This activity by the Royal Society of Chemistry looks at the greenhouse gas effect on climate change taking into account the increase in temperature and carbon dioxide concentration in the atmosphere. Also included is a study of some of the other gases which contribute to the greenhouse effect and a description of how molecules interact with radiation.
Students will learn how greenhouse gases are contributing to global warming and specifically, how carbon dioxide is fueling the increase in temperature of the globe.
ACTIVITY DESCRIPTION AND TEACHING MATERIALS
This lesson should take about four hours of class time. It includes material for lectures about climate change and greenhouse gases, including descriptions and figures.
The greenhouse effect and global warming
This PDF covers the greenhouse effect from a chemical perspective by looking at how molecules interact with IR radiation.
greenhouse gases effect and global warming.pdf
Climate change and carbon dioxide
This resource includes a brief description about the relationship between changes in climate and concentration of carbon dioxide in the atmosphere.
climate change and carbon dioxide.pdf
CO2 is not the only greenhouse gas
CO2 is not the only greenhouse gas causing climate change; there are many other gases that play an important role. This PDF explores the effect of these other greenhouse gases.
greenhouse gases other than CO2.pdf
TEACHING NOTES / CONTEXT FOR USE
Fairly stable temperatures and climates are reached when the amount of radiation coming into the atmosphere is equal to the amount of radiation escaping from the atmosphere, referred to as a steady state. The sun emits radiation in a variety of different forms including ultraviolet (UV), visible, and also infrared (IR) radiation. When radiation reaches the Earth, some of it is absorbed by the Earth causing the temperature to increase. IR radiation is mainly absorbed by water vapour in the atmosphere and contributes to the warming of the Earth. UV radiation tends to break bonds due to its very energetic nature.
The energy of each type of radiation is important in order to better understand the effect each has on a molecule. Molecules can absorb radiation. When molecules absorb radiation, the energy of the radiation causes electrons to be excited to a higher energy state. When a bond is broken, an electron that was originally helping to create the bond is excited. The bond is very low in energy so a lot of energy is required to move the electron from the bond to a higher state. This is why UV radiation may result in bond fission; it is extremely energetic. IR radiation is less energetic so rather than breaking bonds, it causes them to vibrate. Advanced theory shows that a molecule will absorb IR radiation if the vibration causes a change in dipole moment. Consequently, nitrogen and oxygen gases are not IR active, but many of the gases present in the atmosphere in lower concentrations such as water vapour and carbon dioxide are.
Anthropogenic emissions are man-made emissions. These emissions change the composition of the atmosphere by increasing the amount of naturally occurring gases, such as carbon dioxide and methane, and also by introducing gases that do not naturally occur, such as CFCs (chlorofluorocarbons). It is important to differentiate between the natural greenhouse effect, which is essential for life to exist, and the enhanced greenhouse effect. The enhanced greenhouse effect is caused by anthropogenic emissions and is generally thought to be the cause of global warming.
While carbon dioxide seems to have the greatest impact on climate, it is not the only important greenhouse gas. Actually, on a molecule for molecule basis it has a much smaller effect than most other greenhouse gases. Two measures are used to determine the relative effects of the different gases – radiative forcing and global warming potential (GWP). Radiative forcing is a measure of the change in the earth’s energy balance caused by a given substance. This takes into account the amount of gas which is present in the atmosphere. Global warming potential is a measure of global warming which would be caused in a 100 year span by an instantaneous (or pulse) emission of a gas relative to carbon dioxide, which is given the arbitrary value of 1. This measure takes into account the lifetime of the gas in the atmosphere.
The so-called ‘super greenhouse gases’ have very long lifetimes (giving them large global warming potentials) and are accumulating in the atmosphere at a high rate. Most of the super greenhouse gases contain fluorine. These compounds absorb IR radiation in a unique energy ‘window’ causing them to have an even greater impact on global warming.
In order to test what the students have learned, there are questions provided in the PDF file. Some questions may require conceptual knowledge while others require imagination based answers. For some questions, it is better if students divide themselves into groups. Another important discussion topic is the application of chemistry to greenhouse gases in order to forecast climate change.
REFERENCES AND RESOURCES
An introduction to how climate change is related to greenhouse gases.