Future of the Cryosphere

Part A: Sea Level Rise

A scientific report endorsed by the United Nations states that unless greenhouse gas emissions are curtailed, average global temperatures may rise between one and three degrees Celsius (two and six degrees Fahrenheit) in the next hundred years. The ramifications of a temperature change at just the low end of this range would be severe. A one-degree Celsius (two-degree-Fahrenheit) change in temperature is predicted to result in a one-meter (three-foot) rise in sea level, which would displace millions of people in coastal cities and low-lying islands. For example, virtually all of the agricultural land in Bangladesh would be covered in seawater and rendered unusable. Another consequence of increased global temperatures would be an acceleration of glacial melt in mountain valleys, which would in turn result in massive flooding in their drainage basins. Rivers that are currently glacier-fed would dry up, impacting agriculture and other economic activities. [Excerpted from Teachers' Domain Background Essay for Mountain of Ice: If the Ice Melts .]

1. Using the materials provided by your instructor, design a model or experiment to demonstrate how melting sea ice and land ice contribute to sea level rise.



Checking In

Using your model to help you, answer the following questions to check your understanding of how melting sea ice and land ice contribute to sea level rise.

• Did your model support your answer to Stop and Think question 1? Explain.
• How could you make your model more accurate?


2. Look at the plot below of sea level rise data from the last 120 years or so.




Sea level rise during the last century as recorded at 23 geologically stable tide gauge stations, and for the last 15 years through satellite observations. Image source: Wikimedia Commons.




Checking In

Using the graph above, answer the following questions to check your understanding of recent sea level rise.

• What is the average rate of sea level rise in cm/year for the period of time covered by the graph?
  Show me the answer
  Hide
  Approximately one sixth of a centimeter per year, or 0.17 cm/year (20 cm in 120 years).
• At this rate, how long would it take for sea level to rise 1 meter? 10 meters?
  Show me the answer
  Hide
  • 1 m: approx. 600 years
  • 10 m: 6,000 years



According to the U.S. Geological Survey , "Global sea level and the Earth's climate are closely linked. The Earth's climate has warmed about 1°C (1.8°F) during the last 100 years. As the climate has warmed following the end of a recent cold period known as the "Little Ice Age" in the 19th century, sea level has been rising about 1 to 2 millimeters per year due to the reduction in volume of ice caps, ice fields, and mountain glaciers in addition to the thermal expansion of ocean water. If present trends continue, including an increase in global temperatures caused by increased greenhouse-gas emissions, many of the world's mountain glaciers will disappear. For example, at the current rate of melting, most glaciers will be gone from Glacier National Park, Montana, by the middle of the next century. In Iceland, about 11 percent of the island is covered by glaciers (mostly ice caps). If warming continues, Iceland's glaciers will decrease by 40 percent by 2100 and virtually disappear by 2200. Most of the current global land ice mass is located in the Antarctic and Greenland ice sheets (table 1). Complete melting of these ice sheets could lead to a sea-level rise of about 80 meters, whereas melting of all other glaciers could lead to a sea-level rise of only one-half meter."



Estimated potential maximum sea-level rise from the melting of present-day glaciers (Data source: USGS )


Location	Volume (km3)	Potential sea-level rise (m)
East Antarctic ice sheet	26,039,200	64.80
West Antarctic ice sheet	3,262,000	8.06
Antarctic Peninsula	227,100	0.46
Greenland	2,620,000	6.55
All other ice caps, ice fields, and valley glaciers	180,000	0.45
Total	32,328,300	80.32





3. Launch the interactive Mountain of Ice: If the Ice Melts. NOTE: the interactive will open in a new window.
4. Click on the images to see how coastlines around the world would look if the Western or Eastern Antarctic Ice Sheet melted, or how they looked 20,000 years ago at the height of the Ice Age.
5. Look carefully at the image below, which highlights areas of the world with elevations near current sea level.
   

   Image by Robert A. Rohde/Global Warming Art. Click image for larger view.
   
   

   Stop and Think

   2: According to the map, what areas of the world will be most threatened if sea level rises by a few meters? Visit this web site to look at additional close-up regions of areas at risk. Would large-scale melting of ice sheets only impact countries at high latitudes? Explain.

   3: The plot above only shows coastal areas that are at or near current sea level. There are also island nations at risk of entirely disappearing as a result of sea level rise. Do an Internet search to find at least one example. Then answer the following questions:

   • What is the name of the island nation?
   • What is the nation's average elevation?
   • What is the nation's population?
   • How soon does this nation expect to be affected by sea level rise?
     
     

   4: Describe the consequences the United States may face if sea level rises by just a few meters. Give specific examples of coastlines, cities, industries, and habitats that would be impacted.




Discuss

As a class, discuss what you've learned about the cryosphere.

• What is the cryosphere?
• How and why does the cryosphere change over time and space?
• What are the timescales associated with changes in the cryosphere?
• How do climate and the cryosphere influence each other?