Carnegie Mellon University

Introduction to Climate

Last Updated: August 18, 2013

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The greenhouse gas effect is natural and keeps the Earth from being freezing cold.  The natural levels of water, carbon dioxide, and other greenhouse gases in the atmosphere cause the greenhouse effect to influence the temperatures on the earth’s surface substantially. Without this natural greenhouse effect, the Earth would be much colder than it is today (~0°F), and life forms on the planet would be very different.

Almost everything we do directly or indirectly releases greenhouse gases into the environment.  Man-made greenhouse gases have been and still are building up in the Earth’s atmosphere. The Earth’s atmosphere is like a bathtub. There is a faucet (manmade and natural processes) putting water (greenhouse gases) into the bathtub (the atmosphere).  There is also a drain (natural processes) removing the water.  Currently, mankind’s activities are putting more water in the bathtub than the drain can handle, thus filling the bathtub.

Man-made greenhouse gases cause man-made climate change, which is a serious problem that harms everyone on the planet. We have already seen the effects of increased water in the bathtub - there is clear evidence that the sky-rocketing levels of greenhouse gases in the atmosphere do harm. Over the last century, man-made climate change has warmed our planet 1-2ºC. This seemingly small temperature increase has already contributed to worldwide problems including more severe storms, sea level rise, droughts, increased heat-related deaths, and changes in the growing season. Scientists expect another 4-8ºC by the end of the century, leading to changes including severe natural hazards, widespread crop failure, drinking water shortages, significant changes in ecosystem regimes and related industries, and new health problems. If the water spills over the bathtub’s edge - the Earth will be so hot that the natural balance between the atmospheric conditions and today’s forms of life would be destroyed. In that case, there will be radical changes to life as we know it. It is impossible to know what such a world would look like.

Even if we stabilize emissions now, concentrations will increase and temperatures will get warmer throughout our lifetime before eventually stabilizing.  The relation between greenhouse gas emissions (water entering the bathtub), greenhouse gas concentrations (water in the bathtub), and sequestered greenhouse gases (water leaving via the drain, a.k.a. sinks) is very complicated.  How long the current natural sink will be maintained is a matter of speculation. Some sinks have a fixed size, and will eventually fill up. Other sinks absorb a fixed fraction of atmospheric concentrations, thus absorbing more greenhouse gases as concentrations increase. There are a few processes that may become sinks as concentrations increase. Generally speaking, if we stabilize emissions at current levels, the greenhouse gas concentrations will continue to increase within our lifetime because the current sink capacity is smaller than our emissions. Eventually, long after we are all dead, the Earth will reach a new equilibrium where capacity of sources and sinks will be equal. It is unknown if under that equilibrium, Earth will still be inhabitable.

Over a century of man-made emissions are in the atmosphere, and today’s emissions will last for another century. Emitted carbon dioxide (CO2) has a lifetime of (lasts for) longer than a century in the atmosphere. Therefore, we need to reduce CO2 emissions by a much greater percentage than the reduction in concentration needed. In fact, we need to reduce CO2 emissions by 80% to stabilize concentrations within our lifetime. While other greenhouse gases may have different lifetimes, the concept remains the same – many greenhouse gases emitted today will be around for many decades to come.

Developed countries such as the United States are responsible for most of current carbon dioxide concentrations. Current concentration levels of carbon dioxide reflect aggregated emissions from the past century. The United States and other developed countries entered the Industrial Revolution and started polluting over a century ago, while developing countries such as China and India are only now beginning to contribute significant emissions. Even though today China emits more greenhouse gases than the United States, only 9% of the current greenhouse gas concentrations are attributable to China compared to 25% that are attributable to the United States.

There is no silver bullet; to solve this problem, we need both improved technology and lifestyle changes. We will have to put more money into research to find engineering solutions AND we will have to change our behavior to achieve stability. Unfortunately, these changes can be slow and expensive.   To have a significant combined impact in the next few decades, we need to work on BOTH environmentally friendly lifestyles and technologies.


Students will be able to:

  • Explain the greenhouse effect, energy balance, carbon cycle, keeling curve
  • Explain the different sources of greenhouse gases
  • Explain climate change impacts and regional differences
  • Explain what “adaption” is

Materials Needed

  • Water
  • Two large bottles with lids
  • Lamp
  • Alka Seltzer
  • Digital Thermometer
  • 2 clear cups
  • Ice water
  • Powerpoint Presentation: “Climate Presentation” [pptx] [pdf]

Safety Concerns



  • Greenhouse effect: Thermal radiation (heat) from the planet is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions.
  • Greenhouse gas (GHG): A gas in an atmosphere that absorbs and emits radiation within the thermal infrared range (heat). The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.
  • Keeling curve: A graph which plots the ongoing change in concentration of carbon dioxide in Earth's atmosphere since 1958. It is based on continuous measurements taken at the Mauna Loa Observatory in Hawaii begun under the supervision of Charles David Keeling.
  • Power: describes how much energy can be produced in a given time.  Also to supply a device with electricity; the product of voltage and current.  A common unit of measurement is a watt (W); also measured in watts, kilowatts, megawatts, etc.
  • Energy (physics): the capacity of something to do work; an amount.  Measured in watt-hours, kilowatt-hours, megawatt-hours. A typical American household used 940 kWh per month in 2011.


Activity 1: Student Discussion on Climate Change

Time: 5 minutes


  1. Ask the students what they think climate change is, and what they think will happen as a result of climate change.

Activity 2: Experiment

Time: 10 minutes

Supplies: Water, two relatively large bottles with lids, lamp, alka seltzer, digital thermometer


Set up the greenhouse gas experiment and demonstration and hypothesis.  Note: the experiment should be practiced beforehand.

  1. Fill two identical bottles with an inch or two of water. The water should be deep enough to insert the tip of a thermometer. The water in each bottle should be the same volume and the same temperature.
  2. Add an Alka-Seltzer to ONE of the bottles, cap them both tightly, and leave them under a lamp. Be careful to give both bottles equal exposure to the bulb, meaning one should not be blocking the light to the other, and they should be the same distance from it.
  3. Wait. How long depends on the bottles, amount of water, and the lamp, so test this beforehand.
  4. Measure the water temperature in both bottles. As the CO2 emitted from the Alka-Seltzer helped to trap the heat from the lamp, the water in that bottle should be warmer. Note that removing the lids too early to check the temperature will result in some gas escaping, likely making the experiment impossible to continue.

If it doesn't work: The importance of the water is simply to have something that can easily be measured by a thermometer. Having too much of it can make the experiment fail because a large amount of water might be able to absorb all the heat from the lamp without changing a measurable number of degrees. Or, try leaving the bottles under the lamp longer, or use a hotter lamp.

Activity 3: Full group

Time: 15 minutes

Supplies: Powerpoint Presentation: “Climate Presentation” [pptx] [pdf]


  1. Explain the earth’s energy budget and balance from slide 2 of the Powerpoint.
    1. Show that the Earth’s energy comes from solar radiation via the energy balance In = Out
    2. Make the point that climate change occurs when either side of the energy balance is perturbed.
  2. Explain the greenhouse effect from slide 3 of the Powerpoint.
  1. Explain the major concept that there is a difference between surface temperature / radiation and Earth’s effective temperature / radiation.

Activity 4: Full group

Time: 10 minutes

Supplies: Powerpoint Presentation: “Climate Presentation” [pptx] [pdf]


  1. Explain what a greenhouse gas is and how they differ from slide 4.
    1. Show the diagram and explain that how the sources of each gas are primarily how they differ. This will be clear on slide 5.
  2. Explain what the carbon cycle is from slide 6.
    1. Show, with the diagram, how any increase in carbon, from any source, will change the amount of carbon in the atmosphere, increasing atmospheric temperature.
  3. Discuss the Keeling Curve on slides 7 and 8. 
    1. Show what a Keeling Curve is on slide 7, and show that the CO2 levels have passed the 400ppm threshold on slide 8.
    2. Mention that this is the first time the CO2 levels have reached 400ppm in an estimated 3 million years.

Activity 5: Full group

Time: 10 minutes


Results of GHG experiment/group discussion on implications

Activity 6: Full group

Time: 5 minutes

Supplies: 2 clear cups, ice, water


Start the discussion with two glasses of water- one with a few pieces of ice and then filled with water and the other with enough ice to overfill the glass and then filled with water. Conduct a survey of what students think will happen as the ice beings to melt in each glass- will the water level decrease, remain the same, or will the glass overflow?

Activity 7: Full group

Time: 15 minutes


What are possible climate change impacts, what are their effects? Variability by location Try to get their ideas first as a springboard; Impacts in real time (slides 10,11,12)

Activity 8: Full group

Time: 5 minutes


Feedback loops (albedo, methane in permafrost) (slide 14)

Activity 9: Full group

Time: 15 minutes


Adaptation – what is it, why is it important, case study of the northeast (slide 13)

Activity 10: Full group

Time: 5 minutes


Observe what happened to the water level in the glasses (slide 15) (sea ice vs glacial melt discussion)

Additional Resources


NASA. “The Carbon Cycle.” NASA Earth Observatory. 16 Jun 2011. Web. 29 Jul 2013. <>

NASA’s page on the carbon cycle shows the different sources of carbon into the atmosphere, and how changing those sources affects the overall balance.

Pennsylvania State University. “Greenhouse gases and the Keeling Curve.” Penn State College of Earth and Mineral Sciences. Web. 26 Jul 2013. <>

The Penn State page explains the science behind the greenhouse effect in a simple manner, including a diagram. It also introduces the Keeling Curve with a video walking the user through its history, and how the chart is read.

United States Environmental Protection Agency. “Global Greenhouse Gas Emissions Data.” United States Environmental Protection Agency. 9 Jul 2013. Web. 26 Jul 2013. <>

The EPA page on greenhouse gas emissions analyzes the amount of gases emitted of each type, by a number of different sources, and by country. It also identifies trends in overall CO2 emissions.

United States Environmental Protection Agency. “Greenhouse Gases: A Student’s Guide to Climate Change.” 18 Jul 2013. Web. 26 Jul 2013. <>

The EPA’s interactive student guide simply explains what greenhouse gases are with the help of numerous colorful, well-diagramed graphs. | NOAA.  URL [accessed Aug. 25, 2013]:

Fifth Assessment Report (AR5) | Intergovernmental Panel on Climate Change (IPCC). URL [accessed Aug. 25, 2013]:

MIT’s Greenhouse Gas Simulator | NOAA URL [accessed Aug. 25, 2013]:

National Climate Assessment | US Global Change Research Program. URL [accessed Aug. 25, 2013]:

National Geographic (2009): The Big Idea: The Carbon Bathtub. URL [accessed Aug. 7th, 2013]:

Opinion / Newspaper

Evers. “Arno A. Evers FAIR-PR.” Web. 26 Jul 2013. <>

The EVERS page shows a diagram of the Earth’s energy balance, and quantifies the amount of energy emitted by the sun as well as the amount of energy used.

The Greenhouse Effect and the Bathtub Effect | Dot Earth. URL [accessed Aug. 25, 2013]:

The Forum on Religion and Ecology at Yale | Yale. URL [accessed Aug. 25, 2013]:


Lesson idea from Alex Loewi;  final product compiled by Sabrina Larkin on behalf of the Leonard Gelfand Center for Service Learning and Outreach.

Funding Sources

Portions of this work were supported by a) the Leonard Gelfand Center for Service Learning and Outreach, and b) the Center for Climate and Energy Decision Making (SES-0949710) through a cooperative agreement between the National Science Foundation and Carnegie Mellon University.

Next Generation Science Standards Alignment

HS-ESS3-4: Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

Crosscutting Concept: Stability and Change

HS-ESS3-5: Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth systems.

Crosscutting Concept: Stability and Change