Atmospheric carbon dioxide (CO2) levels have been changing globally since about 1785. Ice core samples indicate that prior to the late 1700s, CO2 levels were around 280 parts per million (ppm). In 1885, CO2 levels peaked at 293 ppm as a direct result of the Industrial Revolution, a period powered by coal combustion. As industrialization continued worldwide to include fossil fuel cars and electric power plants, CO2 levels rose to 349 ppm. In 2014, CO2 levels reached 400 ppm, and today, atmospheric levels are hovering around 416 ppm.
Carbon dioxide levels are often associated with climate change, but this is just one piece of the puzzle. How are changing atmospheric CO2 levels impacting the cycling of carbon in the hydrosphere, geosphere, and biosphere? One method used to examine the interactions between atmospheric carbon dioxide and the biosphere is to measure global leaf cover. Since plants absorb CO2 from the atmosphere during photosynthesis, it can be hypothesized that as CO2 levels increase, leaf cover should increase. Using satellite imagery, scientists can study the relationship between atmospheric carbon dioxide and global leaf cover (as seen in the map below).
In this activity, students use data from 2015 through 2020 to build on the model shown in the map below. They are asked to modify the model presented for 2015 to explain predicted leaf cover for 2016, 2018, and 2020 after calculating percent change in atmospheric carbon dioxide levels.
Look at the image below. The scale indicates percent change in the amount of leaf area worldwide from 1982 to 2015. What patterns do you notice?
PE HS-ESS2-6. Develop a quantitative model to describe the cycling of carbon among the hydrosphere, atmosphere, geosphere, and biosphere.
PE HS-ESS3-6. Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.
No PPE is required for this activiy.
Copy or upload the student activity sheets.
1. Based on the global CO2 levels from 2015 to present, construct a graph of CO2 levels in parts per million (ppm).
2. Calculate annual average and percent change for each year from 2015 to 2020.
3. Using your data for percent global CO2 change in parts per million since 2015 as a starting point, construct a global leaf cover model for 2016, 2018, and 2020. Each year, CO2 increases, so the shade of green should darken indicating more leaf area. What were shades of yellow, students may change to green.
Use the historical and current data to propose a model for the cycling of carbon through changes in atmospheric CO2 levels and global leaf cover. Your model may be a graphic, flow chart, or written explanation.
Student answers may vary, but key points include the following: as atmospheric CO2 increases, more CO2 is available to plants for photosynthesis, more photosynthesis means more leaf production, and more leaf production means more global leaf area, which means a greener planet.
Compare your model to the one described in the 2016 article “Carbon Dioxide Fertilization Greening Earth, Study Finds,” which represents changes from 1982 to 2015. Are the models consistent for explaining the phenomenon of leaf cover change? Explain.
Student answers will vary, but student models should show darker shades of green as CO2 levels increase.
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