Lesson 7 Climate Change

  Introduction

D7.1 Humans affect Earth

News feeds and social media are littered with articles, comments, and memes about climate change, but do you really understand what climate change is all about? The consensus among scientists is that Earth is experiencing a global climate change, but there are others who claim that climate change is not real. Who do you believe?

In this lesson, you will learn what climate change is and what causes it. You will examine human activities contributing to climate change. You will also study evidence showing that these human activities affect climate change.

You will look at historical climate changes and investigate how these climate changes differ from the present climate change.

  Targets

• investigate past changes in Earth’s climate
• explain the natural and enhanced greenhouse effect and the role of various gases in them
• examine the evidence that identifies how human actions on biomes have the potential to change global climate

  Watch This

  Past Climate Change

Earth has experienced climate change in the past; in fact, these changes seem to cycle over thousands of years. Ice ages lasting 12 000 to 60 000 years have alternated with warm periods called interglacial periods. Earth is currently in an interglacial period that started about 11 500 years ago.

We know about past climate change because of evidence left in different parts of Earth, including but not limited to trees, glaciers, oceans, coral reefs, and rocks.

Glacier ice is layered in years.  Air pockets found in different layers of ice give us a climate record that goes back as much as 800 000 years. By taking samples of the air found in  air pockets, we can get a detailed look at what the atmosphere was like during the time that layer was formed. The different particles found in the ice itself give scientists a clue as to the average global temperature at that time.

We think that data from ice cores is reliable because the findings about climate are confirmed by other data sources.  Varves from sedimentary rock deposited on lake bottoms show the same results.

Climate change in the past has been due to small shifts in how the Earth orbits the sun, shifts in Earth’s tilt, changes in Earth’s atmosphere or surface over time, and variations in the sun’s energy. These are all-natural phenomenon that caused the global temperature of Earth to warm up or cool down. These changes occurred over thousands of years; in fact, evidence suggests that as Earth moved out of ice ages, the global temperature rose 4 to 7 ˚C over 5 000 years. Climate change has always been a natural but very slow process, allowing Earth’s biosphere time to adjust to the changes occurring.

  Digging Deeper

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© Mauricio Antón, via Wikimedia Commons
D7.8 Ice age climate

Did you know there is a field of science called paleoclimatology? This is the study of past climates, and it is a relatively new field of science. Scientists hope by understanding past climate changes and how they occurred, we can better predict and understand the current climate changes. Go to the following link for more information on paleoclimatology. https://earthobservatory.nasa.gov/Features/Paleoclimatology/paleoclimatology_intro.php

Learn More

Earth's Tilt

© NASA
D7.4 Earth’s changing tilt

Earth’s tilt wobbles between 22.1˚ and 24.5˚. At Earth’s maximum tilt, the poles receive more solar insolation, creating warmer climates across the globe. At the minimum tilt, the poles receive less insolation, so the climates are colder.

Earth's Orbit

The shape of Earth’s orbit changes over the course of about 100 000 years. It changes from a perfect circle to an oval every 50 000 years. This affects the amount of sun the earth receives during different seasons.

D7.5 Earth’s changing orbit

Continental Drift

D7.6 Continental drift

The continental drift theory suggests that the continents have moved over the last 225 million years. At one point, all the contents fit together to form one super continent called Pangea. Pangea then split apart, and the continents drifted to the locations they are currently at. The change in the location of the continents changed the flow of the ocean currents and therefore changed how thermal energy was transferred through the ocean.

Feedback Loops

D7.7 A feedback loop

Earth’s responses can increase the effects of climate change. For example, as the earth warms, more water evaporates into the atmosphere. This evaporated water results in the formation of more clouds, increasing the cloud cover. The cloud cover will block solar radiation from reaching the earth, cooling the temperature down. The cloud cover will also block thermal energy emitted from Earth from escaping to space, increasing the temperature.

Another natural phenomenon is the amount of snow cover. As the earth cools, more snow and ice are formed on its surface. This increase in snow and ice will increase the albedo, causing more solar radiation to be reflected back into space. This would cause Earth to continue to cool, creating more snow and ice.

  Try This

Analyzing Tree Rings

• Background Information
  
• Procedure
  
• Analysis
  

Dendroclimatologists have used the growth rings in trees to gather records of Earth’s past climate data from as far back as 8 000 years. They do this by measuring the width of each of the growth rings on the trees. The wider the growth ring, the wetter the year and the longer the growing season. Tree rings are also affected by a variety of other factors, such as cloud cover, nutrients, and pests. When climatologists study the growth rings, they need to take all of these factors into account.

Click the procedure tab to continue. 

1. Study the tree rings in image D7.9. Label each of the growth rings with a number, with 1 being the centre growth ring. The oldest part of the tree will be in the centre.
2. Measure the width of each growth ring with a ruler and record your measurements below. You can use a rule against your screen or use this image with a ruler attached.
   
   

   Ring Number	Ring Width (cm)
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17

   
   
3. Click the analysis tab to complete the analysis questions

D7.9 Tree cross-section

1. How did the size of the tree rings change as the tree got older? What does that tell you about the climate as the tree grew?
   
   
   Check your work.
   

   The tree rings got smaller as the tree got older. This tells us that the climate became drier as time went on. The growing season may have also gotten shorter due to the climate cooling. Another option is that the number of pests bothering the tree increased due to warmer winters (for example, the pine beetle).
   
2. If this tree was from where you live, what do you think could have caused the pattern of these growth rings?
   
   
   Check your work.
   

   Your answer will vary with where you live. Most of Alberta has been seeing a reduction in precipitation in both winter and summer over the past few years. This could account for smaller growth rings, as the tree does not have enough water to grow normally. An increase in pests could also account for smaller growth rings in heavily forested areas due to warmer winters. These warmer winters do not kill off the pests as the colder winters would have in the past. As trees get bigger, they require more nutrients to grow, so they generally do not grow as much as they get older. This is especially true of trees in areas where there are lots of other plants, such as other trees or crops.
   

  Take Notes

  Practice Questions

1. What period of climate does Earth currently have? How long have we been in this stage for?
   
   
   Check your work.
   

   Earth currently has an interglacial climate. We have been in this interglacial climate for approximately 11 500 years.
2. Why does natural climate change occur?
   
   
   Check your work.
   

   Climate change occurs naturally through small changes in Earth’s orbit, tilt, surface, and atmosphere. It also changes as a response to previous climate changes, such as the buildup of snow and ice increasing the albedo and causing the formation of more snow and ice.
   

  Current Climate Change

D7.10 Temperature rising

The climate change we are seeing today is happening at an accelerated rate when compared to past climate change. In the past, temperature changes of 4 to 7 ˚C happened over thousands of years. In the past century (100 years), our current global temperature changed 0.7 ˚C. That is approximately 10 times faster than previous temperature increases!

According to NASA’s Earth Observatory, current models suggest Earth will warm between 2 ˚C and 6 ˚C in the next century. This predicted rate of warming is a whopping 20 times faster than past climate change.

D7.12 Industrial revolution

We have learned natural phenomena can affect climate, but those natural factors have remained relatively unchanged in the last 100 years. So what could be the cause of this increased pace in climate change? The only difference is human activity. Since the industrial revolution, humans have played a much larger role in changing the environment around us. During that time, our cities started to expand and we started to create more emissions that were released into the atmosphere. Using complex models, changes in global temperature can be attributed to natural events until about 1950. After that, we can only explain these changes if we include human activity and the emissions we create.

Please note: Earthobservatory.nasa.gov was used as a reference for the information on this page.

  Watch This

  Take Notes

  Practice Questions

1. How does the climate change we are currently experiencing differ from past climate changes?
   
   
   Check your work.
   

   The current climate change is occurring much faster than previous climate changes.
   

  The Greenhouse Effect

© US EPA, via Wikimedia Commons 
D7.13 The greenhouse effect

The natural greenhouse effect is the term used to describe the absorption of thermal energy by the atmosphere. As we studied previously in this unit, this happens naturally and it helps to keep Earth’s climate warm enough for organisms to survive. Without the greenhouse effect, the temperature of Earth would be about 33 ˚C lower. Remember, different gases have different abilities to absorb thermal energy. Some gases absorb large amounts of thermal energy, while others do not absorb any. Gases that absorb and re-emit large amounts of thermal energy are called greenhouse gases.

An increase in these greenhouse gases has led to what is known as the enhanced greenhouse effect. This is the main cause of the increased climate change that Earth is undergoing. Let’s look at each greenhouse gas in detail.

Water Vapour (H₂O)

D7.14 Increase in water evaporation

Water vapour is the most natural of the greenhouse gases and is one that, generally, humans have little effect on. Water is the main cause of the natural greenhouse effect; it causes about two-thirds of this effect and is key to keeping temperatures on Earth habitable. The problem lies in what happens to water vapour as the climate warms unnaturally. As other greenhouse gases increase and the enhanced greenhouse effect takes place, more water evaporates into the atmosphere. This increases the amount of water vapour in the atmosphere and increases the contribution of water vapour to the greenhouse effect. This continues to warm global temperatures, causing more water to evaporate and the cycle to continue. NASA’s Earth Observatory website states that if this trend continues, water vapour has the ability to double the warming caused by carbon dioxide alone. This means that the extra water evaporating into the atmosphere due to the warming caused by carbon dioxide will cause the warming to double.

Previously in this lesson, it was mentioned that the more water vapour entering the atmosphere, the more clouds created. It was suggested clouds block sunlight and therefore cool the temperature of Earth. So this excess water vapour should balance itself out with the extra clouds created, right?

Unfortunately, it depends on where the clouds are created. If low clouds are created, this is definitely the case; however, studies have shown this extra water vapour is forming high clouds—clouds that sit higher in the atmosphere. These high clouds act like a greenhouse gas and block thermal energy from escaping back into space, enhancing the greenhouse effect.

D7.15 Low level clouds over prairies

Carbon Dioxide (CO₂)

The next biggest greenhouse gas is carbon dioxide, and this greenhouse gas is directly tied to human activity and the problem caused by an increase in water vapour in the atmosphere.

D7.16 Forest fire—a carbon source

There are carbon sources and carbon sinks. Carbon sources release carbon dioxide into the atmosphere. Some examples of carbon sources are forest fires, combustion of fossil fuels, such as oil and gas, and animals breathing. Carbon sinks remove carbon dioxide from the atmosphere. Forests and oceans are examples of carbon sinks, as the plants in forests use carbon dioxide for photosynthesis and carbon dioxide dissolves in oceans and lakes.

When carbon sources and carbon sinks are in equilibrium—meaning the amount of carbon dioxide released into the atmosphere is equal to the amount taken out of the atmosphere—the amount of carbon dioxide in the atmosphere remains stable. If this was the case, we would not be seeing the rapid climate change we are experiencing. Unfortunately, they are not equal.

Deforestation is the removal of forested areas on Earth, dramatically reducing carbon sinks. Large scale deforestation has been occurring for the last 200 years, as people migrate into forested land to create farms and as cities and urban centres have expanded. Deforestation is still a problem today. Deforestation occurs when the trees removed are not replaced. This occurs when trees are removed for agricultural reasons or for human habitat, not necessarily as part of the forestry industry.

Deforestation causes the balance between carbon sources and carbon sinks to shift. When there are more carbon sources than sinks, excess carbon dioxide is released into the atmosphere, increasing the greenhouse effect.

D7.17 Deforestation for agriculture

D7.18 Vehicle emissions

Other human activity has also changed this balance between carbon sources and sinks. Many human activities, such as driving vehicles, heating homes, and generating electricity, burn fossil fuels, which releases large amounts of carbon dioxide into the atmosphere, enhancing the greenhouse effect. In fact, carbon dioxide is the main emission released during fossil fuel combustion. Water vapour and nitrous oxide is also formed, and both of these enhance the greenhouse effect as well.

Carbon Dioxide and Climate Change Feedback

Right now, the carbon sinks are absorbing about half of the carbon dioxide released due to human activities. This is very important, as this slows the increase of carbon dioxide in the atmosphere, therefore slowing climate change. However, this may not be the case for much longer.

© US EPA, via Wikimedia Commons 
D7.19 Carbon sources larger than carbon sinks

The oceans play a huge role in absorbing the carbon dioxide being released into the atmosphere, as they are the main carbon sink. The problem is that as the oceans warm up due to climate change, they can hold less carbon dioxide. So as the climate warms due to carbon dioxide in the atmosphere, the oceans become warmer and can remove less carbon dioxide from the atmosphere, increasing the rate of climate change.

As the climate warms and places such as the tundra, which are normally frozen all year, start to thaw, carbon that had been trapped may be released into the atmosphere. The surrounding plants will help to absorb some of the extra carbon; however, once the plant takes up all the carbon it needs, it will not take up anymore. Once the plants reach their limit, all the carbon released from the melting permafrost will go into the atmosphere, enhancing the greenhouse effect.

Please note: Earthobservatory.nasa.gov was used as a reference for the information in this section.

Nitrous Oxide (N₂O)

D7.20 Coal burning power plant

Nitrous oxide is the next common greenhouse gas. The correct IUPAC name for this gas is dinitrogen monoxide, but it is commonly referred to as nitrous oxide. As noted above, nitrous oxide is released during the burning of fossil fuels though not to the same degree as carbon dioxide. Nitrous oxide is released anytime a substance is burned, as the oxygen needed for combustion comes from the atmosphere. Remember, the atmosphere contains 78% nitrogen, so the oxygen used often includes some nitrogen as well. This gas has enormous potential to enhance the greenhouse effect, but there is less of it being released into the atmosphere compared to carbon dioxide. An increase in nitrous oxide in the atmosphere has been observed since the start of the industrial revolution, with the biggest increase occurring in the last century. The concentration of nitrous oxide in the atmosphere is steadily increasing as our energy needs increase. Nitrous oxide contributes to about 6% of the enhanced greenhouse effect, and its concentration in the atmosphere has increased by 15% since 1800.

Agriculture is another source of the increase in nitrous oxide in the atmosphere. The manure and chemical fertilizers used release nitrous oxide into the atmosphere. This is an extremely common worldwide practice.

Methane (CH₄)

Methane is the third natural greenhouse gas affected by human activity. It does not last long in the atmosphere before it breaks down, and it has less potential to enhance the greenhouse effect than nitrous oxide, however, it contributes to 20% of the enhanced greenhouse effect. The concentration of methane in the atmosphere has increased by 146% since 1800. Methane is also known as natural gas, and it is a common fuel used in most Albertan homes.

D7.21 Sources of methane

Methane gas is released during the mining and drilling process for extracting fossil fuels. It can be leaked through the pipelines when transporting natural gas from one place to another, though efforts are made to stop this from happening. Methane is also released into the atmosphere by rice patties and the digestive systems of farm animals (as well as humans). As the amount of farming and energy resources needed to support a growing human population increases, the amount of methane released into the atmosphere increases as well.

Other sources of methane include decaying garbage in landfills, decaying vegetation in areas flooded by dams, and decaying organic material (such as dead plants and animals). About 60% of the methane released into the atmosphere is due to human activities.

Technology has improved around the capture of methane from landfills to be used for energy in homes. Landfills are the second largest cause of methane in the atmosphere, so this could be an important step in fighting climate change.

  Digging Deeper

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© U.S. Geological Survey, via Wikimedia Commons
D7.22 Discovered and inferred locations of methane hydrate

There is another form of methane being researched for energy purposes called methane hydrate. Methane hydrate is methane combined with water, and it is found mostly in very deep oceans. It needs a specific temperature and amount of pressure to form. The supply of methane hydrate could contain up to twice the amount of energy from the natural gas supply. Research is being done into how we can extract it without causing further harm to the environment. Go to the following link for more information on methane hydrate.

Learn More

Other Greenhouse Gases

Halocarbons are human made compounds containing halogens and carbon. The most common of these compounds are chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). These halocarbons have the largest potential to enhance the greenhouse effect. They were developed in the 1930s to be used as coolants in a variety of appliances and as propellants in aerosols. CFCs are particularly dangerous, because they also cause the thinning of the ozone layer. Because of this, the use of CFCs was banned in 1996 as part of the Montreal Protocol.

Ground-level ozone is another human-made problem. Ground-level ozone differs from the ozone layer. The ozone layer plays a part in the natural greenhouse effect and protects us from some of the sun’s more harmful rays, such as ultra-violet (UV) rays. Ground-level ozone enhances the greenhouse effect, increasing climate change. This compound is formed when emissions from vehicles, solvents, and oil-based paints react with heat and sunlight. These emissions are known as photochemical smog, and you can see this grey cloud hovering over a city on a sunny day.

D7.23 Photochemical smog over Vancouver

  Did You Know?

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© National Oceanic and Atmospheric Administration, via Wikimedia Commons
D7.24 Hurricanes Katia, Irma, and Jose in a row

The summer of 2017 was ranked the fifth most active hurricane season since 1851. It saw 17 named storms, with 6 classified as major hurricanes. These storms resulted in over 882 deaths, made Barbuda uninhabitable, and caused over $369.76 billion US dollars in damage. Experts agree climate change contributed to the increased activity, though it was not the only reason for it.

  Read This

  Practice Questions

1. What is the greenhouse effect? How do the natural and enhanced greenhouse effects differ?
   
   
   Check your work.
   

   The greenhouse effect is the process where thermal energy re-emitted by Earth is reflected back toward Earth’s surface, keeping the temperature at a habitable level. The enhanced greenhouse effect happens when more thermal energy than is needed is reflected back to Earth’s surface, causing the temperature to increase.
2. What are greenhouse gases, and how do they affect the greenhouse effect?
   
   
   Check your work.
   

   Greenhouse gases are the gases in the atmosphere that absorb and re-emit the thermal energy back toward Earth’s surface. The more greenhouse gases present, the greater the greenhouse effect.
3. How do humans affect the greenhouse effect? What evidence is there to support this?
   
   
   Check your work.
   

   Human activity since the 1800s has increased the concentration of greenhouse gases in the atmosphere, enhancing the greenhouse effect. Since the industrial revolution, humans have played a much larger role in changing the environment around us. During that time, our cities started to expand and we started to create more emissions that were released into the atmosphere. Using complex models, changes in global temperature can be attributed to natural events until about 1950. After which, we can only explain these changes if we include human activity and the emissions we create.

  Virtual Lab

Greenhouse Effect © Explore Learning

Background Information:

This lesson has talked about the greenhouse effect and how greenhouse gases play a part in that effect. It also talked about how human activities are increasing the amount of those greenhouse gases in the atmosphere. This Gizmo will help you see what happens as the percentage of greenhouse gases in the atmosphere increases.

Please note: if you scroll down while in the Gizmo you will see a list of questions. You DO NOT need to complete these questions. You are able to complete them for extra practice if you would like.
An assessment question is based on this activity!

• Procedure
  
• Analysis
  

1. Open the Gizmo by clicking on the play button. Print students can access the Gizmo in the Online Resources for Print Students section of their online course.

2. Change to the “GRAPH” tab found on the far right side of the Gizmo.

©Explore Learning
D7.25 Graph tab

3. Ensure that the greenhouse gas percentage is set to 10%.
4. Click on the play button and watch what happens on the graph.
5. Once you have seen a pattern emerge, click the pause button.
   

©Explore Learning
D7.26 Greenhouse gases percent

6. Take a screenshot of the pattern you see by clicking on the camera seen on in the upper right-hand corner of the graph.

©Explore Learning
D7.26a Camera icon

7. Increase the percentage of greenhouse gases to 50%.
8. Click the play button and watch what happens to the graph.
9. Once a pattern emerges, click the pause button and take another screenshot of the graph for your notes.
10. Increase the percentage of greenhouse gases to 90%.  Use the camera icon to take a screenshot for 4.5 Assignment.  Right click and save to a location you will remember.
    
11. Repeat steps 8 to 10.
12. Please return to the top of this page and click on analysis to complete the analysis questions.
    

©Explore Learning
D7.27 How to read the graph

1. Compare the H_out line on the three graphs you generated. What happened to the line when you increased the greenhouse gases in the atmosphere? Why does this happen?
   
   
   Check your work.
   

   The H_out line on the graph decreases when you increase the greenhouse gases in the atmosphere. This happens because the greenhouse gases trap the thermal energy trying to escape to space and reflect it back down to Earth’s surface. The more greenhouse gases in the atmosphere, the more thermal energy that ends up trapped near Earth’s surface.
2. Compare the temperature line in the three graphs you generated. What happens to the temperature as you increase the greenhouse gas percentage? Why does this happen?
   
   
   Check your work.
   

   You will answer this question in Formative Assessment D3.
3. Compare the H_in line in the three graphs you generated. Why does the H_in graph not change?
   
   
   Check your work.
   

   The H_in is the solar radiation from the sun. It does not change because the sun and the amount of radiation Earth receives from the sun are not changing. It is only how Earth is dealing with that solar radiation that is changing.
4. How is the greenhouse effect similar to the way the sun heats up an agricultural greenhouse? How is it different?
   
   
   Check your work.
   

   In both the greenhouse effect and a greenhouse, the solar radiation is being absorbed by plants and soil and then being re-emitted as thermal energy. In both cases, that thermal energy is then trapped by the glass or the greenhouse gases. In a greenhouse, the glass reflects all the heat back into the greenhouse, keeping it warm. In the greenhouse effect, the greenhouse gases absorb the thermal energy and reflect some if it back toward Earth’s surface. In the greenhouse effect, it is also more than just the plants and the soil that absorb the solar radiation. It is also absorbed by the atmosphere, the hydrosphere, the animals, and the lithosphere.

  Climate Change and Humans

D7.28 Emissions spelling CO₂

A main cause of climate change is the contribution human activities have made to the concentration of greenhouse gases in the atmosphere. By increasing the concentration of greenhouse gases in the atmosphere, we are creating an enhanced greenhouse effect. This enhanced greenhouse effect reflects more thermal energy than is needed back to the surface of Earth, causing a rise in global temperatures. This rise in temperatures then impacts the climates and biomes around the world. We will take a closer look at the impacts of the rise in global temperatures in the final lesson of this section.

In the next lesson, we will look at the international programs working to study and slow climate change.

  Problem-Solving Activity

Carbon Dioxide © NASA

4.5 Assignment

Unit 4 Formative Assessment Lesson 7