What is the Earth's Average Temperature?
Topic: Planetary energy balance: the temperature of the planet vs. the temperature of the earth's surface
Course type: Introductory, non-majors' college level
This activity teaches Climate Literacy Essential Principle 2: Climate is regulated by complex interactions among components of the Earth system
This activity teaches: Concept C - Greenhouse Effect. The amount of solar energy absorbed or radiated by Earth is modulated by the atmosphere and depends on its composition. Greenhouse gases— such as water vapor, carbon dioxide, and methane— occur naturally in small amounts and absorb and release heat energy more efficiently than abundant atmospheric gases like nitrogen and oxygen. Small increases in carbon dioxide concentration have a large effect on the climate system.
GoalsStudents should be able to do the following:
- Estimate the average temperature of the earth as a whole (atmosphere and surface combined), by applying several basic physical principles to satellite observations of solar energy.
- Compare this temperature to the global average temperature of the earth's surface.
DescriptionThis short, pedagogically flexible activity (Microsoft Word 2007 (.docx) 516kB Jun15 11) guides students to answer six questions about the radiative energy budget of the earth as a whole. The activity gives students practice applying basic physical principles to observations and raises a question that can motivate investigation of the greenhouse effect.
(a) the concept of a balanced (energy) budget;By applying these principles, students can determine the temperature that the earth must have to create the observed, nearly balanced planetary energy budget.
(b) a basic law of radiation ("the warmer an object is, the more radiation it emits"); and
(c) satellite observations of radiation.
Students then contrast this planetary temperature with the global, long-term average temperature of the earth's surface, which raises the question of why the surface is so much warmer than the planet as a whole. Investigation of the greenhouse effect in subsequent activities can resolve the apparent discrepancy.
The activity can be implemented pedagogically in any of a variety of ways, such as in-class, small-group collaborative problem solving; out-of-class individual homework; pre-class, online assignment, etc. Most of the questions can be implemented at least partly as multiple choice questions if desired, for use with clickers in class, for example.
Activity: What is the Earth's Average Temperature? (Microsoft Word 2007 (.docx) 516kB Jun15 11)
Blackbody Radiative Emission vs. Temperature (Excel file) (Excel 2007 (.xlsx) 57kB Jun15 11)
The answers to the six questions posed in the activity are straightforward. Students can turn in their responses in written form (paper-based or online, in class or as homework). Alternatively, most of the questions can be posed as multiple choice questions for use with online quizzes or clickers in class. As a very basic follow-up, students should be able to describe the fundamental property of an object that changes when an object absorbs more radiant energy than it emits. [i.e. the temperature...and it must increase].
Connections to other Activities
This activity is one of a suite of five activities designed to address the concepts that address how the greenhouse effect influences global temperature (Principle 2, Concept C) which can be used individually or combined as desired.
This activity can be used as a warm-up for a variety of investigations of the greenhouse effect and global warming. One example is The Greenhouse Effect: Why is the Earth's Surface So Much Warmer than the Earth as Seen from Space?, a complementary activity in which students apply the same physical concepts used here to analyze energy budgets for the atmosphere and for the earth's surface. The intent is to help students understand better how the greenhouse effect works and how enhancing the greenhouse effect leads to global warming.
Earth's Global Energy Budget ( 1.1MB Jun15 11), Kevin Trenberth, John Fasullo, and Jeffrey Kiehl, March 2009, Bulletin of the American Meteorological Society (PDF file)
More on this topic from CLEAN
How to teach with this principle from the CLEAN site
See CLEAN reviewed activities for teaching about Greenhouse Effect