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Human Energy Systems | Activity 4.5

Activity 4.5: The Upward Trend (30 min)

Students use what they have learned in the Unit to answer the final question about the Keeling Curve: Why are concentrations of carbon dioxide increasing in the atmosphere?

Materials You Provide

Resources Provided


Prepare one copy of 4.5 The Upward Trend Worksheet for each student. Prepare a computer with Internet and projector for the Pumphandle Video. This video is downloadable, though it is a large file. You may choose to download the video before class in order to avoid Internet issues. Retrieve the students’ completed 2.1 Finding Patterns Tool for Earth Systems from Lesson 2.


1. Recall the Keeling Curve and identify the seasonal cycle.

Pass out a copy of 4.5 The Upward Trend Worksheet to each student and have students look at the image of the Keeling Curve.

  • Recall the seasonal cycle, which is caused by the seasonal rates of photosynthesis and cellular respiration.
  • Identify the upward trend in the Keeling Curve: the (red) line that moves continuously upward over time.
  • The purpose of this activity is to explain why this line is going up (why carbon dioxide concentration is increasing in the atmosphere).


Use 4.5 Assessing the Upward Trend Worksheet to monitor students’ ideas about the upward trend in the Keeling Curve. If they are still struggling to understand the cause of the upward trend (increasing uses of fossil fuels in the atmosphere), you may want to discuss the worksheet responses as a class.


Watch the video a few times to allow students to ask questions and to check for comprehension of the many different components of the video.


Have students watch the video one time through without pausing or asking questions. Then, afterwards, have students explain what they were seeing.

Extending the Learning

Have students show the video to a friend or family member, explain what is happening in the video, and report to the class how the conversation went.


This video is a nice opportunity to point out that even though there are short-term variations in the temperature and CO2 levels, that the overall trend is still increasing. Students may ask “If global warming is happening why was it so cold this winter?” Even as the global temperatures continue to increase, we will still see unusually cold winters and even summers. These short term cold periods (e.g., one season or month) are due to local weather, short-term changes in the movement of polar winds, and ocean circulations, and do not reflect the overall warming trend. However, it is predicted that climate change might make some of these local, extreme weather events more sever over a long time scale.

During this Activity (or at other places in the unit) some students may suggest that we shouldn’t be alarmed about the current levels of CO2 in the atmosphere because they have been this high before in the past, but that is not shown in the video. Point out that the concern is because CO2 levels are higher than they have every been in the past 800,000 years when humans evolved to live on the Earth, and the concern is that humans will have a big challenge in adapting to the changes that come along with these increases. You might also want to point out that it is true that CO2 levels have been higher than now (400 ppmv) in the Earth’s history (they reached about 1000 ppmv about 50 million years ago), but that was millions and millions of years ago, before people lived on the Earth. At that time (when CO2 levels were very high), the temperatures were also higher (about 10° C warmer than today) and sea level was higher as well (about 60 meters higher than today). If we went back to that climate now, much more of the land on which people currently live would be underwater, and it would be very hot. This is why scientists are concerned.

Some students may suggest that such a small amount of CO2 couldn’t possibly impact such a large atmosphere. After all, 400 parts per million isn’t a large percentage of the atmosphere at all! Point out that just like a small amount of poison can make a person very sick, so can small amounts of greenhouse gases cause the temperature to warm. And just a very small rise in global temperatures can have a big impact on the global climate. Remember: the temperature on the planet during the last ice age was only about 5 degrees colder than it is now! This means that small increases in greenhouse gases can have big impacts on temperature, which have big impacts on our climate, both for the environment and also people.