Sea Level Rise

This is Part 1 of Lesson 3 of Project Resilience curriculum.

Students investigate how the combined effects of sea level rise and sinking land are projected to impact the Louisiana coast this century.

Learning Objectives

• Students will discover how global sea level rise is affecting locations in Terrebonne Parish, LA, depending on elevation.

Materials

• Project Resilience Slide Deck (slides 36-39)
• Projector & Computer
• Computers with Internet access & video streaming capability
• Sea Level Rise Student Sheet (PDF)
• NOAA Digital Coast Sea Level Rise Viewer

Preparation

• Preview the video and the NOAA Digital Coast Sea Level Rise Viewer.
• Print copies of the Sea Level Rise Student Sheet for each pair of students.

Directions

Navigate from the previous activity:

• Remind students what they learned about subsidence and sediment deposition in the previous lesson. Explain that while the land in the Bayou is sinking lower, there is another cause of land loss: the level of the ocean is rising higher. This combination leads to even more land loss in our region.

Explain how climate warming causes sea level rise. (20 min)

1. Watch from minute 7:43 to 18:36 of the Sea Level Rise video from the NOAA National Ocean Service (slide 37). There are pauses for discussion embedded within the video. If you would like students to discuss, pause the video whenever you see “Pause for Discussion” on the screen. Or, you may wish to provide students with the following guiding questions to consider as they watch the video.
   • How much of the sea level has risen in the past century? (Over the past century, there has been an average rise of 1.5 mm/yr, but the rate of the rising is increasing. It was 1.1 mm/yr early in the century and 2.79 mm/yr rise recently.)
   • How do we know? (measurements from tide gauges and satellites)
   • What are the two reasons for the increase in global sea level? (melting of glaciers and other ice on land, and thermal expansion of seawater)
   • How do increases in air temperature (global warming) cause sea level to rise? (the ocean is absorbing most of the extra heat, expanding water, and is causing ice on land to melt and add water to the ocean)
   • Why is the air temperature warming? (because there is extra CO2 in the atmosphere from fossil fuel emissions)
2. Ask students what the two reasons for sea level rise are that they learned about in the video: (1) seawater expands with heat, and (2) water is added to the ocean as land-ice melts.
3. Ask students why these two processes are happening now. (Because of climate warming.)
4. Show students that thermal expansion impacts the total volume of water in the ocean and also has a regional impact. Show students the NASA images of sea level (slide 38) as measured by satellites and point out the location of the Gulf of Mexico.
   • Areas where water is warm, experience higher sea level than areas with cold water. The water is warmed in the Gulf, causing a slightly higher sea level than areas with cooler water.

Investigate maps that show the impacts of sea level rise. (20 min)

1. Tell students that over this century, sea level will rise an average of 1.7-4.0 feet (0.5-1.2 m) worldwide. There are also a variety of unknowns, such as whether large parts of ice sheets will slip into the ocean and how ocean currents will change due to warmer temperatures. In the Gulf, that number will be higher due to the combined effect of less sediment coming in, subsidence, and sea level rise caused by climate warming.
2. In this activity, students will explore what the impact of higher seas and lower land will be in Terrebonne Parish.
3. Break students into pairs and pass out copies of the Sea Level Rise Viewer Student Sheet to each pair of students.
4. Assign each pair of students to a computer and have them open the Sea Level Rise Viewer. Tell students that the Sea Level Rise Viewer is a model. Models are used in Earth and environmental science to simulate real conditions so that we can predict how environments will be affected when there is a change
5. Guide students as they use the Sea Level Rise Viewer Student Sheet to answer questions and explore using the Sea Level Rise Viewer.
   • Students will first become familiar with the NOAA Digital Coast Sea Level Rise Viewer.
     • On the left side is a water level indicator. The blue circle indicates the water level compared to today. (MHHW means “Mean Higher High Water,” which is the average height of the highest tide recorded each day during the recording period).
     • Listed to the left of the water level indicator are the special map features.
     • At the top is a field where you can enter an address or town/city. Only coastal locations within the continental United States are included.
     • In the top right are options for the map and a key to the colors. Zoom in and out with the buttons in the lower right.
   • Students will enter “Terrebonne Parish, LA” into the search and then zoom into the map a bit.
   • Students should change the units on the water level indicator to metric (the switch is at the bottom of the indicator).
   • Give students the information that the water level in coastal Louisiana is rising at an average rate of 12.8 mm/yr.
   • Students will calculate how much sea level rise they’d expect by 2060 and 2100. Remind students that they will need to convert the units to meters by dividing by 1000.
     • For 2060, students should find a little over half a meter of sea level rise (if they do the assignment in 2019).
     • For 2100, students should discover about one meter of sea level rise.
     • Use a meter stick to help students visualize the water depths predicted for 2060 and 2100.
   • Students will move the water level indicator in the Sea Level Rise Viewer to visualize what areas of Terrebonne Parish are most vulnerable to sea level rise. Encourage students to use the zoom tool to find places familiar to them and see if they are vulnerable to sea level rise.

Discussion: Sensemaking (10 min)

1. Ask students to share what they discovered about the most vulnerable places and those that are safer from flooding. Share some examples and how much the water is expected to rise in those areas. Again, use a meter stick to help students visualize the water depths predicted by the Sea Level Rise Viewer.
2. Discuss the Sea Level Rise Viewer as a model. How does it accurately simulate real conditions? How is it simplified? Students may mention the following:
   • The model includes information about the elevation of the land surface, which is what allows it to identify what areas might flood in the future.
   • The model does not include predictions of areas where sediments may accumulate in the future, or how floodgates and human-built levees could change the outcome.
3. Ask students to share their ideas about why the amount of sea level rise is still uncertain.
   • Share that this is because there are some unknowns. For example, we don’t know when and how the Antarctic and Greenland ice sheets will break apart and end up in the ocean. Because the climate is warming, ice is melting. That’s certain. But, how quickly the ice sheets, which flow like molasses, move towards the ocean is difficult to predict and is one reason why there is a large range in sea level estimates.
4. Show students the A Changing Landscape image (slide 39), which shows projected land loss in Louisiana over the next 50 years if no action is taken. Explain that Louisiana has created a Master Plan to address land loss and other environmental challenges.
   • Alternatively, project the Master Plan Data Viewer (optional) for the class and navigate the data viewer to compare predicted land change under different environmental scenarios, with and without planned projects to slow land loss.

Assign Journal Prompt #6

• Prompt #6: Reflect on today’s lesson about sinking land and sea level rise. How do you think you and your family will respond to the changes brought about as a result of sea level rise? Do you think your life will be affected a lot, a little, or not at all? What feelings come up for you when you think about the future with respect to sea level rise?

Background

Sea Level Rise

Since 1900, sea level has risen between 1 and 2 millimeters per year (10-20 cm per century) on average, which is ten times faster than sea level rise over the previous 3,000 years. Looking into the future, models project the rate of sea level rise will increase, although the amount it will rise largely depends on the amount of warming.

Scientists use averages from a large number of tide gauges worldwide to estimate the global average sea level. Since 1992, global sea level has also been observed using satellite data too, with more accurate results than tide gauges (according to the Intergovernmental Panel on Climate Change AR4 report). Satellite measurements show a rate of sea level rise of 3 mm per year, far more than the tide gauges. Some scientists suspect that the satellite is incorrectly calibrated. Others suspect that the difference may be because the satellite measurements cover much of the globe while tide gauges are near coastlines.

The graph below shows the global mean sea level rise estimates due to melting ice and thermal expansion for four scenarios (according to Parris et al., 2012). Notice that there is a wide range in the scenarios, in part because there are unknowns about how much we will decrease greenhouse gas emissions in the future, and in part because of the possibility of the Antarctic and Greenland ice sliding into the ocean. Notice also that the rate of sea level rise is likely to be non-linear, with an increasing rate of sea level rise over time.

In this lesson, students look at sea level projections for two timeframes (2060 and 2100) to focus on the most vulnerable areas of the coast. You may wish to extend student learning on this topic by having students analyze and interpret the graph above.

How climate change causes sea level rise

There are two ways that a hotter climate leads to sea level rise: (1) as temperatures warm, ice that is on land melts and the water is added to the ocean, and (2) as the water in the ocean warms, it expands. Both are described below in more detail.

Melting Ice

There are between 24 and 30 million cubic km of ice on land. About 90% of this ice is in Antarctica. Most of the remaining ice is in Greenland, and a tiny fraction is locked up in mountain glaciers elsewhere. As global temperatures rise, some of this ice is melting, and the meltwater flows into the ocean, gradually raising sea level. Melting has outpaced snowfall, and the most substantial loss of ice has been on mountain glaciers in the mid-latitudes and tropics and on the Greenland ice sheet.

Additionally, warmer temperatures can cause ice in glaciers and ice sheets to flow faster towards the oceans. In Antarctica, ice is now flowing towards the ocean at a faster rate than in the past. Complete melting of glaciers and ice sheets would raise sea levels worldwide, almost 70 meters (230 feet) above current levels. Of this rise, 7.2 meters would be from the Greenland ice sheet, and 61.1 meters would be from the Antarctic ice sheet. Melting glaciers would add another half of a meter.

For some perspective on all this melting ice, consider this: sea level has risen about 120 meters since the last glacial maximum (approximately 20,000 years ago) when ice covered large parts of the Northern Hemisphere and wooly mammoths roamed the Earth.

Note that melting sea ice, which is ice formed from sea water, has only a very minor impact on sea level since the ice is already in the water.

Thermal Expansion of Seawater

Water expands as it gets warmer, and it is warmed as the climate warms. The amount the water warms is very small, but since there is so much water in the ocean, it expands a lot. Scientists estimate that nearly half of sea level rise is due to thermal expansion of sea water.

For example, suppose 1 liter of water, initially at 20° C, was heated to 21° C. It would expand by 0.021% (see the table of volume and temperature). It would increase in volume by 0.21 milliliters. This tiny increase seems trivial, but the ocean contains about 1,400,000,000 cubic kilometers of water. Even a tiny fractional increase adds up to a very large increase in volume, and hence substantial sea level rise.

The different layers of the ocean (surface layers and deep ocean) are not heated equally. Also, the volumes of the various layers are not the same, nor are their initial temperatures, which affects the rate at which they expand.

• The surface layer of the ocean contains roughly 50,000,000 km³ of water and has temperatures ranging from freezing near the poles to around 30° C in the tropics.
• The mid-ocean, where the thermocline produces the transition from a warm surface to cold deep water, holds about 460,000,000 km³ of water and spans a wide range of temperatures.
• The deep ocean holds the most water, some 890,000,000 km³, but because of its relatively cool temperatures of 4° C or less, it is also less prone to expansion as its temperature rises slightly.

Learn more about the NOAA Digital Coast Sea Level Rise Viewer.

Part 1 Extensions

• Explore the LA-SAFE plan, with and without projects more closely. Ask students to choose one aspect to compare under the different scenarios (medium, low, high) and give a 2-minute presentation about it to their classmates.
• Have each student choose one adult with which to have a conversation about the LA- SAFE Master Plan.
  • Tell students to ask the following questions to their adult:
    • How do they feel about the plan-- do they think it is adequate to provide resilience to your community.
    • Do they see any drawbacks or unintended consequences?
    • If they are unaware of the Master Plan, tell them about it and then ask them to share their first impressions of the plan.
    • Have students write about their conversation. Tell them to describe how they felt about the person’s perspective with regards to the Master Plan.

Credits

This activity was developed for Project Resilience, funded by the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine.