: Here you will find clear descriptions of what you just saw, how they know what they said they knew, why they know it to be trustworthy information. Finally we will ask the question, "So what!" and explore why the information is important.
In this clip from the 1990 presentation “N2O Ecological Approaches to Estimates of Global Fluxes,” Dr. Pam Matson brings her perspective as an ecologist to describe the wiggles in the famous Keeling Curve. She states that seasonal changes in concentrations of atmospheric carbon dioxide represent the “biosphere breathing.” In the curve, the “inhalation and exhalation” of plants shows up in atmospheric CO2 level rise during Fall/Winter, when plant growth slows, and CO2 uptake by plants declines. Decreases of atmospheric CO2 occur in Spring/Summer when plant growth is booming, and CO2 levels drop due to increased plant CO2 uptake. Note that another scientist pauses Dr. Matson to ask for the definition of the term heterotroph.
The data that Dr. Matson references is from Dr. Keeling’s monitoring site at Mauna Loa in Hawaii. The Mauna Loa site is located high on a barren volcano, so there are no nearby plants that might directly impact CO2 levels near the instruments. CO2 is a trace gas, and very sensitive instruments are required to measure it. As a result, the Mauna Loa site initially used detectors created by Keeling himself because there were no existing tools that could effectively make the measurements he sought. To read how CO2 is measured at Mauna Loa today, click here.
It is important to note that peaks and valleys on the graph do not occur mid-winter or mid-summer as one might expect. Because atmospheric CO2 levels continue all through the winter, peaks occur in early spring, just before budburst occurs. Conversely, because high plant CO2 uptake occurs all summer, lowering atmospheric CO2, valleys occur in fall, as plants being to lose their leaves.
Dr. Matson’s explanation of the wiggles in the Keeling graph helps clarify why scientists feel confident that the Mauna Loa instruments successfully measures the concentration of atmospheric CO2. The wiggles represent a seasonal rise and fall of CO2 levels that matches the growing and dormant seasons of the northern hemisphere, which fits the expectations that atmospheric CO2 concentrations will fall when plants are growing rapidly and take up more CO2, and concentrations will rise when many plants lose their leaves in the fall, decreasing photosynthesis and CO2 uptake. Confirming observations against logic or already known facts help scientists determine whether or not their conclusions are reasonable. Scientists using the Keeling curve also draw confidence from the correlation of the Mauna Loa record with other records of CO2 taken by other stations around the world.
Another source of confidence is the correlation of the Mauna Loa Record with other records of CO2 taken by other stations around the world. In the associated graphic from the Scripps Institute for Oceanography, you can see the Mauna Loa (MLO) in comparison to other trends at Point Barrow Alaska (PTB), Lo Jolla, California (LJO), Christmas Island (CHR), Samoa (SAM) and the South Pole (SPO).
The link that Dr. Matson draws between plant activity and the atmospheric carbon cycle provides insight into the deep interrelations between different Earth systems and different fields of science. It illustrates how a combination of individual organisms impact the chemistry of the global atmosphere. Without understanding ecological cycles, the wiggles on the Keeling Curve, an important environmental indicator, would be a mystery.
Reflect on the clip using these questions. Then, record your thoughts in a science journal or discuss them with a friend.
Understanding the Graph:
Considering an updated version of the Keeling Curve (attached), answer the following questions, either with a friend or in a science journal.
Understanding the Invisible: PPM
Parts Per Million
Many scientific measurements of liquids or gases use the unit “parts per million” (ppm). This type of unit is a way of understanding what percentage of a mixture is composed of the element or compound you are studying. For example: if we have one million molecules of a mixture of carbon dioxide, nitrogen, and oxygen and 200 of those molecules are oxygen molecules, then your mixture is 200ppm oxygen.
This activity can either be performed in a large group or with a small set of friends. Observations may be discussed or recorded in a science journal.
Since we cannot see ppm, how can we better understand this type of unit in a way we can sense? By using a gas that we can smell.
Materials: A room where you are allowed to change the room's odor, a stopwatch or clock with a seconds hand, a non-toxic gas (or rapidly vaporizing liquid) with a strong odor that is safe to breathe, e.g. an inexpensive perfume or safe gas recommended by a science teacher. If you are under 18, ask an adult for help.
“The History of the Keeling Curve,” The Keeling Curve. 2013. Scripps Institution of Oceanography: April 3, 2013. http://keelingcurve.ucsd.edu/the-history-of-the-keeling-curve/