This activity is part of the Climate Change Challenge unit.
1. Introduce global climate data collection with an encyclopedia article.

  • Prompt students to recall prior knowledge in a Think-Pair-Share by asking:
      • What are some sources of carbon dioxide in our atmosphere?
      • What are some carbon sinks?  
  • (Students' responses will vary, but will likely reflect sources and sinks from the carbon cycle diagram from the Carbon All Around activity.)
  • Given their knowledge of carbon sources and sinks, assign students to predict how carbon dioxide in Earth’s atmosphere has changed recently, and to write this hypothesis in their notes. Ask:    
      • Do you think carbon dioxide levels in our atmosphere have been increasing, decreasing, or staying the same? Why? (Students' hypotheses will vary, but look for the inclusion of reasoning related to the greenhouse effect and carbon cycle.)
  • Distribute copies of The Keeling Curve encyclopedia entry and assign students to read and annotate this article in pairs, previewing the questions for the discussion to follow their reading:
      • What is the Keeling Curve? (A graph representing the concentration of carbon dioxide in Earth’s atmosphere since 1958.)
      • Why does the amount of carbon dioxide increase and decrease a small amount each year? (The amount of carbon dioxide goes up in the winter when there is less photosynthesis and more plant decomposition that releases carbon dioxide (a carbon source). The amount of carbon dioxide goes down in spring and summer, when there is more plant photosynthesis absorbing carbon dioxide.)
      • How does the Keeling Curve help you confirm or revise your hypothesis regarding carbon dioxide levels since 1950? (Students' responses will vary, but should address their hypotheses with updated reasoning, if necessary.)
  • Discuss volunteers’ responses as a class.

2. Engage with an interactive Keeling Curve to compare short- and long-term carbon dioxide trends.

  • Project the SCRIPPS interactive Keeling Curve. Explain that this resource will allow the class to “zoom in” on the Keeling Curve data, asking questions about the amount of carbon dioxide in the atmosphere right now and over time.
      • With students, identify three critical elements of this graph (and others they will encounter in the unit):
          • Title (The title is frequently located above the graph. In this case, it is the current date, followed by “Carbon Dioxide Concentration at Mauna Loa Observatory.”)
          • Axis Labels (The x-axis label is typically found below this horizontal axis. In this case, it is a measure of the time or date. The y-axis label is typically found to the left of this vertical axis. In this case, it is a measure of the CO2 concentration in parts per million (ppm)).
          • Key (if present). (The key helps to distinguish the nature of the data. It shows the meaning of colors or symbols, for example. In this case, the key helps to distinguish between averages taken at different time-scales.)
  • Moving the cursor over the following buttons, ask students to identify the direction of change (or trend) that they see in the data.
      • One week (Students will see daily fluctuations or cycles, but will not see an overall change.)
      • One month (Students may see a slight up or down trend, depending on the time of year.)
      • Six months (Students will see an up or down trend as part of the yearly fluctuation or cycle, depending on the time of year.)
      • One year (Students will see the yearly fluctuations or cycles. Prompt them to note whether the starting and ending points on the graph show a change.)
      • Two years (Students will see the yearly fluctuations or cycles. Prompt them again to note changes in the level of troughs and peaks in the curve.)
      • Full record (Only when the full record is visible is the long-term increase in carbon dioxide obvious).
  • In a Think-Pair-Share, ask students to reflect on the following question:
      • Why is it important for scientists to measure changes in carbon dioxide and the climate over long periods of time? (Changes in long-term processes such as climate must be monitored over similarly long periods in order to accurately measure the trend).

3. Model data analysis across time to support student creation of an evidence-based carbon dioxide level comparison.

  • Distribute the Global Trends Calculation Tracker handout to students.
  • Ask volunteers to recall the meaning of mean, median, and range, using their notes from the Our Greenhouse activity. Record their definitions and any formulas they provide in a visible location.
  • Project carbon dioxide data for 12 months of the first year (1959) in the SCRIPPS Atmospheric CO2 data (use the monthly_in_situ_co2_mlo.csv link under “In situ CO2 data”). Then model calculation of mean, median, and range for the "CO2 [ppm]" data by hand or with a calculator for these 12 months in a visible location in a chart that mirrors Part A of the Global Trends Calculation Tracker.
  • Repeat this step to model calculations with the whole class, using the last full year available in the dataset.
  • Compare the mean, median, and range for these two years, asking students:
      • Are these values different between 1959 and the most recent year? (Yes, they are very different; the values for the current year are much higher.)
      • Does this match what you saw in the Keeling Curve graphs? (Yes, the Keeling Curve graphs also showed this increase over long periods of time.)
  • Assign students to choose two other full years of data for which to compare mean, median, and range, and complete their calculations on Part A of the Global Trends Calculation Tracker.
      • They may wish to compare their birth year with the most recent full year, for example.
  • Next, model how to write an evidence-based claim comparing 1959 and the most recent year. For example:
      • The year 2018 had more carbon dioxide than the year 1959: the mean and median are both over 90 ppm higher for 2018 than 1959, and these differences are much greater than the yearly ranges of only 4.96–5.71 ppm.
  • Prompt students to reflect on the data from their two years of choice, and to write a similar evidence-based comparison of these years in Part B of their Global Trends Calculation Tracker.
  • Revisit the class Know and Need to Know chart, prompting students to consider the connections between carbon sources, carbon dioxide levels in the atmosphere, and global temperatures.

Informal Assessment

Informally assess students’ ability to calculate mean, median, and range of months within years from carbon dioxide data, and to write evidence-based claims comparing years.

Extending the Learning

Step 1: Students can also read the encyclopedia entry Mauna Loa Observatory to gain an additional sense of where and how climate data are collected.

Subjects & Disciplines

  • Earth Science
    • Climatology

Learning Objectives

Students will:

  • Analyze an interactive graph to identify short- and long-term trends.
  • Write an evidence-based claim comparing carbon dioxide levels across years.

Teaching Approach

  • Project-based learning

Teaching Methods

  • Discussions
  • Inquiry
  • Reading

Skills Summary

This activity targets the following skills:

Connections to National Standards, Principles, and Practices

Common Core State Standards for English Language Arts & Literacy

  • CCSS.ELA-LITERACY.RST.6-8.7:  Integrate quantitative or technical information expressed in words in a text with a version of that information expressed visually (e.g., in a flowchart, diagram, model, graph, or table).
  • CCSS.ELA-LITERACY.W.7.1.A:  Introduce claim(s), acknowledge alternate or opposing claims, and organize the reasons and evidence logically.

Next Generation Science Standards

What You’ll Need

Materials You Provide

Required Technology

  • Internet Access: Required
  • Tech Setup: 1 computer per learner, Monitor/screen, Projector

Physical Space

  • Classroom
  • Computer lab


Familiarize yourself with the dataset to be used in this lesson (Scripps Atmospheric CO2 data) before class in preparation to orient and guide students.  


  • Large-group instruction
  • Large-group learning
  • Small-group instruction
  • Small-group learning

Background Information

In recent decades, carbon dioxide in Earth’s atmosphere rose from approximately 315 to over 400 parts per million. The famous graph depicting this increase is called the Keeling Curve, after Charles David Keeling. Dr. Keeling began measuring carbon dioxide concentrations in 1958 at an observatory in Hawaii, and these measurements have continued to this day. Although yearly fluctuations in carbon dioxide concentrations occur as a result of photosynthesis by Earth’s large northern forests, the overall trend shows a marked positive slope.


Mean, median, and range are numbers used to summarize information about groups of observations; for this reason, they are called ‘descriptive statistics.’ To calculate the mean, divide the sum of all observations in a list by the number of observations. To find the median, choose the middle observation in an ordered list, or average the two middle observations if there are an even number of observations. To calculate the range, subtract the smallest observation in a list from the largest. These three descriptive statistics are useful for working with large amounts of data, in particular, to describe and compare the average observation or the spread of observations in two groups.

Prior Knowledge

  • None

Recommended Prior Activities


carbon dioxide

greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

carbon sink

area or ecosystem that absorbs more carbon dioxide than it releases.

carbon source

process, area, or ecosystem that releases more carbon dioxide than it absorbs.


gradual changes in all the interconnected weather elements on our planet.


increase in the average temperature of the Earth's air and oceans.

Keeling curve

graph illustrating the amount of carbon dioxide (CO2) in Earth’s atmosphere as measured at the Mauna Loa Observatory in Hawaii.


mathematical value between the two extremes of a set of numbers. Also called the average.


situated in the middle.


difference between the smallest and largest value in a set of numbers.