2.3: The Breathing Biosphere
How can simulations and models help you understand the annual breathing of the biosphere?
In Unit 2, you are exploring carbon that is moving through the Earth system. After an aquarium experiment, you are now thinking about systems as big as Earth. Photosynthesis and respiration are key natural processes in the carbon cycle. Factors such as the amount of sunlight can limit or control how fast those processes act.
Another way to explore Earth's moving carbon is with models and simulations. That is what scientists do; it helps them test forcings and responses. In this lesson, you will use models of CO2 levels in the atmosphere to understand the processes that move carbon. You will also be able to compare the natural processes with the human influence. In Lesson 2.3, the main learning goals are:
As you continue with this lesson, use the focus question to guide your learning.
Maybe you've heard the idea to "plant a tree" to reduce CO2 in the atmosphere. This may be true if only trees did photosynthesis; however, all organisms, including you and plants, also respire CO2 to the atmosphere. If the biosphere has both processes, what is the net change in CO2 in the air around them? In this lesson, you will answer this question by using a model.
You can think of carbon in the atmosphere like a bank account. If you put money in, your bank balance increases. That is a positive flow of money. When you take money out, your balance decreases. That is a negative flow of money. A useful term in systems-thinking is the net flow. The net flow is the sum of the amount in and the amount out. If more money is leaving your account than is entering, the net flow is negative. It may be time for some saving! Similarly, carbon moves into and out of the atmosphere.
You can think of the atmosphere as a carbon account. Start accounting for the effect of living things on carbon with the following steps. Do the first two steps below as a class, and then continue on your own with the Carbon Flux interactive.
Mauna Loa is a volcano on the Big Island of Hawaii. In Lesson 2.2, you started learning about CO2 measurements there. At nearly 14,000 feet (about 4,200 m), it rises into the atmosphere near the middle of the Pacific Ocean. Besides telescopes for astronomy, Mauna Loa is home to a research station that has measured CO2 in the atmosphere for more than 50 years. These data are like the CO2 data from air bubbles in the Antarctic ice core in Unit 1. An important difference is that Mauna Loa has recorded values for each month.
Recall that air arriving at Mauna Loa has crossed the Pacific Ocean. Scientists can trace the path of the air through Europe and Asia. Air travels to Mauna Loa from these regions in a few weeks. When that air arrives, the CO2 signal is a record of photosynthesis (P) and respiration (R) from wherever the air has been—mid‐latitudes in the Northern Hemisphere.
In the following steps, you will use a model to simulate changes in CO2 in the air from photosynthesis and respiration. Using models like this helps scientists better understand carbon sources and sinks in the carbon cycle.
In section B, the data were only for changes in CO2 from natural processes: photosynthesis and respiration. The trade-off between these makes it look like the biosphere is "breathing" each year.
What other factors affect the CO2 in your air? From the title of this section, it comes from human activities. The graph shows the actual CO2 data measured at Mauna Loa for the period 2004-2010. The total curve has natural and human effects. By comparing the two graphs, you can see the difference by adding the contribution by human activities.
Analyze these data further in the steps below.
If you are unable to see the interactive, click here to open it in a new tab.
Complete Lesson 2.3 with the following questions.
The Green Machine
Earth is quite a sight from space. A main feature you see is oceans, as about 70 percent of Earth's surface is covered in oceans. You also see a lot of clouds. Between the clouds and oceans, you can see some areas of green and tan. The green regions have many plants and other photosynthesizing organisms.
But you've also seen that a lot of photosynthesis and respiration also occurs in the oceans. In fact, about one-third (33 percent) of photosynthesis occurs in oceans. Even though the oceans look blue, they harbor lots of photosynthesizing organisms. These producers are the base of the marine food web. Thus, in considering both land and oceans, Earth is a "Green Machine."
Listen to your teacher for directions on watching The Green Machine video. You may have time to view it at the end of class, or on your own. In Lesson 2.4, you will think more about how humans affect the green machine.