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 by trapping heat in the Earth's atmosphere. Nitrous oxide (N₂O) is considered to be one of the other important greenhouse gases, as human activities have increased its concentration in the atmosphere since pre-industrial time periods.

Examine Table 3a, which provides data from the Intergovernmental Panel on Climate Change (IPCC) 2007 report. Think about what the data mean and make sure you understand all of the terms. Ask your instructor if you are unfamiliar with any of the terms. After interpreting Table 3a, consider the following questions.

• Is there more carbon dioxide or nitrous oxide in the atmosphere?
• Which of the two gases (CO2 or N₂O) has had larger increases in the atmosphere since pre-industrial times?
• In your own words, what do you think relative radiative effectiveness means?.
• Why do you think scientists pay attention to relative radiative effectiveness?
• The concentration of carbon dioxide in the atmosphere is more than 1,000 times higher than nitrous oxide. Why is nitrous oxide considered to be an important greenhouse gas?
• Why might nitrous oxide have a higher relative radiative effectiveness than carbon dioxide?

Part 2

It has been estimated that 50% of human induced nitrous oxide (N₂O) emissions are produced in agricultural soils (IPCC 2001). Nitrogen fertilizers applied to soil increase plant growth and food production, but plants are not the only organisms that use the nitrogen. Soil microorganisms also use nitrogen for growth and energy. Specifically, certain bacteria are involved in the process of nitrification and denitrification, and nitrous oxide is a minor product in both of these reactions.

Figure 3a and 3b show data of N₂O emissions and corn crop yields in a study conducted in corn fields of southwest Michigan. The researchers measured N₂O emissions from soil, but also measured corn crop yields.

Interpret Figure 3a and 3b for a moment on your own. Ask your instructor to describe anything that you do not understand. After examining the figure, consider the following questions.

• Using Figure 3a, do corn yields increase linearly with increasing nitrogen fertilizer rates?
• Using Figure 3b, what happens, in terms of N₂O emissions when a farmer applies more fertilizer than needed for maximum crop growth (more than 101 kg in this study)?
• Do you think that 101 kg of nitrogen fertilizer enough to maximize crop growth in all fields or for all crops?
• Why might a farmer apply more than enough nitrogen fertilizer?
• Corn crops are being grown to produce biofuel (ethanol) for fueling vehicles. This practice is intended to reduce greenhouse gas emissions because less fossil fuel is being used to power vehicles. Based on the data in Figure 3, how might the strategy of growing corn for ethanol actually increase the heat trapping potential of the Earth's atmosphere?