt, global sea level would rise 60 meters (nearly 200 feet).

Both the WAIS and EIAS rest on bedrock. One big difference between them – and the reason scientists are more concerned about the WAIS -- is that the WAIS rests on sloping bedrock that is below sea level, whereas the EAIS rests on bedrock well above sea level. The WAIS is in contact with warm, upwelling ocean water and is also flowing downslope and calving into the Southern Ocean.

Digging Northward: Arctic Ice

Melting of Arctic sea ice (see the bright colors in the map to the right) has accelerated in recent years. Summer ice coverage has been at or near record lows since 2001. The “most melted” summer was 2007, followed by 2011. You can see this in the graph below.

As you saw in the experiment, melting Arctic sea ice will not raise sea level by itself. However, melting Arctic sea ice does impact climate. That is because ice reflects much of sun’s energy back to space (albedo), whereas the ice-free ocean absorbs heat.

This will help further raise Arctic temperatures, which are already rising more steeply than the rest of the planet. Subsequent melting of Arctic land ice – glaciers, ice caps, and Greenland’s ice sheet – will indeed contribute to rising sea level, by up to 3 – 5 feet.