15.0 Module Overview and Objectives

Module Objectives 

Use these to help guide your studying and note taking

By the end of this module you should be able to:

1. Recall discovery and cause of the ozone hole. 

2. Recall the history of Chlorofluorocarbons (CFCs). 

3. Review the natural greenhouse effect with the enhanced greenhouse effect. 

4. List the naturally occurring greenhouse gases in Earth’s atmosphere. 

5. Define global warming potential. 

6. Identify  how global warming potential, concentration, and atmospheric lifetime all contribute to the impacts of a greenhouse gas. 

7. Use the following terms Milankovitch cycles, plate tectonics, aerosols to identify the impact on natural climate variability. 

8. Identify the Keeling curve and its significance. 

9. Identify indicators/consequences of climate change. 

10. Idenitfy the basic components and benefits and limitations of climate models. 

11. Define: Weather, Climate, Radiative forcing. 

Module Assignments

[Quiz] Quiz 7

• Answer the questions based on the material in Module 15: Climate. 

• Multiple Choice, True or False 

15.1  Human Impact on Stratospheric Ozone

The Ozone Hole 

Stratospheric ozone is a topic that spans between our last unit on air pollution and this unit on climate.  As an introduction to stratospheric ozone and the ozone hole, watch the video below.  Be sure to reflect on the questions listed beneath the video.

Link:  The Antarctic Ozone Hole -- From Discovery to Recovery, a Scientific Journey

(UN Environment Programme, 2011) 

Questions To Reflect On:

1.  What is the chemical formula for ozone?

2.  What layer of the atmosphere is the ozone layer in?

3.  How does the ozone layer benefit life on Earth?  What would be some of the human consequences of large amounts of ozone depletion?

4. Why was the “ozone hole” only discovered after 30 years of monitoring ozone in the Antarctica?

5.  Is there really a “hole” in the ozone layer?

6.  What are the chemical compounds that are primarily responsible for depleting stratospheric ozone?  What are the source(s) of these chemicals?

7.  Why is ozone depletion greater over Antarctica than over other parts of the world?

8. What was the name of the international agreement aimed at stopping the production of ozone depleting chemicals?  Has it been successful?

9. Explain how the agreement referred to in question 8 benefited climate as well as the ozone layer.

10.  What are hydrofluorocarbons and what is their impact on climate?

11.  Discuss some of the feedbacks between climate and the ozone hole.

Stratospheric Vs. Tropospheric Ozone

It is important to distinguish between stratospheric ozone and tropospheric ozone.

Stratospheric ozone

• “good” ozone

• naturally occurring 

• shields the Earth from incoming UV rays; the only substance in the atmosphere that absorbs the most energetic of UV rays, UV-C and UV-B.

• interacts with Earth’s climate system; stratospheric ozone’s primary influence on climate is through its impact on stratospheric temperature; higher ozone concentrations mean higher temperatures, and stratospheric temperature impacts wind currents on Earth’s surface.

• not regulated by the CAA, but chemicals responsible for depleting it are

Tropospheric ozone

• “bad” ozone

• secondary pollutant formed by chemical reactions between emissions from human activities and sunlight

• primary component of smog

• negative impacts on human respiratory system

• negative impacts on plants

• greenhouse gas that contributes to global warming

• regulated as a criteria pollutant by the CAA

There are circumstances where stratospheric ozone can intrude into the troposphere and thus contribute to ozone pollution.  

Watch the short video below for an example of this phenomenon and NASA’s work to create visualizations of it.

Link:Stratospheric Ozone Intrusion

(Schindler, 2014)

• Around the turn of the 20th century refrigerators used toxic gases as refrigerants. There was a string of fatalities in the 1920s due to leakage of the toxic gases, which led to the search for safer compounds to use as refrigerants. This search culminated in the synthesis of the first CFCs in 1928.

• DuPont and General Motors teamed up and started selling CFCs under the trade name, Freon, in the 1930's.

• By 1935 8 million refrigerators that used Freon had been sold in the United States.

• In 1932 the first self-contained home air conditioning unit was sold, and it used Freon.

• Beginning around 1950, CFCs started to be used as the propellants in aerosol spray cans for things like hair spray and bug spray.

• Eventually global annual CFC production grew to over 1 million metric tons, and annual sales exceeded $1 billion.

• The first study to show that CFCs breakdown ozone was conducted in 1974.

• The first study that revealed an “ozone hole” was in 1985.

• The Montreal Protocol to restrict the production of CFCs was signed in 1987.

• As a result of the Montreal Protocol, the production of CFCs was phased out world-wide in 2010.

• There have been several alternatives to CFCs developed including hydrofluorocarbons (HFCs), sulfur hexafluoride (SF6), and perfluorocarbons (PFCs). As mentioned in the video above, these newer compounds do not deplete ozone, but they are powerful greenhouse gases.

• CFCs are have the greatest ozone depleting capacity, but they are not the only compounds that deplete ozone. Other ozone depleting compounds include methyl bromide and carbon tetrachloride.

Note the decline in atmospheric concentrations of ozone depleting substances due to the Montreal Protocol in the following figure. 

Also note the increase in concentrations in the CFC alternative, SF6.

To wrap up our discussion on the ozone layer and transition into a discussion about climate change, let’s read an article about a recent international agreement to phase out one of the common replacements for CFCs, HFCs. Be sure to reflect on the questions listed beneath the article. 

Link: 140 countries will phase out HFCs. What are these and why do they matter? - The Washington Post 

(Ovodenko, 2014)

Questions To Reflect On: 

1. What is name of the new agreement to phase out HFCs?

2. What existing international treaty is the agreement being amended to?

3. TRUE or FALSE: HFCs deplete the ozone layer.

4. TRUE or FALSE: HFCs contribute to global warming.

5. Briefly summarize why the phase out of HFCs was included in treaties dealing with ozone rather than treaties dealing with climate change.

6. TRUE or FALSE: Chemical companies are against regulating HFCs rather than developing climate-friendly alternatives to HFCs.

7. Studies show that banning HFCs worldwide could prevent an increase of _______ F  over the next century.

15.2 Human Impact On Climate

Greenhouse Gases

There are a handful of gases that contribute to the greenhouse effect. Carbon dioxide, methane, nitrous oxide, and water vapor are all naturally occurring greenhouse gases; however, as you know, human activities have drastically increased the concentrations of these gases above natural levels.

CFCs and HFCs are manmade compounds that are potent greenhouse gases. As mentioned above, SF6 is also a very potent greenhouse gas.  Very small amounts of SF6 occur naturally, but for all intents and purposes, most of the SF6 in the atmosphere is man-made.  Finally,  tropospheric ozone, which is a byproduct of human air pollution is also a greenhouse gas.

Each gas contributes differently to global warming depending on 1) its capacity to absorb and re-radiate heat and 2) how long it stays in the atmosphere. In order to quantify the impact a gas has on global warming, we use a measure called Global Warming Potential (GWP).

In short, the Global Warming Potential of a gas is a measure of the potential for a unit mass of the gas to cause global warming relative to a unit mass of carbon dioxide.

The table below shows a wealth of information about the various greenhouse gases including their pre- and post-industrial concentrations, their GWP, and their atmospheric lifetime.  Carbon dioxide gets the most attention of all of the greenhouse gases; this is because its concentration is so high and because our use of fossil fuels releases it in large quantities.  Note that the man-made CFCs, HFCs, and SF6 all have very low atmospheric concentrations.  However, their GWP is 1000’s of times greater than that of CO2, and because they are such stable molecules they stay in the atmosphere for a very long time. 

Anthropogenic Drivers Of Climate Change

Of more interest for this class and our topic, Human Impact on Climate, are the anthropogenic drivers of climate change, some of which are outlined below.

Increase in the concentrations of greenhouse gases

Carbon Dioxide

• Most important greenhouse gas

• Contributes about 64% of the total radiative forcing by greenhouse gases

• Approximately 50% of human emissions are absorbed in the biosphere and oceans; the rest remains in the atmosphere for hundreds to thousands of years

• Since 1750, concentration in the atmosphere has increased by 40%

Methane

• 2nd most significant greenhouse gas

• Contributes about 18% of the total radiative forcing by greenhouse gases

• Approximately 40% of atmospheric methane comes from natural sources with the remaining 60% coming from human activities (natural gas production, livestock production, landfills, mining)

• Stays in the atmosphere for about 12 years

• Since 1750, concentration in the atmosphere has increased by 150%

Nitrous Oxide

• 3rd most significant greenhouse gas

• Contributes about 6% of the total radiative forcing by greenhouse gases

• Approximately 60% of atmospheric NO2 comes from natural sources with the remaining 40% coming from human activities (fossil fuel combustion, agriculture, industrial processes)

• Stays in the atmosphere for a few hundred years

• Since 1750, concentration in the atmosphere has increased by 20%

Deforestation

Tying back to one of our earlier units, deforestation also contributes significantly to climate change. For an introduction to deforestation and climate change, read through the article below. Be sure to reflect on the questions listed beneath the article.

Link: Deforestation and Its Extreme Effect on Global Warming - Scientific American 

(Scientific America, 2012) 

Questions To Reflect On:

1. According to the article which adds more CO2 to the atmosphere, deforestation or vehicle emissions?

2. Explain why deforestation adds carbon to the atmosphere.

3. Discuss why it is difficult to convince rainforest residents to engage in conservation.

4. What is REDD and how does it work? Has it been successful?

The Current State Of Climate Change

There is an abundance of statistics and graphics and news stories citing evidence of climate change and detailing the consequences of climate change. The article below very briefly covers some of the main evidence for and impacts of climate change. It also reinforces many of the above concepts. Click on the blue button below to access the article. Read through the article and reflect on the questions below.

Link:12 Graphics that Contain Everything You Need to Know about Climate Change - Scientific American Blog Network 

(Scientific American, 2014) 

Questions To Reflect On:

1. What does IPCC stand for?

2. TRUE or FALSE: The IPCC’s predictions for greenhouse gas emissions have been pretty much on target with actual emissions.

3. How have global surface temperatures changed since 1850?

4. What stands out about the global surface temperatures of the last three decades?

5. Define radiative forcing.

6. What are the top three contributors to the positive radiative forcing, which is causing warming?

7. According to the article, what are the four main contributors to the rising CO2 concentrations.

8. “The key to combating climate change is keeping the amount of carbon in the atmosphere from ___________________ - and potentially ____________________ it from present concentrations.”

9. According to the article, what is one of the most pressing challenges that humans will face due to climate change?

10. What percent of the world’s population lives within 100 km of a coastline?

11. Explain one way that climate change could impact freshwater resources.

Some Thoughts on Climate Modeling

Because the climate predictions that are reported on the news all come from climate models, it is important to have some understanding of modeling. Watch the following TED talk for a discussion about climate models. Be sure to reflect on the questions beneath the article.

Link: Gavin Schmidt: The emergent patterns of climate change | TED Talk 

(Schmidt, 2014) 

Questions To Reflect On:

1. Discuss the variety of spatial scales of the processes that influence climate.

2. How do we generally deal with sub-scale processes (those processes that occur at smaller scales than we are able to model)?

3. Do current climate models adequately cover the range of scales needed to represent all of the various processes that influence climate?

4. Roughly how many lines of code do current climate models have?

5. TRUE or FALSE, climate models include code to solve equations that describe fundamental physical processes.

6. The speaker gives examples of several pieces of the climate puzzle, which are essentially different processes that need to be included to accurately model climate. List the “puzzle pieces” he mentions.

7. Just something to notice - when the speaker is talking about different ways to “kick the climate system”, most of the things he mentions are things that we have covered in class. He is emphasizing the types of earth systems interactions that I have tried to weave into this course.

8. TRUE or FALSE: Models are always wrong.

9. If models are always wrong, what is the purpose of modeling?

END OF MODULE 15