STUDENT INSTRUCTIONS

Part 1
There are several gases produced by human activities that contribute to climate change. Carbon dioxide (CO₂) receives the most attention in the media, but other gases are also very important contributors to climate change. In this activity, we'll specifically examine methane (CH₄), including its relative importance for climate change and why it is increasing in the atmosphere.

Table 2 shows carbon dioxide and methane abundance in the atmosphere, as well as the percent increase for each gas since pre-industrial times. Concentrations of the two gases are reported in parts per million (ppm), which indicates the number of parts of a particular gas relative to one million parts of all gases in the atmosphere. Radiative effectiveness is a term used to describe the ability of a gas to trap radiation energy near the surface of the Earth, and is reported per unit mass.

For the following two questions, come up with an answer on your own. Then, find a partner and discuss this together and write down your answer.

1. Which gas, CO₂ or CH₄, is more abundant in the atmosphere? Which one has had the highest proportional increase since pre-industrial times?
2. If one kilogram of methane trapped 125 units of radiation energy, how many units of radiation energy would one kilogram of CO₂ trap?
3. Based on the data in Table 2 (atmospheric concentration and relative radiative effectiveness), which gas, carbon dioxide or methane, is a larger overall contributor to atmospheric warming? Why?

Part 2
Agriculture is one of the most important anthropogenic (human caused) sources of methane to the atmosphere. Rice is cultivated in wetlands, where there is little oxygen available in the soil. Decomposition of organic matter in these anaerobic environments produces methane instead of carbon dioxide. Methane is also produced in the digestive tracts of ruminant animals (e.g., cows, sheep, etc.) during the digestion process, which is then released to the atmosphere. In fact, one cow can release as much as 500 liters of methane per day (Johnson and Johnson 1995). Animal manure is stored in large holding ponds, where anaerobic bacteria decomposing the manure also release methane to the atmosphere. Most of the methane released to the atmosphere is consumed by a reaction with hydroxyl radicals (OH^-) or is oxidized by soil bacteria to carbon dioxide (these reactions are called "sinks"), but a portion (84 Tg per year) remains in excess in the atmosphere.

Together with a partner, discuss the following:

1. What agriculture activities produce significant amounts of methane?
2. Can you think of other agricultural activities that are not listed on Figure 2a, and therefore do not contribute substantial amounts of methane to the atmosphere?
3. As consumers of food, are there any decisions we could make to reduce the amount of methane emitted to the atmosphere from agriculture?

Write down your answers to these questions and be prepared to share your answers with the rest of the class.