Unit 3: Warm with a Chance of Melting
How are recent air temperature trends influencing Greenland's ice mass? Are ice mass changes in Greenland spatially and temporally uniform? In this unit, students use atmospheric and geodetic data (GRACE, InSAR, altimetry) to investigate the location, magnitude, and causes of ice mass changes in Greenland.
Unit 3 Learning Outcomes
- Students will predict where the greatest Greenland ice mass change has occurred based on Greenland temperature, snowmelt, ice velocity, and ice elevation data from 2000 to 2005.
- Students will identify similarities and differences between their spatial predictions and GRACE (Gravity Recovery and Climate Experiment) observations and propose reasons for any differences observed.
- Students will examine time series to evaluate the relationship between air temperature changes and ice mass changes in Greenland.
Unit 3 Teaching Objectives
- Characterize Greenland's 21st century, non-uniform ice mass changes using snowmelt, ice velocity, ice elevation, and GRACE data.
- Develop ocean-atmosphere-cryosphere explanations for the spatial and temporal variations observed.
- Promote skills in reading and interpreting graphs and maps, some of which illustrate snapshots in time and some of which illustrate changes over time (time series).
- Facilitate a synthesis of multiple types of measurements (InSAR, IceSAT, and passive microwave data) to make predictions about the behavior of a natural system.
- Encourage reflection about the various local, regional, and ice sheet-wide mechanisms that may contribute to changes in a natural system and interplay and competition between these mechanisms.
- Encourage reflection about the role of uncertainty in scientists' understanding of a complex system.
Context for Use
The content in Unit 3 is appropriate for introductory geology, oceanography, meteorology, and other geoscience courses; sophomore-level courses in which geodesy and/or climate studies are being introduced; or non-geoscience courses where climate studies and/or the nature and methods of science are being investigated. Unit 3 activities can easily be adapted to serve small- or large-enrollment classes and can be executed in lecture and lab settings as a series of interactive lecture activities, a lengthier in-class activity, a collaborative lab exercise, or as part of a ~two-week investigation of the use of geodesy to understand cryosphere and sea level changes using the entire Ice Mass and Sea Level Change module. In the Ice Mass and Sea Level Change module, this unit follows Unit 2: Temperature--a global trendsetter on air temperature and sea level projections and precedes Unit 4: An uplifting story of sea level change on the contributions of short-term, post-glacial rebound and melting to sea level change. If the entire two-week module will not be utilized, we recommend pairing Unit 3 with Unit 4: An uplifting story of sea level change to give students an opportunity to consider the role of local uplift on sea level and gain experience reading and interpreting bedrock GPS time-series. Alternatively, Unit 3 could be paired with Unit 5: Regional sea level changes—a tale of two cities to consider potential societal impacts of sea level change.
Description and Teaching Materials
Prior to the class meeting, all students should complete brief preparation exercises on reading and interpreting air temperature data and how GRACE data are obtained and used. The temperature preparation exercise requires two color temperature maps which may be provided to students in hard copy or electronically. The GRACE preparation exercise requires students to watch a ~7-minute video (Grace: Tracking Water From Space) that is available online.
- Air Temp preparation exercise (student) (Microsoft Word 2007 (.docx) 1.3MB Sep24 15)
Group A: Air temperature and snow melt (student) PDF (Acrobat (PDF) 4.4MB Dec8 17)
- GRACE preparation exercise (student) (Microsoft Word 2007 (.docx) 619kB Jun23 19)
GRACE preparation exercise (student) PDF (Acrobat (PDF) 745kB Jun23 19)
The group work portion of Unit 3 is a jigsaw activity.
At the beginning of the class meeting, each student receives handout A, B, or C. In groups of three to four, students with the same handout work together and answer a variety of questions about their data set. For efficiency and consistency, four study sites have been chosen for Unit 2: Petermann Glacier, Jakobshavn Isbrae, Helheim Glacier, and an interior study site in northeast Greenland. These study sites are circled on every map given to students.
- Group A students look at Greenland air temperature maps from 2001 vs. 2010 and Greenland surface snowmelt maps showing average cumulative melt days from 1979–2007 vs. cumulative melt days from 2012.
- Student version: Group A: Air temperature and snow melt (student) (Microsoft Word 2007 (.docx) 4MB Dec8 17)
Group A: Air temperature and snow melt (student) PDF (Acrobat (PDF) 4.4MB Dec8 17)
- Instructor version:
- Group B students look at a Greenland ice velocity map from 2008/2009 and ice velocity maps of Helheim, Petermann, and Jakobshavn showing ice velocity for 2000/2001 and the 2008/2009 vs. 2000/2001 ice velocity differences.
- Group C students look at a Greenland ice elevation map illustrating surface elevation change from 2003–2007 and ice elevation time series through 2012 for Helheim, Petermann, and Jakobshavn, plus the interior study site.
Each handout includes two blank Greenland maps—one labeled "prediction" and one labeled "evidence" (see figure below). Still in their ABC groups, students use their respective data sets to predict ice mass change for each of the four study sites. On the "prediction" map, they shade areas where they expect a large decrease in ice mass (dark red); slight decrease in ice mass (light red); no change in ice mass (white); slight increase in ice mass (light blue); and large increase in ice mass (dark blue). To ensure that their predictions are not arbitrary, students are instructed to provide written notes for each study area justifying why they made a particular prediction for each study area. These written notes go on the "evidence" map. Students should be given examples of words/phrases as prompts for creating their evidence maps.
Students divide into new teams—team size depends on enrollment, but there should be at least one group A, B, and C representative. (Teams of three are ideal for discussion, but teams of up to six students will work.) Via a series of discussion questions in the handout, each student provides a brief explanation of his/her data set and presents his/her ice mass change prediction and evidence maps. Each team compiles the results of their predictions from snowmelt, air temperature, ice velocity, and ice elevation data in a table and creates a team prediction map. At this point, the instructor may choose to have a group report-out, with selected teams sharing their predictions and rationale.
- Student version: Unit 3: Combined group data activity (student) (Microsoft Word 2007 (.docx) 2.9MB Dec8 17)
Unit 3: Combined group data activity (student) PDF (Acrobat (PDF) 3.5MB Dec8 17)
- Instructor version:
Teams then receive GRACE-derived Greenland maps showing ice mass changes from 2003 to 2004, 2009, and 2012 and compare their predictions to GRACE observations. They identify spatial similarities and discrepancies between their predictions and the GRACE data, propose ideas for the ice mass changes observed, and make some ice mass change calculations using a GRACE time series.
Unit 3 concludes with a large group discussion about the following topics:
- Examples of the mechanisms potentially contributing to ice mass changes in Greenland. The Ice Mass and Sea Level Changes module focuses on three mechanisms—increases in air temperature, increased snow accumulation (this mechanism is applicable to the NE interior study site), and meltwater draining to the base of the glacier—although instructors are welcome to incorporate more mechanisms into the discussion as time and interest allows;
- Suggestions about why students' predictions about ice mass changes based on snowmelt, ice elevation, and ice velocity data may not correspond to ice mass changes revealed by the GRACE data.
Unit 3: Discussion slides (PowerPoint 2007 (.pptx) 8.3MB Dec8 17)
Unit 3: Figures (PowerPoint 2007 (.pptx) 15.6MB Dec8 17)
Teaching Notes and Tips
Depending on the elements of Unit 3 that are implemented in class, the duration of discussion and brainstorming about the mechanisms contributing to ice mass changes in Greenland, time spent on the GRACE data, and the teaching techniques employed (for example, some instructors might choose to implement the entire unit as a group work exercise, while others might rely more heavily on whole-group discussion/lecture), Unit 3 could occupy two to four hours of class time. The class meeting before implementation, each student should be given a copy of the preparation exercise. Prior to classroom implementation, copies of the group activity worksheet used in Part 2 should be copied for each student. Each student needs at least two colored pencils (preferably, every student will have the same colors for consistency on their maps). A copy of the compiled activity worksheet used in Part 3 should be available for each ABC group. Color copies of the following should be printed for Parts 2 and 3—quantity-wise, there should be a complete set of color copies for each ABC group that will convene in Part 3:
- Air temperature and snowmelt maps
- Ice velocity maps for Helheim, Jakobshavn, and Petermann
- Ice elevation map for Greenland
- Ice elevation time series for Helheim, Jakobshavn, Petermann, and NE Interior (these do not need to be in color)
- GRACE maps
PowerPoint presentations should be downloaded. We also recommend providing reference maps with the four study areas circled for each group.
Here are some notes about implementing Unit 3. For additional teaching tips and descriptions of classroom implementation strategies, refer to the Instructor Stories page.
- One challenge in working with the temperature, snowmelt, ice elevation, ice velocity, and GRACE data is that all of the data sets are from slightly different years. This will certainly influence students' predictions. We anticipate that students will indicate that more temporally consistent data sets would improve their ability to make predictions . . . but these are the data that exist!
- Unit 3 has specifically been scaffolded such that students make inferences about how their data can be used to think about ice mass changes without any explicit discussion or guidance about glacial dynamics. Before students learn about mechanisms (namely, meltwater drainage to the base of a glacier and snow accumulation) that can influence ice mass, we want them to think about how remotely sensed data are used to understand changes in ice mass, limitations of these data, and the role of uncertainty.
- In classroom testing, students working with the ice velocity data consistently required more time to complete their portion of the exercise than the snowmelt and ice elevation groups. There are several potential solutions to this issue, including making the ice velocity groups larger than the snowmelt and ice elevation groups so that students may divide the labor within the ice velocity data set; eliminating some of the ice velocity questions to streamline their work; or eliminating one of the study sites within the ice velocity data set. (We do not necessarily recommend doing the latter as the NE Interior study site has already been eliminated for the ice velocity data set.)
- It is imperative that students have an adequate number of color data sets. Specifically, each ABC (snowmelt/ice elevation/ice velocity) group of students should have its own complete color data set.
- Some users reported that students found making two prediction maps (the first using only one data set, the second synthesizing all of the data sets) too repetitive. As they are making their final prediction map, it is important to encourage students to look carefully at the snowmelt, ice elevation, and ice velocity data for each study area, determine whether the data sets all lead to the same prediction about ice mass change (they do not!), and make difficult decisions about which of the data sets should be most influential in their final predictions.
Formative assessment:Example #1: Faculty may collect student predictive and evidence maps at the end of the class meeting, either one set from each student or one combined set of maps from each group after snowmelt, ice elevation, and ice velocity representatives have pooled their data.
Example #2: Depending on the classroom setup and time constraints, faculty may choose to have group report-outs after the snowmelt, ice elevation, and ice velocity representatives have pooled their data. The faculty member could moderate the report-outs by projecting a slide of the prediction and evidence maps, asking selected groups for their predictions and rationale, populating the maps as the groups respond, and asking for alternative predictions and rationale from other groups. Alternatively, individual groups could be called to the front of the classroom to populate the maps (perhaps one group for each of the four study sites.)
Summative assessment questions:
Which of the following sets of measurements suggests that a particular glacier's ice mass is increasing?
A. decreased snowmelt, decreased ice velocity, increased ice elevation
B. increased snowmelt, increased ice velocity, increased ice elevation
C. increased snowmelt, increased ice velocity, decreased ice elevation
D. decreased snowmelt, decreased ice velocity, decreased ice elevation
Make a sketch of a marine terminating glacier whose overall mass is decreasing. On your sketch, label and explain at least two processes that could be contributing to the glacier's loss in mass. In addition, give two examples of measurements that scientists could use to understand how the glacier's mass is changing over time. How would these measurements change over time to suggest to scientists that the glacier's mass is decreasing?
(Alternatively, a simple schematic of a glacier could be provided so that all students are starting with the same template.)
Scoring: Concept sketches may be assessed using a rubric. Here is an example assuming that this is a 10-point question:
Example Unit 3 Concept Sketch Rubric (Microsoft Word 2007 (.docx) 85kB Oct1 15)
References and Resources
- Video: GRACE: Tracking Water From Space
- Video: NASA: Measuring Elevation Changes on the Greenland Ice Sheet
- Video: Beneath Greenland's glaciers, a huge, flowing plumbing system. Animation of meltwater's influence on ice sheet behavior from Woods Hole Oceanographic Institution.
- Air temperature: Comiso, Josefino C., and Dorothy K. Hall. "Climate trends in the Arctic as observed from space." Wiley Interdisciplinary Reviews: Climate Change 5.3 (2014): 389-409. (data from pers. comm.)
- Gravity data: GRACE (Gravity Recovery and Climate Experiment)
- Gravity data: GRACE data findings in Greenland
- Ice elevation: Csatho, B, et al. "Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics." Proceedings of the National Academy of Sciences. 2014. Note - PNAS allows reuse of images for educational purposes. Copyright is retained by National Academy of Sciences.
- Ice elevation: Pritchard, M., D. Hamish, et al. "Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets." Nature 461.7266 (2009): 971-975.
- Ice velocity: Rignot, E., and J. Mouginot. "Ice flow in greenland for the international polar year 2008–2009." Geophysical Research Letters 39.11 (2012).
- Snow melt data: Greenland snow melt from National Snow and Ice Data Center
- GRACE data: Bevis et al Accelerating changes in ice mass within Greenland, and the ice sheet's sensitivity to atmospheric forcing PNAS (2019).
Additional Resources for Instructors:
- The GETSI majors-level module Our Changing Climate has presentations with more technical information on altimetry, GRACE, and InSAR in Units 2 and 3.
- Overview of Satellite Radar Altimetry (PowerPoint 2007 (.pptx) 226.3MB Nov13 19)
- Overview of how GRACE satellites measure mass changes (PowerPoint 2007 (.pptx) 10MB Nov8 19)
- Overview of using InSAR to measure ice velocity (PowerPoint 2007 (.pptx) 105.2MB Nov13 19)
- Moulin Blanc: NASA Expedition Probes Deep Within a Greenland Glacier. Includes short video showing Greenland moulins and how they are studied.
- InSAR, a tool for measuring Earth's surface deformation. 2-page summary that provides an overview of how InSAR works and some of its Earth science applications.
- Why is it hard to predict the future of ice sheets? (Vaughan and Arthern, 2008). Focus on physical ice sheet dynamics and uncertainty in predicting ice sheet behavior.
- University of Maine Climate ReAnalyzer