Heat, The Ocean, and Climate Change

Text: Q = mcDT  The Ocean and Climate Change

For the past few years when I’ve been covering introductory concepts in thermodynamics, I’ve made a connection to climate change. My students and I calculate the energy that has been gained by Earth’s oceans as heat, using the following equation that is familiar to students of introductory and general chemistry:

Q = mcT                   Equation 1

where Q is the energy gained as heat, m is mass, c is the specific heat of water (taken to be 4.2 J g-1 oC-1), and T is the change in temperature.

After students become familiar with the use of this equation, we apply it to the warming that has been observed in the world’s oceans. First, it is noted that 93% of the excess energy trapped on Earth as a result of the warming effect from greenhouse gas emissions is stored in the oceans.1-3 Next, students are informed that measurements at the top 2000 m of ocean water from 1960 to 2015 have shown an increase in water temperature by 0.13oC over this time period.4 Given that the top 2000 m of the Earth’s oceans have a mass of 7.38 x 1023 g,5 we can calculate the energy gained by the oceans in this 55-year time span:

Q = (7.38 x 1023 g)( 4.2 J g-1 oC-1)(0.13oC) = 4.0 x 1023 J

After calculating this remarkably large amount of energy, it is instructive to provide some context. To do this, students are asked to calculate how many Hiroshima sized atomic bombs (63 x 1012 J)6 are equivalent to the amount of energy:

This is truly a tremendous amount of energy. At this point I try to impress upon students the fact that small increases in temperature require enormous amounts of energy if the object being warmed is very massive. In general, I think it is a good idea for people to be cognizant of this relationship, especially when thinking about climate change. This is because the public often views the reported increases in atmospheric temperatures (~1oC since the Industrial Revolution)2 to be rather insignificant. People should be aware that such “small” increases in temperature tend to conceal the fact that Earth’s various systems (lithosphere, atmosphere, hydrosphere) have needed to gain enormous amounts of energy to drive the temperature change. I also use these calculations to drive home to students the difference between heat energy and temperature (often a point of confusion for students). Obviously, a small increase in temperature (+0.13oC) in a very massive object (the top 2000 m of the Earth’s oceans) requires the storage of a staggering amount of energy.

Next, I have students calculate the average of how many atomic bombs worth of energy must have been taken in by the oceans per second over this time period:

These calculations allow for further discussion such as why hurricanes might be increasing in intensity. Furthermore, students can gain insight into why it will take some time for recorded temperatures to drop even if we stopped emitting greenhouse gases in the atmosphere immediately.

If you try these calculations with your students in your class, please let me know how it went for you. Also, be sure to let me know of any other topics of discussion that these calculations may have sparked in your classroom.

References:

1. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

2. Dressler, A. Introduction to Modern Climate Change, 2nd ed.; Cambridge University Press, Cambridge, 2016.

3. The Warming Papers: The Scientific Foundation for the Climate Change Forecast; Archer, D.; Pierrehumbert, R.; Eds.;  John Wiley & Sons, Hoboken, NJ, 2010, Chapters 1–6.

4. Cheng, L.; Trenberth, K. E.; Fasullo, J. T.; Boyer, T.; Abraham, J. P.; Zhu, J. Improved estimates of ocean heat content from 1960 to 2015. Sci. Adv. 2017.

5. In Charette, M. A.; Smith, W. H. F. The Volume of the Earth’s Oceans, Oceanography, 2010, 23, 112-114, the area of the Earth’s oceans was measured to be 362 x 106 km2. Using this measured area and volume = area x depth, a volume of 7.23 x 1023 cm3 is calculated for a depth of 2 km. Assuming ocean water has a density of 1.02 g cm-3, a mass of 7.38 x 1023 g is calculated for the top 2000 m of ocean water.

6. Pearson, E. F. Hurricane Ike versus an Atomic Bomb. J. Chem. Educ. 2013, 90, 90-92.

NGSS

Earth’s Systems, help students formulate an answer to the question: “How and why is Earth constantly changing?” The ESS2 Disciplinary Core Ideafrom the NRC Framework is broken down into five sub-ideas: Earth materials and systems, plate tectonics and large-scale system interactions, the roles of water in Earth’s surface processes, weather and climate, and biogeology. For the purpose of the NGSS, biogeology has been addressed within the life science standards. Students develop models and explanations for the ways that feedbacks between different Earth systems control the appearance of Earth’ssurface. Central to this is the tension between internal systems, which are largely responsiblefor creating land at Earth’s surface, and the sun-driven surface systems that tear down the land through weathering and erosion. Students begin to examine the ways that human activities cause feedbacks that create changes to other systems. Students understand the system interactions that control weather and climate, with a major emphasis on the mechanisms and implications of climate change. Students model the flow of energy between different components of the weather system and how this affects chemical cycles such as the carbon cycle. The crosscutting concepts of cause and effect, energy and matter, structure and function and stability and change are called out as organizing concepts for these disciplinary core ideas. In the ESS2 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and carrying out investigations, analyzing and interpreting data, and engaging in argument; and to use these practices to demonstrate understanding of the core ideas.

More information about all DCI for HS-ESS2 can be found .

Summary:

Earth’s Systems, help students formulate an answer to the question: “How and why is Earth constantly changing?” The ESS2 Disciplinary Core Ideafrom the NRC Framework is broken down into five sub-ideas: Earth materials and systems, plate tectonics and large-scale system interactions, the roles of water in Earth’s surface processes, weather and climate, and biogeology. For the purpose of the NGSS, biogeology has been addressed within the life science standards. Students develop models and explanations for the ways that feedbacks between different Earth systems control the appearance of Earth’ssurface. Central to this is the tension between internal systems, which are largely responsiblefor creating land at Earth’s surface, and the sun-driven surface systems that tear down the land through weathering and erosion. Students begin to examine the ways that human activities cause feedbacks that create changes to other systems. Students understand the system interactions that control weather and climate, with a major emphasis on the mechanisms and implications of climate change. Students model the flow of energy between different components of the weather system and how this affects chemical cycles such as the carbon cycle. The crosscutting concepts of cause and effect, energy and matter, structure and function and stability and change are called out as organizing concepts for these disciplinary core ideas. In the ESS2 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and carrying out investigations, analyzing and interpreting data, and engaging in argument; and to use these practices to demonstrate understanding of the core ideas.

Assessment Boundary:
Clarification:

Students who demonstrate understanding can use a model to describe how variations in the flow of energy into and out of Earth’s systems result in changes in climate.

More information about all DCI for HS-ESS2 can be found  and further resources at .

Summary:

Students who demonstrate understanding can use a model to describe how variations in the flow of energy into and out of Earth’s systems result in changes in climate.

Assessment Boundary:

Assessment of the results of changes in climate is limited to changes in surface temperatures, precipitation patterns, glacial ice volumes, sea levels, and biosphere distribution.

Clarification:

Examples of the causes of climate change differ by timescale, over 1-10 years: large volcanic eruption, ocean circulation; 10-100s of years: changes in human activity, ocean circulation, solar output; 10-100s of thousands of years: changes to Earth's orbit and the orientation of its axis; and 10-100s of millions of years: long-term changes in atmospheric composition.

Students who demonstrate understanding can plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

More information about all DCI for HS-ESS2 can be found and further resources at.

Summary:

Students who demonstrate understanding can plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

Assessment Boundary:
Clarification:

Emphasis is on mechanical and chemical investigations with water and a variety of solid materials to provide the evidence for connections between the hydrologic cycle and system interactions commonly known as the rock cycle. Examples of mechanical investigations include stream transportation and deposition using a stream table, erosion using variations in soil moisture content, or frost wedging by the expansion of water as it freezes. Examples of chemical investigations include chemical weathering and recrystallization (by testing the solubility of different materials) or melt generation (by examining how water lowers the melting temperature of most solids).

Students who demonstrate understanding can develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.

*More information about all DCI for HS-PS1 can be found at  and further resources at .

Summary:

Students who demonstrate understanding can develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.

Assessment Boundary:

Assessment does not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products.

Clarification:

Emphasis is on the idea that a chemical reaction is a system that affects the energy change. Examples of models could include molecular-level drawings and diagrams of reactions, graphs showing the relative energies of reactants and products, and representations showing energy is conserved.

Energy help students formulate an answer to the question, “How is energy transferred and conserved?” The Core Idea expressed in the Framework for PS3 is broken down into four sub-core ideas: Definitions of Energy, Conservation of Energy and Energy Transfer, the Relationship between Energy and Forces, and Energy in Chemical Process and Everyday Life. Energy is understood as quantitative property of a system that depends on the motion and interactions of matter and radiation within that system, and the total change of energy in any system is always equal to the total energy transferred into or out of the system. Students develop an understanding that energy at both the macroscopic and the atomic scale can be accounted for as either motions of particles or energy associated with the configuration (relative positions) of particles. In some cases, the energy associated with the configuration of particles can be thought of as stored in fields. Students also demonstrate their understanding of engineering principles when they design, build, and refine devices associated with the conversion of energy. The crosscutting concepts of cause and effect; systems and system models; energy and matter; and the influence of science, engineering, and technology on society and the natural world are further developed in the performance expectations associated with PS3. In these performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and carry out investigations, using computational thinking and designing solutions; and to use these practices to demonstrate understanding of the core ideas.*

*More information about all DCI for HS-PS3 can be found at 

Summary:

Energy help students formulate an answer to the question, “How is energy transferred and conserved?” The Core Idea expressed in the Framework for PS3 is broken down into four sub-core ideas: Definitions of Energy, Conservation of Energy and Energy Transfer, the Relationship between Energy and Forces, and Energy in Chemical Process and Everyday Life. Energy is understood as quantitative property of a system that depends on the motion and interactions of matter and radiation within that system, and the total change of energy in any system is always equal to the total energy transferred into or out of the system. Students develop an understanding that energy at both the macroscopic and the atomic scale can be accounted for as either motions of particles or energy associated with the configuration (relative positions) of particles. In some cases, the energy associated with the configuration of particles can be thought of as stored in fields. Students also demonstrate their understanding of engineering principles when they design, build, and refine devices associated with the conversion of energy. The crosscutting concepts of cause and effect; systems and system models; energy and matter; and the influence of science, engineering, and technology on society and the natural world are further developed in the performance expectations associated with PS3. In these performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and carry out investigations, using computational thinking and designing solutions; and to use these practices to demonstrate understanding of the core ideas

Assessment Boundary:
Clarification:

Analyze a Major Global Challenge is a performance expectation related to Engineering Design HS-ETS1. 

 

Summary:

Analyze a major global challenge to specify qualitative and quantitative criteria and constraints for solutions that account for societal needs and wants.

Assessment Boundary:
Clarification:

Students analyze a major global problem. In their analysis, students: Describe the challenge with a rationale for why it is a major global challenge; Describe, qualitatively and quantitatively, the extent and depth of the problem and its major consequences to society and/or the natural world on both global and local scales if it remains unsolved; and Document background research on the problem from two or more sources, including research journals. Defining the process or system boundaries, and the components of the process or system: In their analysis, students identify the physical system in which the problem is embedded, including the major elements and relationships in the system and boundaries so as to clarify what is and is not part of the problem: and In their analysis, students describe* societal needs and wants that are relative to the problem. Defining the criteria and constraints: Students specify qualitative and quantitative criteria and constraints for acceptable solutions to the problem.