Lessons in Sea-Level Rise
What is sea-level rise and how does it affect us? This "Teachable Moment" looks at the science behind sea-level rise and offers lessons and tools for teaching students about this important climate topic.
The students will:
examine the satellite data graphs
connect their observations to literature about sea level rise
draw conclusions about the impact of sea level rise
discuss their findings with others
NASA Phenomenon Connection
NASA keeps track of sea level change and its causes from space. Since 1992 NASA, NOAA and European partners have been tracking global ocean surface topography with joint ocean altimeter satellite missions from an orbit 1,336 km above the ocean surface. The spacecrafts' radar altimeters measure the precise distance between the satellite and sea surface. This record began with TOPEX/Poseidon, followed by Jason-1 and the Ocean Surface Topography Mission on Jason-2, and will be continued by Jason-3.
Radar altimetry from orbit revolutionized global sea-level observations, capturing variations across most of the planet’s oceans every 10 days, as well as at other time intervals. The first measurements precise enough to track changes in global mean sea level began with the launch of the NASA-CNES TOPEX/Poseidon satellite in 1992 (CNES is the French space agency). The spacecraft was equipped with two altimeters and a microwave radiometer, which corrected for the effects of water vapor on radar signal transmission; other instruments ensured precision tracking of the satellite’s orbital position [Mitchum et al. 2010].
The advent of gravimetric measurements with the twin GRACE satellites in 2002, along with more recent deployment of floating Argo sensors, opened the way to “closure” of the sea level budget—that is, when the sum of observed ocean mass and density changes equals total sea level change [Leuliette and Willis, 2011].
GRACE measures changes in water mass, including terrestrial storage in the form of groundwater, rivers, snow and ice, and mass changes within the ocean itself, as well as the movement of water between land and ocean.
Early attempts did not achieve closure of the sea level budget for four-year trend lines [Willis et al., 2008, Chang et al., 2010], leading to concerns about possible instrument drift. More recent efforts, however, led to reports of closure for more extended periods, including a NOAA report covering 2005 to 2013 ("The Budget of Recent Global Sea Level Rise, 2005-2013," by Eric Leuliette).
The deployment of floating sensors across the world’s oceans, known as the Argo project, reached a critical mass in 2007, with some 3,000 of the devices set adrift to measure temperature and salinity in the ocean’s upper 2,000 meters[Leuliette and Willis, 2011]. These sensors profile ocean expansion, the thermosteric sea-level rise that, as we have seen, is a consequence of ocean heat absorption. The Argo floats play critical roles in recent studies of trends in ocean heat content, which generally show increased warming over decades. One recent estimate, covering 1955 through 2010 [Levitus et al., 2012], relied upon historical data and more modern readings from the World Ocean Database 2009, additional data from NOAA through 2010, and Argo data that became available in early 2011. Some of the Argo data had been corrected by Argo quality-control teams, although uncorrected data also were used. (The authors say that temperature measurements from the floats, unlike salinity measurements, show few instances of data drift.)
What sea level data is collected and why are these important?
When do we see the most change in sea level?
How might change in the Hydrosphere affect changes in the other parts of the Earth System?
The questions involved in this activity refer to interactive online graphs. For the most accurate results, be sure students have access to the Internet. However, if Internet access is not available for students, consider projecting one set of graphs for the whole class to consult and appointing one student to mouse over appropriate points. Alternately, print hard copies of the graphs for students to mark up and estimate using their graph-reading skills.
Because preconceived notions may influence the perception of fact, be sure to have students do the math first, then attempt to draw scientific conclusions. This sequencing will provide them with independent data from which to make statements.
See NASA's JPL for access to full lesson plan and resources.