Did Early Farmers Alter Climate?

This exercise in intended for use in an undergraduate, introductory geology or environmental science course. The course may have both majors and non-majors. The exercise could also be used in an undergraduate climate science course.

Prior to beginning the exercise, students should have knowledge of the difference between weather and climate. They should also have introductory knowledge of processes that regulate Earth's climate system, including solar energy, the greenhouse effect, variations in Earth's orbit, and various feedback mechanisms. Students should be familiar with global warming and human activities that are intensifying the greenhouse effect. Concepts related to climate proxies and past climate fluctuations are introduced as the exercise proceeds.

The exercise is completed over a 1.5- to 2-week period as the class covers a chapter on climate change (past, present, and future).

Throughout the exercise, students gain an understanding of changes in greenhouse gas concentrations (CO2 and CH4) over different time periods (pre-industrial and post-industrial). They also learn about the early anthropogenic hypothesis, which claims that early agriculture had a substantial impact on greenhouse gases and global climate thousands of years ago (Ruddiman, 2003).

As part of this exercise, students:
1) Develop an appreciation for rates of changes in CO2 and CH4 concentrations over hundreds of years and over thousands of years.
2) Translate changes in CO2 and CH4 concentrations to estimated global temperature change.
3) Assess the relative contributions of CO2 and CH4 to global temperature change.

As part of this exercise, students:
1) Utilize spreadsheets for graphing and calculations.
2) Summarize measurements in professional figures.
3) Calculate rates of changes in greenhouse gas concentrations.
4) Work in groups to collect, summarize, and present measurements and results.

In addition to introductory material on Earth's climate system, background information on climate proxies and the development of records of greenhouse gas concentrations is presented in class. In part 1 of the exercise, students are divided into four groups. The students in each group plot and analyze greenhouse gas concentrations for a single greenhouse gas (CO2 or CH4) for a given time period (pre-industrial or post-industrial). Each student brings two copies of their graph to class for the following class period. Students turn in one copy for evaluation, and they use the second copy in a discussion with the other students who graphed the same data set. First, they compare their graph to the graphs that other people in the group created. Students make notes if there are things that they would like to update or change in their own graph. They are given the opportunity to make any corrections to their graph prior to the next class meeting. Then, as a group, students discuss and answer a set of questions that explore the pattern of change in greenhouse gas concentration over the period of record in their graph. The group turns in one set of responses to the questions at the end of the class period.

After the students complete part 1 of the exercise, background information on the early anthropogenic hypothesis is presented in class. Students are also asked to read two articles on the early anthropogenic hypothesis, published 10 years apart from one another (Mason, 2004; Ruddiman et al., 2014).

In part II of the exercise, new student groups are formed. Each group includes at least one student from the initial four groups, so that there are student experts on each of the greenhouse gases during both pre-industrial and post-industrial times. Before discussing a new set of questions, each person in the group takes a turn and provides a brief summary of their greenhouse gas concentration chart. Students also use a radiative forcings spreadsheet to calculate the estimated global temperature change relative to 1850, resulting from changes in CO2 and CH4 concentrations. The group turns in one set of responses to the questions at the end of the class period.
Student handout for "Did Early Farmers Alter Climate?" assignment (Microsoft Word 2007 (.docx) 553kB Apr29 20)
CH4 data, pre-industrial (Spreadsheet) (Excel 2007 (.xlsx) 23kB Apr29 20)
CH4 data, post-industrial (Spreadsheet) (Excel 2007 (.xlsx) 10kB Apr29 20) 
CO2 data, pre-industrial (Spreadsheet) (Excel 2007 (.xlsx) 11kB Apr29 20) 
CO2 data, post-industrial (Spreadsheet) (Excel 2007 (.xlsx) 16kB Apr29 20)
Radiative Forcings Spreadsheet (Excel 2007 (.xlsx) 16kB Apr29 20)

This assignment does not need to be conducted on three consecutive days. Lectures can be given in intervening class periods to suit the pace of the course.

Pages 1-2 of the student handout are used for the first day of the assignment. Pages 3-4 of the student handout are used for the second day of the assignment. Pages 5-11 of the student handout are used for the third day of the assignment.

The exercise is informally evaluated through discussion and observation in the lab. Work is also formally evaluated. Initial graphs (part 1) are checked by the instructor and handed back during the following class. Group responses to the part 1 and part 2 questions are also graded.

• IPCC (2019) Summary for Policymakers. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems [P.R. Shukla, J. Skea, E. Calvo Buendia, V. Masson-Delmotte, H.- O. Pörtner, D. C. Roberts, P. Zhai, R. Slade, S. Connors, R. van Diemen, M. Ferrat, E. Haughey, S. Luz, S. Neogi, M. Pathak, J. Petzold, J. Portugal Pereira, P. Vyas, E. Huntley, K. Kissick, M. Belkacemi, J. Malley, (eds.)]. In press.
• Mason, B. (2004) The hot hand of history. Nature 427: 582–583. https://doi.org/10.1038/427582a
• Myhre, G., Shindell, D., Bréon, F.-M., Collins, W., Fuglestvedt, J., Huang, J., Koch, D., Lamarque, J.-F., Lee, D., Mendoza, B., Nakajima, T., Robock, A., Stephens, G., Takemura, T., Zhang, H. (2013) Anthropogenic and Natural Radiative Forcing Supplementary Material. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Available from http://www.climatechange2013.org and http://www.ipcc.ch
• Ruddiman, W. (2003) The anthropogenic greenhouse era began thousands of years ago. Climatic Change 61: 261–293.
• Ruddiman, W., Vavrus, S., Kutzbach, J., He, F. (2014) Does pre-industrial warming double the anthropogenic total? The Anthropocene Review. 1 (2): 2053019614529263. 10.1177/2053019614529263