Human Energy Systems | Activity 6.2

Tell students in this unit we have been examining how and why carbon emissions are increasing in our atmosphere. But what is that doing to Earth’s systems?

• Open the 6.2 How Our Decisions Affect the Earth’s Future PPT and display slide 3. Remind students of the systems they studied in Lesson 3 of this Unit.
• Use slide 4 to review how rising atmospheric CO₂ intensifies the greenhouse effect and increases global temperatures, which in turn lead to sea level rise and decreases in Arctic Sea ice.
• Use slide 5 to explain that if we could lower CO₂ emissions then we could also have an impact on global temperature rise, sea ice melt, and sea level rise.
• Use slide 6 to review what students learned from using the Simple Climate Model in Activity 6.1. (1) If CO₂ emissions stay constant at current levels (about 10 GtC/year) atmospheric CO₂ (and thus temperature) would continue to increase, and (2) we would have to significantly decrease CO₂ emissions in order to stop the upward trend of atmospheric CO₂.
• Use slide 7 to review the imbalance in carbon pools and introduce the driving question: What will happen to Earth’s systems if we don’t reduce carbon emissions?

Review the IPCC climate model graph from Activity 6.1 to discuss how our decisions affect future temperatures.

Ask: How will our decisions about future CO₂ emissions affect global temperature?

• Students should recognize that the blue lines represent global temperatures if we decrease CO₂ emissions and the red line indicates predicted temperatures if we continue to increased CO₂ emissions at the current rate.
• RCPs: representative concentration pathways
• Remember, that many scientists recommend that we not allow the climate to warm more than 2°C (which will require decreasing CO₂ emissions from current levels).
• Check to make sure that students understand that the blue lines represent scenarios in which people change their behaviors related to fossil fuel usage to substantially reduce CO2 emissions (drastic and quick reduction for RCP2.6 and more gradual but very substantial reduction for RCP4.5). The red line (RCP8.5) shows what would likely happen to global temperature if CO2 emissions continue to increase as they have in the past.
• Ask: What do you think the shaded areas around each line represents? Shaded areas represent uncertainty around the projections. Models about the future are based on long-term trends in the past and our current understanding of how Earth’s systems interact with each other. Therefore, predictions have a certain level of uncertainty around them.
• Notice that the greatest uncertainty is around the highest emissions scenario. This is because scientists are less certain about how Earth’s systems would respond to drastic increases in atmospheric CO₂ (e.g. how much CO2 would dissolve in the ocean and at what rate, how feedbacks such as decreased reflection of solar radiation from ice would speed up warming, etc.)

Use slide 9 to discuss the computer models for sea ice extent.

• Use slide 10 to discuss the computer models for sea level rise.
• Notice that even if CO₂ emissions are drastically reduced, models predict that sea ice will continue to decline and sea level will continue to increase.
• The IPCC 5^th Report states, “Sea level will continue to rise for centuries, even if GHG [greenhouse gas] concentrations are stabilized, with the amount of rise dependent on future GHG emissions.”

Use slide 11 to explain: The decisions that we make as individuals and as communities and nations that affect CO₂ emissions will determine future global temperatures, amount of sea ice, and sea level. Ask: What impacts would increased global temperatures and sea level and decreased sea ice have on us and on other living things? Have students discuss this question with a partner and then share out their ideas.

• Use slide 12 to remind students that they have learned a lot about the causes of climate change in this unit but have only begun to scratch the surface of how it will affect humans and other living things and what we might choose to do mitigate climate change. These questions suggest ways that you may decide to extend the learning.

If you decided to use the Big Idea Probe: What Would Happen if We Cut Fossil Fuel Use in Half?, have students complete it and share their ideas again. Have students discuss how their ideas have changed throughout the unit. See Assessing the Big Idea Probe: What Would Happen if We Cut Fossil Fuel Use in Half and Using Big Idea Probes for suggestions about how to use the Big Idea Probe.

Show Slide 13 of the 6.2 How Our Decisions Affect the Earth’s Future PPT.

• Have students take out their Learning Tracking Tool from the previous lesson.
• Have students write the activity name in the first column, "2 How Our Decisions Affect the Earth’s Future."
• Have a class discussion about what students figured out during the activity that will help them in answering the lesson driving questions:
• What causes the annual cycle: CO₂ concentrations in Hawaii to go down every summer and up every winter?
• What causes the long-term trend: CO₂ concentrations to go up every year?
• How can we predict what will happen to CO₂ concentrations in the future?
• When you come to consensus as a class, have students record the answer in the second column of the tool.
• Have a class discussion about what students are wondering now that will help them move towards answering the unit driving question. Have students record the questions in the third column of the tool.
• Have students keep their Learning Tracking Tool for future activities.
• Example Learning Tracking Tool