3.3: Future Forcings
How are the carbon cycle and humans a part of future climate?
In Lesson 3.2, you used the Carbon Connections climate model to compare forcings on Earth's temperature the past 30 years (1979-2010). You tested how four forcings explained most of the temperature record. There are several other possible factors, but the four forcings you used are the best predictors of temperature.
But what does the future hold for Earth's climate? To answer this, scientists use models to make predictions. The models consist of a grid of cells surrounding Earth, similar to the image above. The models determine the transfer of energy and matter among neighboring cells by different physical processes. Using models like this is one vital way to learn what the future might be like.
You will start Lesson 3.3 by summarizing some results from the Carbon Connections climate model. In particular, in this lesson you will see that:
Energy-use monitors help you and your class see how to conserve energy and reduce carbon emissions.
Did you get to show the Carbon Connections climate model to someone in your family? Perhaps they were interested in the climate model and forcing by volcanic aerosols, or perhaps one of the videos of the Sun. Before you consider what might happen in the future, it is good to summarize important things you saw with the climate model. Here are some key points.
First, climate variability tells how much the temperature goes up or down over several months or years. A system can have a lot of variability, yet also have no change in the average. Think of a swing or pendulum. These vary in a back-and-forth manner, but their average position is always the middle. Similarly, the variability of solar cycles is predictable. Solar radiation increases and decreases. In contrast, the El Niño/La Niña cycles show a lot of variability, but when the peaks and valleys occur is less predictable. Volcanic eruptions are even less predictable. These natural forcings lead to variability in temperature.
Second, a key question is whether the Earth's temperature is changing or staying the same. If overall temperature were increasing or decreasing over many years, that would be climate change. Scientists work to tell between climate variability on the scale of years (e.g., El Niño/La Niña cycles), versus climate change over decades. The data you saw in Lesson 3.1 showed a pattern of increasing temperatures, particularly the past 30 years. In Lesson 3.2, the climate model let you test which factor caused that temperature increase. It was the anthropogenic part. In contrast, the "natural" parts of climate variability (that is, solar cycles and El Niño/La Niña cycles) did lead to a net temperature increase over time.
NASA has a short video called "Taking Earth's Temperature" that illustrates some ways that they are working to monitor Earth's climate. Read the questions below and then watch the video.
You used one kind of climate model to test climate forcings on Earth's temperature. This model connected increases in CO2 levels in the atmosphere to humans. But you also know from Units 1 and 2 that natural processes also lead to changes in CO2 in the atmosphere. So, how can you test the size of the natural and human processes on the carbon cycle?
At the University of Wisconsin, Professor Galen McKinley has used another kind of model to study the carbon cycle and climate. Her model estimates CO2 levels and temperatures in the future. The trends in CO2 level depend on changes in carbon sources and sinks in the carbon cycle. You studied in Units 1 and 2 processes that change the amount of carbon in the atmosphere. Some processes were related to humans, and others were natural. You will use Professor McKinley's model in the steps below to test the relationship between carbon and climate in the future.
Several key processes affect the total CO2 levels in the atmosphere. In the model, two carbon sources add CO2 to the atmosphere, and two carbon sinks remove CO2 from the atmosphere.
The Global Carbon Budget (University of Wisconsin-Madison)
The left graph shows trends in carbon sources and sinks. The right graph shows projections for CO2 in the atmosphere and global temperature. In the left graph, carbon sources have values greater than zero because carbon is added to the atmosphere. Carbon sinks have values that are negative because carbon is subtracted, or removed, from the atmosphere.
Orange parts of the lines show data from 1960 to 2010. The y-axis is petagrams of carbon per year (Pg C/yr). A petagram is a lot of carbon—in fact, one petagram equals 1,000,000,000,000,000 grams of carbon (that is, 1x1015 grams of carbon). How big is that?! Well, imagine that you had some water. One gram of water is about the size of a sugar cube. But one petagram of water would cover a football field (plus end-zones) with water to a depth of 187 km. That's water 120 miles deep, or about 12 times higher than most of the atmosphere!
In the model, each source or sink has a green curve when you select it. The curves go from 2010 to 2100 and show a set of points. When the curve is selected, you can grab and adjust its trend to simulate different scenarios. You will test some scenarios below. Then, under "Controls," you run your projection to 2100, or reset it to the initial values.
If you are unable to see the interactive, click here to open it in a new tab.
In Carbon Connections, you have been able to test different kinds of models and interactives. Some have been hands-on, and others have been on a computer. With both of these, you can see a response to an input. At the same time, it is not always as easy to understand how these models for Earth relate to you, your family, and the things you do every day.
The investigations you did in Units 1 and 2 with the energy-use monitor help you see how you can monitor and possibly change your energy use. Electrical energy for humans to use, on average, involves adding carbon to the atmosphere. If you can identify easy ways to use less electrical energy and lower your energy use, you emit less carbon. If many students like you do the same, you all can make a difference.
Home Energy Use Activity
In Units 1 and 2, you used the energy-use monitor. You looked at energy use from different kinds of light bulbs, as well as things in your classroom and school. But what about your home? That's where your family can reduce their energy use. Using less electrical energy means less carbon emissions, and savings to your family on your energy bill.