Segment 4

This segment describes how the warming effects of carbon dioxide (aka it’s “radiative properties”) were studied by the US Air Force immediately after World War 2, and why the varying orbit of Earth around the Sun drives the cycle of the Ice Ages. Alley demonstrates, through the history of the Franz Josef Glacier in New Zealand, that orbital variations (aka “natural variation”) alone did not make things cooler or warmer: that took the feedback effect of falling and rising levels of CO2.

Annotated Script
Interactive version: panels 29-47
Downloadable PDF: pages 14-22

  • Students will describe how atmospheric CO2 absorbs and emits radiation.

  • Students will examine ice core records and measurements taken at Mauna Loa in Hawaii to observe that the amount of CO2 in Earth’s atmosphere is increasing.

  • Students will observe that scientists use glaciers and ice sheets to study past climate, including past concentrations of atmospheric CO2.

  • Students will describe how variations in Earth’s orbit can influence Earth’s climate but that these variations do not explain the current rise in average global temperature; rising atmospheric CO2 levels are associated with rising global temperatures (and vice versa).

Middle School Global Climate Change


High School    Earth and Solar SystemEarth Materials and SystemsWeather and Climate


Earth and the Solar System
Cyclical changes in the shape of Earth’s orbit around the Sun, together with changes in the tilt of the planet’s axis of rotation, both occurring over hundreds of thousands of years, have altered the intensity and distribution of sunlight falling on the Earth. These phenomena cause a cycle of Ice Ages and other gradual climate changes. (secondary to HS-ESS2-4).

Earth Materials and Systems
The geological record shows that changes to global and regional climate can be caused by interactions among changes in the Sun’s energy output or Earth’s orbit, tectonic events, ocean circulation, volcanic activity, glaciers, vegetation, and human activities. These changes can occur on a variety of time scales from sudden (e.g., volcanic ash clouds) to intermediate (ice ages) to very long-term tectonic cycles. (HS-ESS2-4)

Weather and Climate
Changes in the atmosphere due to human activity have increased carbon dioxide concentrations and thus affect climate. (HS-ESS2-4, HS-ESS2-6) 

Global Climate Change
Human activities, such as the release of greenhouse gases from burning fossil fuels, are major factors in the current rise in Earth’s mean surface temperature (global warming). Reducing the level of climate change and reducing human vulnerability to whatever climate changes do occur depend on the understanding of climate science, engineering capabilities, and other kinds of knowledge, such as understanding of human behavior and on applying that knowledge wisely in decisions and activities. (MS-ESS3-5)

carbon dioxide (CO2), climate change, greenhouse gas, glacial, interglacial, Milankovitch cycles (precession, obliquity, eccentricity), radiation (infrared)

Prior to viewing this segment and conducting the activities below, students should have a basic understanding of Earth’s greenhouse effect along with knowledge that CO2 is a heat-trapping or greenhouse gas. The activities below will help students to understand how CO2 behaves as a heat-trapping gas.
A good description of the greenhouse effect along with a diagram can be found at
Let your students acquire evidence that Earth emits radiation in response to being warmed by the Sun. Show students either thermal infrared images of Earth’s surface or by letting them explore their schoolyard using inexpensive infrared thermometers (perhaps your school’s Facilities department uses IR sensors to check for heat leaks?) to measure the surface temperature of different surfaces/objects.
Ask your students:

  • Why do you think this segment started with a short history of the USAF and heat-seeking missiles?
  • What explains the observation that CO2 molecules in the atmosphere interfere with heat-seeking missiles?
  • To conclude, tell your students that the thermal radiation they observed in the engagement activity is the same kind of radiation used by the heat-seeking missiles featured in the ETOM segment.

1) CONCEPT: CO2 absorbs and emits infrared radiation.

To provide further evidence that CO2 absorbs thermal radiation, explain how a CO2 gas sensor works. The design of a CO2 gas sensor is based upon the fundamental principle that CO2 gas absorbs infrared radiation. For more information read:

ACTIVITY: Where is CO2 found in the atmosphere?

Ask students to predict what they would discover if they took CO2 gas sensors outside into their schoolyard. Would they encounter CO2 at ground level? Where might CO2 levels be higher than average? Lower than average? [Extension] If available, send students outside to answer these questions using a CO2 gas sensor. Encourage students to test a nearby stand of trees/forest, the exhaust from an idling vehicle, etc.

ACTIVITY: How can we see greenhouse gases?


  1. Ask students if they can think of a tool that can be used to visualize a greenhouse gas since these gases are known to absorb and emit infrared radiation.
  2. Show students the short video from the Little Shop of Physics titled, Warm It!

  1. Pause at 0:45 and ask the class to brainstorm the answer to “Why can’t we see

the hot air?” Levels of CO2 in regular air are not sufficient enough to “see” it with a thermal infrared camera.

  1. Ask students where they would go to next to look for CO2 and then finish watching the video clip.
  2. Ask students to reflect on what they learned from watching this video clip.
  3. [extension] If a thermal infrared camera is available, ask your students to explore their schoolyard for sources of CO2 (e.g., exhaust pipe) using a handheld thermal camera (A local energy auditor would have access to a camera – perhaps invite an auditor to discuss how he/she uses such a camera in their work. You can see such a sensor at work in the Kansas and conservation video in ETOM program 3).

These brief, inquiry-based activities can help students understand that atmospheric CO2 molecules absorb thermal radiation.

2) CONCEPT: The amount of CO2 in Earth’s atmosphere is increasing.

ACTIVITY: Carbon Dioxide Trends (grades 6-12)

From “Facing the Future’s” Climate Change: Connections and Solutions (Lesson 2)

Grades 6-8 Curriculum

Grades 9-12 Curriculum

(Short registration may be required to access free curricula)

This activity enables students to interact with data by graphing atmospheric CO2 concentrations from 1958-2004 recorded at Mauna Loa (download data from 2005-2013 here). Students also examine historical CO2 data from ice cores and are asked to predict future CO2 emissions if we don’t reduce emissions/under a “Business as Usual” scenario.

This activity incorporates graphics from Woods Hole Research Center that clearly illustrate the nature of science: that scientific investigations use diverse methods (e.g., atmospheric measurements and ice core data) to answer the same question and that a scientific hypothesis is strengthened when multiple lines of evidence support it (NGSS Connections to the Nature of Science). These graphics can also be found at: (Figures 1 and 3).

3) CONCEPT: Variations in Earth’s orbit can influence Earth’s climate, and have certainly done so in the past, but do not explain the current rise in average global temperature; rising atmospheric CO2 levels in the past corresponded with a rise in global atmospheric temperature (and vice versa). Climate change, in the past, has been entirely “natural” but today there is clear evidence that humans are involved. (See also the ETOM “It’s Us” video segment in Program 1.)


Activity: Milankovitch Cycles (Animations/Online Tutorial)

These animations depict the three major components of the Milankovitch Cycles that impact global climate, visually demonstrating the definitions of eccentricity, obliquity, and precession, and their ranges of variation and timing on Earth. While these cycles are also shown in the ETOM segment, this resource will let students delve deeper into learning about each at their own pace.

Activity: Temperature and atmospheric CO2 levels over the past 400,000 years

The variations in concentration of CO2 in the atmosphere during the last 400,000 years are related to glacial cycles—alternating glacial (Ice Age) and interglacial (warm) periods—most directly caused by the Milankovitch cycles. To see how the Milankovitch cycles impacted Earth’s climate prior to the Industrial Revolution, show your students Figure 1 which depicts data from the Vostok ice core in Antarctica and ask the following:

  • What trend(s) do you notice about CO2 and temperature?
  • What part(s) of the graph depict an Ice Age (glacial period)?
  • What parts of the graph depict a warmer (or so-called “interglacial”) period?
  • What human activities have contributed to CO2 emissions since around 1880?

For high school level, students could directly interact with data from the Vostok Ice Core by conducting the activity, Vostok Ice Core: Excel (Mac or PC) available at:

This segment could further be expanded by asking students to examine the various lines of evidence that show that human activities are to blame for Earth’s current warming trend, many of which are related to content addressed in this segment. has compiled an explanation of these “human fingerprints” and has described them at basic, intermediate and advanced levels.

Content in this segment integrates the Disciplinary Core Ideas cited above to the most directly relevant NGSS Performance Expectations:


Earth and Human Activity

MS-ESS3-5. Ask questions to clarify evidence of the factors that have caused the rise in global temperatures over the past century.


Earth’s Systems

HS-ESS2-4. Use a model to describe how variations in the flow of energy into and out of Earth’s systems result in changes in climate.



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