CLEAN > Teaching Climate and Energy Science > Teaching Climate Science > 6. Humans Affect Climate

Teaching Essential Principle 6:
Human activities are impacting the climate system.

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Teaching this principle is supported by five key concepts:

a. The overwhelming consensus of scientific studies on climate indicates that most of the observed increase in global average temperatures since the latter part of the 20th century is very likely due to human activities, primarily from increases in greenhouse gas concentrations resulting from the burning of fossil fuels.

b. Emissions from the widespread burning of fossil fuels since the start of the Industrial Revolution have increased the concentration of greenhouse gases in the atmosphere. Because these gases can remain in the atmosphere for hundreds of years before being removed by natural processes, their warming influence is projected to persist into the next century.

c. Human activities have affected the land, oceans, and atmosphere, and these changes have altered global climate patterns. Burning fossil fuels, releasing chemicals into the atmosphere, reducing the amount of forest cover, and the rapid expansion of farming, development, and industrial activities are releasing carbon dioxide into the atmosphere and changing the balance of the climate system.

d. Growing evidence shows that changes in many physical and biological systems are linked to human caused global warming. Some changes resulting from human activities have decreased the capacity of the environment to support various species and have substantially reduced ecosystem biodiversity and ecological resilience.

e. Scientists and economists predict that there will be both positive and negative impacts from global climate change. If warming exceeds 2 to 3°C (3.6 to 5.4°F) over the next century, the consequences of the negative impacts are likely to be much greater than the consequences of the positive impacts.

What does this principle mean?

These key ideas relate to the causes and effects of human-induced climate change. The potential for human activities to increase the temperature of the Earth through greenhouse gas emissions has been described and calculated for over a century. Volumes of scientific research across multiple scientific disciplines now support this principle, and the 2007 IPCC Forth Assessment Report states, "There is very high confidence that the net effect of human activities since 1750 has been one of warming."

Atmospheric carbon dioxide concentrations, measured as the mole fraction in dry air on Mauna Loa, constitute the longest record of direct measurements of CO2 in the atmosphere. They were started by C. David Keeling of the Scripps Institution of Oceanography in March of 1958 at a facility of the National Oceanic and Atmospheric Administration (Keeling, 1976). NOAA started its own CO2 measurements in May of 1974, and they have run in parallel with those made by Scripps since then (Thoning, 1989). The black curve represents the seasonally corrected data. See the up to date data . Click to enlarge image.
The issue of attribution - showing definitely that human activities are causing global climate change to occur - is one of the most active areas of climate research. There is substantial evidence that human activities, especially burning fossil fuels, are leading to increased levels of carbon dioxide and other greenhouse gases in the atmosphere, which in turn amplify the natural greenhouse effect, causing the temperature of the Earth's atmosphere, ocean and land surface to increase. That greenhouse gases do "trap" infrared heat is well established through laboratory experiments going back to the mid 1850s when Sir John Tyndall first measured the effect.

The well-documented trend of increasing of CO2 in the atmosphere is related to exponential increases in human population, massive land cover changes and the burning of fossil fuels. The "smoking gun" that shows clearly that human activities are responsible for recent increases in carbon dioxide in the atmosphere is provided by carbon isotopes (carbon atoms of different atomic weight). These isotopes allow scientists to "fingerprint" the source of the carbon dioxide molecules, which reveal that the increased CO2 in the atmosphere reflects the addition of CO2 from fossil fuel burning. (see references)

Smokestacks at a Power Plant
Why is it important?

In this principle we examine how, due to basic physics of heat trapping gases and exponential rise in population and energy consumption, humans have become a force of nature. Clearly, this is a complex topic with enormous political, socio-economic and emotional dimensions, but the scientific results show clearly that:

Carbon emissions have risen from about 2.5 gigatons per year in the late 1950s to 9 gigatons per year today. This graph shows a breakdown of carbon emissions by their source. Source: Data from Oak Ridge National Laboratory. Click image to enlarge.

What makes this principle challenging to teach?

Quite simply, this principle is challenging to teach because some sectors of the public continue to debate whether these ideas can be true, despite the well-established science. There are several possible reasons why students may resist the conclusion that humans are altering the climate. This concept may be uncomfortable to students due to feelings of guilt, political resistance or genuine lack of scientific understanding. Furthermore, projections of the effects of climate change on our society can frighten, overwhelm, or discourage students. This can result in denial or resistance to learning. Thus educators are encouraged to introduce this topic with generous scaffolding that establishes the foundations of the process of science, the underlying principles of climate science, and a reliance on the robust scientific research that supports this conclusion. Several strategies are presented on this page about Teaching Controversial Environmental Issues which emphasizes students' affective domain.

Integrating Solutions:

Climate and energy-related science topics are often complicated, technically challenging, non-intuitive and potentially emotionally overwhelming and politically sensitive. When individuals begin to grasp the nature and scale of the problems associated with climate and energy, they often want to know "what can I do?" Without realistic options and opportunities to address the challenges, learners of all ages can feel discouraged and turned-off by the science. What many educators have begun to do, as a way to deal with the scientific, technical and emotional difficulties of the subject matter, is weave solutions into the discussion every step of the way.

AAAS Benchmarks for Science Literacy

The AAAS Project 2061 Benchmarks for Science Literacy illustrate connections between concepts as well as how concepts build upon one another across grade levels.

Many of the CLEAN activities that teach Principle 6 fall within the Earth or the processes that shape the earth benchmarks.

Explore the map of climate and energy concepts for this principle:

Processes that shape the earth (middle school)
The Earth (high school)

Learn more about CLEAN maps of climate and energy concepts

How can I use this principle in my teaching?

Middle school students will be familiar with climate change/global warming gathered from the media, family or at school. This can be an opportunity to develop their understanding of how human activities connect to climate change, particularly the increase in CO2 in the atmosphere. See the activity Automotive Emissions and the Greenhouse Effect.

High school educators can help students understand the many connections between human activities and the climate system. This can be done from a historical perspective, or can employ an Earth-systems science approach. See Mauna Loa CO2 Collection Data.

The introductory undergraduate level students can be challenged to apply their understanding of the science in a social context. The activity Global Climate Change: The Effects of Global Warming examines trends in carbon dioxide emissions and considers the human influences on atmospheric carbon dioxide concentrations.

Upper-level college students can examine datasets and employ models that illustrate the anthropogenic contributions to climate change. By having students work directly with the data and models, students can discover their own conclusions about the linkages. For an example, see Using a mass balance model to understand carbon dioxide and its connection to global warming.

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Figure 2.4 from the IPCC 4th Assessment Report, showing the different types of processes that affect earth's climate, also called "forcings." Click image to enlarge.

Detailed image caption from IPCC: Global average radiative forcing (RF) in 2005 (best estimates and 5 to 95% uncertainty ranges) with respect to 1750 for CO2, CH4, N2O and other important agents and mechanisms, together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU). Aerosols from explosive volcanic eruptions contribute an additional episodic cooling term for a few years following an eruption. The range for linear contrails does not include other possible effects of aviation on cloudiness.
This figure is from the drivers of climate change section of the report.


From the 2007 IPCC Forth Assessment Report summary for policymakers: Causes of Climate Change, or for greater detail see the more complete discussion in the section about drivers of climate change

How do we know that recent CO2 increases are due to human activities? - a scientific summary from

The human fingerprint in coral - This page from the Skeptical Science website provides clear answers to common questions and misunderstandings about climate change.

Solar Variability & Global Climate Change - This summary from the Standford Solar Center describes the relationship between sunspots, solar irradiance and climate change

New statistical analysis confirms human role in climate change - A summary of physics research that uses a simple, statistical approach to understand causes of climate change.

Causes of Climate Change - This NASA web page describes the greenhouse effect, the role of human activity and the evidence that changes in solar irradiance are not related to recent temperature increases.

Global Warming's Six Americas - This report from a large national survey of American adults identifies six unique audiences within the American public that each responds to the issue in their own distinct way. This is a great way to learn about the possible audiences among your student population.

Examining the Scientific Consensus on Climate Change, P. Doran, M. Zimmerman. EOS, Transactions American Geophysical Union, 2009, vol. 90, no. 3, p. 22, 200. This article compares the consensus views of scientists and the general public on climate change.

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