Controversies in the Earth Sciences

Reading Assignment: Alaskan Glaciers and Antarctic Ice Sheets

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How much water is in a cubic kilometer of water?

The volumes discussed in studies like these (for example, the amount of ice loss, the amount of meltwater produced, etc.) are given in cubic kilometers. Do you have any sense about how much water is in a cubic kilometer? Here's a little estimation that puts this into perspective

Video: Cubic Kilometer (3:44)

Cubic Kilometer
Click here for transcript of Cubic Kilometer.

PRESENTER: When I try to picture really big or really small numbers, I like to break it down into something else that I can understand a little better just so that I have some idea of what's going on. 

In this lesson, we read a paper by this group of scientists, and they estimated that between the 1950s in the 1990s, Alaskan glaciers lost an average volume of around 50 cubic kilometers of water every year. And then between the 1990s and the early 2000s, those same glaciers lost closer to 100 cubic kilometers per year of water. Do you have any idea how much water is in a cubic kilometer, much less several cubic kilometers? Let's do a little calculation to try to put that into perspective. 

What if I took one cubic kilometer of water and I wanted to apportion that water out for the entire world so that every single person in the world would get some of that cubic kilometer. How much water would everybody get? Well, we can do that calculation. 

If I have one cubic kilometer, that is a box with 1,000 meters on a side. So that equals 1,000 times 1,000 times 1,000 meters. That is 1 billion cubic meters. And I also know that in one cubic meter, there are 1,000 meters. 

So if we have 1 billion cubic meters, and there's 1,000 liters in each cubic meter, that means we have 10 to the 12th meters of water in a cubic kilometer. Now's a good time for me to give a shout out to my 12th grade government teacher from Blacksburg High School, Karen Colson, who explained to our class that she thought that one of the reasons Jimmy Carter did not get elected to a second term is because he tried to convert this country to the metric system. And we all know how well that worked-- not very well. So I don't think most people can actually even picture what a liter probably is. But all of us non-scientist, milk-drinking Americans probably know what a gallon looks like. It looks like this. And there's about four liters in every gallon. 

So if I have 10 to 12 liters and I divide that by 4 to get gallons, then that's about 0.25 times 10 to the 12th gallons. And as of late 2012, there were about 7 billion people in the world, so we just have to divide this number by 7 billion. And we'll figure out how many gallons of water everybody is going to get. 

And that number is this. We can write this in a much more normal way by just moving this decimal three places over to take care of this exponent. And what we find out is in each person in the world gets about 36 gallons if we had one cubic kilometer of water and we apportion that up over everybody. 

But remember, in this paper we're not talking about one cubic kilometer of water. We're talking about between 50 and 100 cubic kilometers of water every year. That is a lot of water, my friends.

Credit: Dutton


The contribution of land glacier melting to global sea level rise has been explored in a recent study of Alaskan glaciers. In this study, airborne laser altimetry was used to determine the mass and thickness of over fifty glaciers. This method is a huge improvement over previous studies that have used complicated and imprecise mass-balance calculations to estimate the rate of glacial melting. The results of this new study show that Alaskan glaciers contribute more meltwater than was previously thought and are losing mass faster than was previously thought. When you read these papers, think about how the results of this study will be incorporated into global climate models.

Then, read a paper that is about climate modeling in which researchers construct a model that does a better job of fitting the sea level and temperatures of the past than has previously been accomplished. The key was adding in warming ocean currents, a warm atmosphere, and a chain reaction of collapsing ice shelves.

As usual, for the Alaskan glaciers paper, I recommend reading the accompanying Perspective (Meier and Dyurgerov, 2002) first, then reading the scientific paper (Arendt et al., 2002). For the modeling work, I recommend reading the accompanying News Focus first (Tollefson, 2016) and then the scientific paper (DeConto and Pollard, 2016).


  • Meier, M. F., & Dyurgerov, M. B. (2002). How Alaska affects the world. Science, 297(5580), 350.
  • Arendt, A. A., Echelmeyer, K. A., Harrison, W. D., Lingle, C. S., & Valentine, V. B. (2002). Rapid wastage of Alaska glaciers and their contribution to rising sea level. Science, 297(5580), 382


  • Tollefson, J. (2016). Trigger seen for Antarctic collapse. Nature, 531, 562.
  • DeConto, R.M. and D. Pollard (2016). Contribution of Antarctica to past and future sea-level rise. Nature, 531, 591.

Questions for discussion:

  • What are the specific causes of sea level rise and how are these causes measured?
  • What factors contribute to predictions of future sea level rise? How does the new data detailed in Arendt et al.'s study impact sea level rise calculations? How does the new model in DeConto and Pollard's study impact sea level rise predictions?
  • What are the difficulties involved in making measurements of ice volume? What are the different methods used and how do they work?
  • How is past sea level reconstructed?

Participating in the discussion

The discussion component of this activity will take place over Week 1 of this lesson and will require you to participate multiple times over that period.

  1. Enter the "Alaskan Glaciers and Antarctic Icepapers" discussion forum.
  2. You will see the questions above already there
  3. Respond to a question that hasn't already been chosen by another student. If all questions have already been addressed, then select a question where you can further the discussion and post there.
  4. Return to the discussion periodically to read your classmates' postings and to respond by asking for clarification, asking a follow-up question, expanding on what has already been said, etc.

Grading criteria

You will be graded on the quality of your participation. Please see the rubric for teaching/learning discussions.