GETSI Teaching Materials >Understanding Our Changing Climate > Unit 3: Global Sea-Level Response to Ice Mass Loss: GRACE and InSAR data
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This module is part of a growing collection of classroom-tested materials developed by GETSI. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
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Unit 3: Global Sea-Level Response to Ice Mass Loss: GRACE and InSAR data

Susan Kaspari (Central Washington University)
Bruce Douglas (Indiana University)

Summary

What is the contribution of melting ice sheets compared to other sources of sea-level rise? How much is the sea level projected to increase during the twenty-first century? In this unit students will use Gravity Recovery and Climate Experiment (GRACE) ice-mass loss time series from Greenland and Antarctica to calculate sea-level rise due to the addition of freshwater inputs from melting ice sheets, and use Interferometric Synthetic Aperture Radar (InSAR) ice-velocity data to extrapolate which regions of the ice sheets are losing the greatest mass. Sea-level rise from melting ice sheets is then contrasted to the other dominant causes of sea-level rise, including thermal expansion, melting glaciers, and changes in land water storage. Lastly, students will extrapolate how much sea-level rise will occur by year 2100 based on recent observed rates of sea-level rise and compare these values to sea-level rise projections from the Intergovernmental Panel on Climate Change.

Learning Goals

Unit 3 Learning Outcomes

Students will be able to:

  • Create time-series graphs of GRACE ice-sheet mass loss and calculate how much the ice loss contributes to sea-level rise.
  • Infer which regions of the ice sheets are losing the greatest mass by examining maps of ice velocity constructed from InSAR data.
  • Evaluate the sources of sea-level rise and rank the sources from largest to smallest contributors to sea-level rise.
  • Extrapolate how much sea-level rise is projected by 2100 based on current sea-level rise rates.

Unit 3 Teaching Objectives

  • Cognitive: Enable students to evaluate the contribution of melting ice sheets to sea-level rise.
  • Behavioral: Promote skills in making and interpreting graphs and using linear equations to estimate future sea-level rise.
  • Affective: Facilitate the students' appreciation that numerous processes must be considered when assessing the causes of sea-level rise.

Context for Use

The content in Unit 3 is appropriate for advanced Climate, Cryosphere, Geology, Geoscience, or Environmental-related courses conducted at the junior and/or senior level in which geodesy data can be introduced. Students should be cognizant that the Earth's climate is warming and have familiarity with the causes of the warming. The student exercise in Unit 3 requires access to computers to create Excel (or similar) graphs and calculations, so the exercise is best executed in a computer lab setting or could be assigned as an out-of-class activity. Students will need basic proficiency in creating graphs from time-series data set, including conducting linear trend analysis. Unit 3 is designed to follow Unit 2: Global Sea-Level Response to Temperature Changes. Some preparatory lecture time may be required to review how GRACE and InSAR data are acquired, and to review ice sheet anatomy and factors that influence ice sheet melt rates. If the entire two-week module will not be utilized, we recommend pairing Unit 3 with Unit 2: Global Sea-Level Response to Temperature Changes to give students an opportunity to investigate the dominant causes of current sea level.

Description and Teaching Materials

Introduction

In this unit students work through an exercise with GRACE and InSAR-derived ice velocity to better understand how the ice sheets are responding to the changing climate. The student exercise takes 1–2 hours that could be done in a lab period, stretched across several shorter class periods, or done partly/largely as a homework assignment. It works well to have students start the exercise in a one-hour class and then finish the remainder at home.

Background information for Unit 3 includes three PowerPoint presentations, several videos, and some readings. Instructors can decide what if any elements they want to assign as homework prior to class (such as reading or watching a video). The presentations include an overview of ice sheets and information on how GRACE and InSAR data are collected. The presentations are each fairly short and could be done in sequence.

Student Exercise Elements

The Unit 3 student exercise requires that students have access to a computer and Excel (or similar). Students can complete the exercise either during class or lab time, or as a take-home activity. However, Part 2 of the student exercise requires the student to acquire a data graph from the instructor, so if the assignment is given as a take-home activity the instructor will need to make sure they know how to access it.

In Part 1 of the student exercise, students use GRACE data to calculate mass change in the Antarctic and Greenland ice sheets, and examine ice-sheet velocity patterns using InSAR data. In Part 2 students calculate how much sea-level rise has occurred due to ice-sheet mass loss, and evaluate how the ice mass contribution compares to observed sea level. In Part 3 students evaluate sources of sea-level rise and rank the sources from largest to smallest. Lastly, in Part 4 students project how much sea-level rise will occur by year 2100 based on recent observed sea-level rise rates and compare this to sea-level rise projections from the Intergovernmental Panel on Climate Change. In Part 2 there are two graphs that are best given to students after they finish Questions 1–8. These are provided as separate handouts.

Teaching Materials

Teaching Notes and Tips

  • The unit requires use of computers. Ideally each student will have their own computer or laptop. At least there should be one computer per work group. If it is not feasible to use computers during the class/lab period, the instructor should take extra steps to make sure that students understand what is required of them to do the exercise outside of class.
  • The provided data files are in Excel. Students may actually prefer to use another spreadsheet program such as Google Sheets if they are working on their own computers. Google Sheets, while less powerful than Excel, has the capabilities to do the analyses for this unit. The Excel files should open fine in Sheets, but you may want to double-check this process yourself if you are not familiar with it. If you have students working on their own computers and thus have different software and different versions, it is better to emphasize the processes and how to query Help rather than try to show exactly the on-screen steps for the different programs.
  • The assignment is currently set up so that students work through the first 8 questions, and upon completion are given graphs with additional data to interpret for Questions 9 and 10. The assignment was set up this way so that the students weren't given graphical representation of all of the data initially. If the instructor chooses to have students complete this assignment outside of class, the students will need to be provided with the data for questions 9 and 10 ahead of time.
  • At the completion of this project, the instructor should consider having a class discussion of how much sea-level rise is expected by 2100, and the causes of uncertainty, which complements questions 15 and 16. While the upper projection of sea-level rise by 2100 is 1 m in the 2014 IPCC report, more recent studies indicate that sea level rise could be in excess of 1 m. Bamber et al, 2019, Ice sheet contributions to future sea-level rise from structured expert judgment addresses the potential range and sources of uncertainty.
  • If students will be completing the Stakeholder Report in Unit 5, it is useful for the instructor to remind the students that they may be incrementally working on Unit 5 by beginning to incorporate their findings from Units 1, 2, and 3.
  • One approach that can work is to spend one hour of class time on the exercise, making sure, during that time, of the students' understanding of each of the different calculations that need to be made. Then they can finish it at home using the same methods without the same oversight.
  • The Teaching with Spreadsheets across the Curriculum site provides support for teaching with programs such as Excel. If your students need supporting math practice, The Math You Need site provides an opportunity to brush up on skills such as graphing and unit conversion.

Assessment

Formative assessment of student learning may be done through conversations with individuals and groups during the exercise if it is done during class time. The student exercise is the summative assessment for the unit. The Unit 3: Student exercise assessment rubric (Microsoft Word 2007 (.docx) 23kB Nov8 19) PDF (Acrobat (PDF) 73kB Nov13 19) provides an example of how the exercise may be evaluated. We suggest including the rubric with the student exercise so the students know the criteria ahead of time. The discussion provides a less formal form of summative assessment and is also helpful for encouraging student reflection.

References and Resources

GRACE data

InSAR Ice Velocity

Ice sheets/Ice streams

  • The National Snow & Ice Data Center provides an overview of ice sheets, including descriptions of Greenland and Antarctica ice sheet structure and flow; climate; and how ice sheet mass balance is measured: https://nsidc.org/cryosphere/sotc/ice_sheets.html

Sea level

Climate Change


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This module is part of a growing collection of classroom-tested materials developed by GETSI. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »