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Is Warming Natural or Anthropogenic?

By Cindy Shellito, Professor of Meteorology
University of Northern Colorado, Department of Earth and Atmospheric Sciences
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In this activity, students examine climate model output for the past, present, and future. They compare changes in temperature and precipitation patterns between experiments, and consider what factors contribute to those changes. After the model analysis, students watch a TED talk by Dr. Jon Foley about the effects of deforestation on climate. Finally, students participate in small-group and full-class discussions about the effects of land surface changes on climate, and the role of models in helping us understand climate change.

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Learning Goals

The primary aims of the activity are (1) to introduce students to how we use climate models to determine human impacts on climate over the 20th century, and (2) to have students consider the impacts of anthropogenic land surface change and feedbacks of this on climate.

Within this context, students will learn the following concepts:
  • Models can show the impacts of increasing greenhouse gases on the global climate
  • Impacts of warming are not uniformly distributed across the globe
  • Global temperature is sensitive to an increase in greenhouse gases
  • Temperature, ice distribution, and precipitation have changed since the Pre-Industrial Era, and these changes are forecasted to continue through the 21st century
  • Deforestation and changes in land surface cover are playing a significant role in climate change.
Students will also have a chance to practice:
  • Analysis and synthesis of model results
  • Application of model results to a growing understanding of how the climate system works
  • Consideration of factors not included in the climate model
  • Consideration of how land-management practices and human needs are inextricably linked to climate change - how humans have already had an impact and how they will continue to have an impact
The final discussion associated with this activity requires students to consider how we, as a civilization, can adapt or respond to the changes that are already underway and how we can build resilience to present and future risks of climate change.

Context for Use

This activity is designed for an upper division science course focused on environmental science or climate change. It can be used as a lab activity or as a discussion in a lecture class. It was tested in a Paleoclimatology course with 16 students at the University of Northern Colorado. All students were juniors or seniors majoring in Geology, Meteorology, Environmental Science or Secondary Education-Earth Sciences. All students had taken an introductory science course with a lab (e.g., Introductory Geology or Meteorology). The course met 3 days a week for 50 minutes at a time, and this activity took 3 class sessions. The activity was situated at the end of the course, after we had discussed the physical factors that affect global climate and after we had considered natural factors that affect climate change throughout Earth history. However, this same activity could be implemented in a course focused on modern climate change near the beginning of the course, as long as students understand the following concepts:
  • General circulation of the atmosphere (Hadley and Ferrel cells) and its role in creating latitudinal variations on climate
  • The role of albedo on climate
  • The role and importance of greenhouse gases in the climate system
  • The definition of a 'feedback' and how this can be applied to processes in the climate system
  • How a global climate model works (in a very basic sense), and how we use them to test climate sensitivity

Description and Teaching Materials

This lesson is best divided into three parts.

Part 1 (one 50-minute class period): In this part of the lesson, students examine climate model output available online and compare pre-industrial climate with climate of the late 20th century. (Students will be working with this handout: Student Handout for Comparing Past and Present Climate Model Output (Microsoft Word 2007 (.docx) 92kB Sep13 16) ) The first page of the handout prompts students to consider the type of model that created the results they are looking at (a 3-dimensional global climate model), and a bit about how it works. Students should have some understanding of the ways in which global climate models are used to test the sensitivity of climate to changes in forcing. They are also prompted to consider questions they would ask about how climate changed through the 20th century, and how they might use the model output to answer those questions. (This could be accomplished through a brief class discussion with the introduction to the activity).

In groups of 2-3, students should work to complete the 2nd and 3rd pages of the activity, examining climate online, and considering how much CO2 has changed in the atmosphere over the last century.

Finally, the last page of the activity instructs students to complete a short homework assignment that requires them to respond to a short reading about deforestation and watch a TED talk by Jonathan Foley. The homework must be completed before the third part of the lesson.

Part 2 (one 50-minute class period): In the second part of this lesson, students examine future climate predictions based on IPCC scenarios. (Students will be working with the handout: Student Handout for Future Climate Model Analysis (Microsoft Word 2007 (.docx) 106kB Sep13 16)). In this part of the lesson, there will be an opportunity to debrief as a class regarding the first activity in Part 1. It helps to start the class with a chart on the board where students can add some of their observations from examining differences between pre-industrial and present-day climate. As a class, discuss the biggest differences, then ask students to consider where they might expect to see the biggest changes in climate in the next 100 years. This question leads into the examination of future climate using the same website they used in Part 1.

Part 3 (~25 minutes): In the third part of this lesson, students participate in a small group discussion and respond to the following prompts: What are the greatest climate impacts in the future scenario you looked at in class on Wednesday? What is your group consensus on the greatest impact to human civilization if the predictions of this computer simulation come to pass? What do you think is the greatest challenge we face related to climate change (this can include the challenges discussed in the TED talk by Dr. Foley)? What might be one way of mitigating or adapting to changes that are coming in the next few decades? (Prompts available in the file: Discussion Prompts for Future Climate (Microsoft Word 2007 (.docx) 52kB Sep13 16))

After the small group discussion, it's helpful to have a large class discussion about each of the prompts, while listing on the board some of their responses to the prompts.

Teaching Notes and Tips

There are a few things that will help this activity run a bit more smoothly:
1) If students have not used the NCAR website prior to their analysis of model results in Part 1, it's helpful to spend 5-10 minutes providing them a 'tour' of the website and the types of results they can look at. They have the option of looking at MANY different variables. Have them focus on global maps (SETS 5 & 6) and focus on the annual average (ANN) of temperature and precipitation (and perhaps ice).
2) After Part 1 of the activity, during a class debriefing, it's helpful to remind students of the physical effects of increased greenhouse gases on climate, and how those play out in these climate simulations (specifically, it's helpful to look at changes in albedo associated with changes in ice cover, and discuss what effect that has on temperature).
3) There may be some emotional strong reactions to Dr. Jon Foley's TED talk and ideas students have about human impact on climate. Depending on the classroom environment, it might be helpful to lay out some ground rules for discussion (be willing to hear differences of opinion, choose your words carefully, be respectful, etc.)


PRE-ASSESSMENT: Prior to introducing the activity, a pre-assessment question was distributed to students as part of an in-class quiz. The assessment asked students: "How would you go about determining if warming in the past century is natural or anthropogenic?"
FINAL ASSESSMENT: Students were given three questions on the final exam to assess (1) their skill in analyzing model results, (2) understanding of how models are used to pinpoint human contribution to climate change, (3) understanding of the role of land surface change in climate. Assessment questions are in the file: Final Exam Assessment Questions (Microsoft Word 736kB Sep13 16)

References and Resources

1) Parts 1 and 2 of the lesson require access output from experiments with the NCAR Community Earth System Model.
Part 2 uses output from future modeling experiments.

2) Ice core data from the Carbon Dioxide Information Analysis Center.

3) Current CO2 level in the atmosphere at

4) Carbon Brief: Deforestation Affects Climate Around the World, Study Finds, by Robert McSweeney. This article provides a brief overview of a study. Depending on student background and the degree to which you wish to discuss the effects of deforestation on climate, you may wish to have students read the entire article: Lawrence, D. and Vandecar, K. (2014) Effects of tropical deforestation on climate and agriculture, Nature Climate Change,

6) After Part 1 of the activity, students are required to watch a TED talk by Dr. Jonathan Foley.
This program description is part of a growing collection of models of ways to bring learning about the Earth to a diverse range of disciplines, institutions, and networks, as well as provide the documentation and resources necessary to help other groups implement similar programs..
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