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Human Energy Systems | Goals

General Unit Information

Human Energy Systems is the culminating unit in the Carbon TIME sequence, focusing on global-scale phenomena: climate change and global carbon cycling. We recommend that teachers complete the Systems & Scale, Plants, and Ecosystems units before the Human Energy Systems unit if possible. The foundational knowledge introduced in these units helps prepare students to engage in conversations and activities that require a basic understanding of photosynthesis, cellular respiration, and combustion of fossil fuels (on a cellular or atomic-molecular scale) and apply these concepts to carbon cycling and energy flow (on a global scale). It is through examining the pools and fluxes of carbon at a global scale that students will be able to make connections between energy use, combustion of fossil fuels, carbon emissions, and climate change.

The Instructional Model now reflects the two phases of the unit. The first phase focuses on helping students to understand, analyze, and explain multiple phenomena associated with climate change (What is happening to the planet?). The second phase focuses on global carbon cycling. In each phase students practice the roles of questioner, investigator, and explainer.

Phase 1: What is happening to the planet? (climate change)

In Lessons 1-3 students question, investigate, and explain four phenomena associated with climate change: Arctic sea ice, global sea levels, global average temperatures, and atmospheric CO2 concentrations.

Lesson 1: After taking the unit pretest, students begin by expressing their ideas and questions around a single phenomenon: Arctic sea ice. They begin with ideas and questions about a single pair of images, comparing the extent of Arctic sea ice in 1979 and 2016. They then investigate data on Arctic sea ice over multiple years, learning to make graphs that show two patterns: (a) the extent of ice varies unpredictably from one year to the next, and (b) there is a long-term trend toward reduced ice cover.

Observations, Patterns, and Models in the Human Energy Systems Unit

Lesson 2: Students investigate multiple representations of data about three other phenomena, comparing the representations to look for patterns in the data. They end the lesson with four clear long-term trends:

  • The extent of Arctic sea ice is decreasing
  • Sea levels are rising
  • Global average temperatures are rising
  • Global concentrations of CO2 are rising

Observations, Patterns, and Models in the Human Energy Systems Unit

Lesson 3: Students learn about the Greenhouse effect and use it to explain the connections among the long-term trends: Increasing CO2 levels are causing increases in global temperatures; the increasing temperatures are causing sea level to rise and ice to melt. Thus atmospheric CO2 is the driver—the factor that causes change in the other variables.

Observations, Patterns, and Models in the Human Energy Systems Unit

Phase 2: What causes changes in CO2? (global carbon cycling)

In the second half of the unit students investigate and explain “what drives the driver”—what is causing changes in atmospheric CO2 levels.

Lesson 4: Students begin by sharing questions and hypotheses and make predictions about how reducing fossil fuel use will affect atmospheric CO2 using the Big Ideas Probe. They are introduced (or re-introduced if they studied Ecosystems) to the Large-scale Four Questions tool. (see the Four Questions Large Scale Handout). These Four Questions are referred to throughout the unit to scaffold students in their interpretation of energy use and carbon-transforming processes in the context of human economic activities. In particular, students should learn to answer the Carbon Pools Question, the Carbon Cycling Question, the Energy Flow Question, and the Stability and Change Question in three important contexts:

  1. At the macroscopic scale, they relate our economic activities and lifestyle choices to carbon-transforming processes, especially combustion of fossil fuels. Students should understand both activities that directly use fossil fuels (such as driving a car) and activities that indirectly use fossil fuels (such as using electrical appliances or buying products that require fossil fuels for manufacture and transportation).
  2. Relating local systems, actions, and choices to global effects and outcomes, particularly increasing concentrations of carbon dioxide in the atmosphere.
  3. Relating changes in global carbon pools (the atmosphere, biomass, soil organic carbon, and organic carbon in fossil fuels) to the balance of fluxes of carbon between these pools.

Students use three different kinds of pool-and-flux models to explain both the annual cycle and the long-term trend in CO2 concentrations:

  • The Tiny World Game (Activity 4.3) is a hands-on activity in which students move counters to investigate the effect of different balances among photosynthesis, cellular respiration, and combustion fluxes on atmospheric, environmental organic carbon, and fossil fuel pools.
  • The Global Carbon Model (Activity 4.4) is an online model that students can manipulate to predict how different changes in carbon fluxes will affect carbon pools.
  • The Global Carbon Cycling Diagram (Optional Activity 4.5) adds the oceans as another carbon pool. Students make predictions that include carbon fluxes into and out of the oceans using the diagram.

Lesson 5: Students learn from Lesson 4 that combustion of fossil fuels is the unbalanced flux that drives the continuing increase in atmospheric CO2 concentrations (and therefore climate change). In Lesson 5 they explore how human activities, including their own lifestyles, depend on combustion of fossil fuels—often in hidden ways. Students investigate how lifestyles associated with different countries (United States, France, China, and Ethiopia) lead to vastly different rates of fossil fuel combustion. They also examine how their own everyday activities (e.g., buying a pizza, washing dishes) use energy from fossil fuels and changes that could reduce carbon emissions.

Lesson 6: The unit concludes with a series of activities in which students make projections of how different scenarios will affect global temperatures as atmospheric CO2 concentrations. They use a computer to make projections, then discuss different scenarios for Earth’s future, and how those scenarios will affect their lives.

A note on media literacy

This unit makes extensive use of data and models from authoritative sources. Its contents are not scientifically controversial, and are consistent with the Next Generation Science Standards. The data and models in this unit are complex, but critically important. The unit has many scaffolds, including the Questions, Connections, Questions Student Reading Strategy, to scaffold students’ understanding.

Some students might respond to the material presented in this unit by offering conflicting claims they have heard about climate change from their families, friends, or the media. Footnotes are included throughout the Teacher’s Guide to help you respond to these claims using with the evidence the scientific community looks to interpret these conflicting claims. Although scientists view climate change as a matter of scientific evidence and not one of morals and values, the students may feel that their core values and viewpoints are being threatened, which could in turn cause them to disengage. The footnotes included in this unit are intended to provide additional perspectives you might use to help your students interpret the claims they are making in light of the available evidence for anthropogenic climate change.

While we want to encourage students to ask questions and engage in dialogue about the conflicting claims about climate change, we also want to encourage these conversations to be constrained by accurate scientific evidence. Look for footnotes throughout the Teacher’s Guide-- these are designed to help you navigate these conversations if they arise.

Unit Goals

The tables below show goals for this unit in two forms. Table 1 shows unit learning objectives aligned with the Three Questions. Table 1 also contrasts the goal performance with performances of students at lower learning progression levels.

This table is followed by a list of Next Generation Science Standards (NGSS) addressed by this unit.

Table 1: Unit Learning Objectives

Human Energy Systems Unit

Type of Objective

and NGSS Practice

Learning Objectives

Challenges for Level 2 Students

Challenges for Level 3 Students

Interpreting representations of large-scale data sets

Explain how data are sampled and represented in different representations of large-scale data sets (e.g., graphs, maps, videos).

Use large-scale data sets related to climate change (sea level rise, global temperature, atmospheric CO2 long-term trend, and atmospheric CO2 short-term variability) to make predictions about the future.

Distinguish between short-term variability and long-term trends in large-scale data sets.

Distinguish between local signals and global trends in large-scale data sets.

Level 2 students will focus on surface features of representations, noticing patterns and trends without connecting them to changes in Earth systems.

Level 3 students will provide interpretations of representations of large-scale data sets, but will have difficulty relating different representations of the same data (e.g., relating data from a single location to global patterns, distinguishing short-term variation from long-term trends)

Carbon Pools Question

Locate organic and inorganic carbon pools near the Earth’s surface (atmosphere, biomass, soil, fossil fuels, and ocean).

Describe pools as changing in size over time.

Level 2 students will think of carbon as a kind of material rather than as an atom in many carbon-containing molecules.

Level 3 students may not think of the same carbon atoms in the atmosphere, biomass, soil, and fossil fuels.


Carbon Movement Question

Explain changes in atmospheric CO2in terms of fluxes associated with carbon-transforming processes: combustion, photosynthesis, cellular respiration.

Describe carbon cycling within Earth and Human systems.

Identify carbon fluxes associated with human economic activities.

Level 2 students will explain carbon-transforming processes as series of causally connected events (humans burn coal; plants take in CO2; oceans absorb CO2, etc.)

Level 3 students will recognize fluxes as involving movements of matter, but not that fluxes BOTH make one pool larger AND make another pool smaller.


Energy Question

Identify energy transformations involved in carbon fluxes.

Trace energy associated with human lifestyles to its sources, particularly combustion of fossil fuels.

Describe energy as flowing through Earth systems, from sunlight to chemical energy to heat that is radiated into space.

Level 2 students will describe energy as a cause of events rather than a conserved entity that can be traced through systems.

Level 3 students are likely to be partially aware of connections between human activities, energy use, and combustion of fossil fuels.

Level 3 students may also have difficulty tracing energy on its complete pathway from sunlight back into space.


Citizenship and Decision Making



Explain the consequences of lifestyle and energy system choices for changes in atmospheric CO2 concentration.


Level 2 students evaluate strategies for reducing energy use or carbon emissions as generically “good” or “bad” for the environment.

Level 3 students identify specific processes as affecting CO2 levels in the atmosphere, but not in terms of movement among carbon pools.