chapter 17: global change copyright © the mcgraw-hill companies, inc. permission required for...

Chapter 17: Global Change

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1. Alternative Climates, Alternative

2. Ozone and the Stratosphere

4. Greenhouse Gases and Global

3. CFCs and Ozone Depletion

Change

Choices

5. Modeling Global Climate Change

6. A Warmer World

7. What Can Be Done?

Learning Objectives• Students will explain concepts related to global change.• Students will describe characteristics of ozone in the atmosphere

in relation to components of the Earth system.• Students will compare and contrast global warming and the

greenhouse effect.• Students will explain how carbon dioxide moves between

components of the global carbon cycle.• Students will explain how climate forcings and feedbacks impact

climate.• Students will describe predictions for our future climate from

climate models.• Students will identify what can be done to reduce greenhouse

gases.• Students will clarify their own ideas about their role in Earth’s

future.

Alternative Climates, Alternative Choices

The Good Earth/Chapter 17: Global Change

The big question – how likely is it that events such as those depicted in movies like “The Day After Tomorrow” will actually happen?

If not in our lifetime, then when?

Will major global change effect our kids? Our grandkids? Our great-grandkids?

HOW MUCH SHOULD WE WORRY?



Ozone hole over Antarctica (below) and global temperature record (right). Are these two things related?

It is a common misconception that ozone depletion causes global warming. However, both are global-scale issues related to atmospheric composition – ozone in the stratosphere, and CO2 and some other greenhouse gases in the troposphere.



Americans don’t worry too much about global warming.

Governments still debate intensely over the validity of policies to address global warming.

Montreal Protocol was established to reduce use of ozone-depleting chemicals.

What steps are being taken to reduce carbon emissions?


Global Change Self-Reflection Survey

Answer the following questions as a means of uncovering what you already know about global change.

1. Respond to the following questions taken from recent polls:

i. How convinced are you that global warming is actually happening?

a. Completely convinced

b. Mostly convinced

c. Not so convinced

d. Not convinced at all

e. Not sure

Results from other respondents:

a. 23%; b. 36%; c. 24%; d. 16%; e. 2%




ii. What do you think about global warming?

a. It is an urgent problem that requires immediate government action.

b. It is a longer-term problem that requires more study.

c. It is not a problem.

d. I am unsure. Results from other respondents:

a. 38%; b. 58%; c. 3%; d. 1%




iii. Which of the following statements reflects your view of when the effects of global warming will begin to happen?

a. They have already begun to happen.

b. They will start happening within a few years.

c. They will start happening within your lifetime.

d. They will not happen within your lifetime, but they will affect the

future.

e. They will never happen.

f. No opinion.

Results from other respondents:

a. 54%; b. 5%; c. 10%; d. 19%; e. 9%; f. 3%



Make a list of at least three advantages and three disadvantages of an increase in temperatures in the region where you live. Then do the same for Earth as a whole.



From your existing knowledge about global warming, how do your personal actions contribute to or help reduce the potential for global warming?

Go back to the Table of Contents

Go to the next section: Ozone and the Stratosphere


Ozone and the Stratosphere


The ozone layer is Earth’s own sun block system that stops 97-99 % of the harmful incoming ultraviolet rays from reaching the planet’s surface.

3 types of ultraviolet radiation – UVA, UVB, and UVC

UVC – shortest wavelength, most dangerous, filtered out by atmosphere

UVA and UVB – cause skin cancer and wrinkles after repeated long-term exposure

- UV rays can penetrate your clothes- SPF 15 lotion blocks out ~92% of the UV that reaches Earth’s surface

Global Change Conceptest


Which of the following statements is the best analogy?

a)An umbrella is to rain as the stratosphere is to solar radiation.

b)An umbrella is to rain as the stratosphere is to ultraviolet radiation.

c)An umbrella is to rain as the stratospheric ozone is to solar radiation.

d)An umbrella is to rain as the stratospheric ozone is to ultraviolet radiation.



Formation of ozone is cyclical:

1. UV radiation breaks an O2 molecule into two separate O atoms.

2. An individual O atom combines with a whole O2 molecule to form an ozone molecule.

3. UVB strikes an ozone molecule and breaks it back down into an O2 molecule and an O atom.

This O atom is then free to combine with another O2 and make more ozone.

No long-term change in the concentration of ozone

occurs.



UV radiation is converted from light to heat by the destruction of oxygen molecules and ozone molecules.

Temperature rises with increasing altitude in the stratosphere.

The three steps of natural ozone production and destruction in the stratosphere:

(i) O2 + UV O + O (+ heat)

(ii) O2 + O O3

(iii) O3 + UV O2 + O (+ heat)

Global Change Checkpoint 17.2


Which of the following concept maps best represents the sequence of transformations associated with the formation and destruction of ozone in the stratosphere? Explain the reasoning behind your choice.



Dobson Units:

One DU = 0.01 mm (0.0004 inches)

Global variations in ozone concentrations, Jan. 2001. Stratospheric ozone concentrations are nearly constant over the tropics but become more concentrated and subject to larger seasonal variations at higher latitudes. Concentrations are greatest in Northern Hemisphere during its spring, and greatest in Southern Hemisphere during Northern Hemisphere fall. Concentrations are linked to atmospheric circulation patterns, temperature, and solar radiation reaching the Earth.

Complex stratospheric circulation patterns remove ozone from the tropics and deposit it at higher latitudes.

Global Change Checkpoint 17.3The following graph represents the variation in ozone concentrations over four cities: Darwin, Australia, 12°S; Melbourne, Australia, 37°S; San Francisco, USA, 37°N, London, UK, 55°N. Explain which city goes with each of the four plots, then sketch an estimated plot for the city where you live.



Go to the next section: CFCs and Ozone Depletion



CFCs and Ozone DepletionWhat are CFCs (chlorofluorocarbons)?

Volatile organic compounds used as aerosol propellants and refrigerants

Inert (non-reactive) gases that remain in the atmosphere for up to 200 years

Can be broken down by photolysis (UV radiation) which frees chlorine atoms from the CFCs

Chlorine atoms react with ozone destroying an ozone molecule and creating chlorine monoxide and oxygen:

Cl + O3 ClO + O2

Chlorine monoxide reacts with oxygen atoms freeing up another chlorine atom available for breaking down ozone

80% of chlorine in the stratosphere comes from CFCs

In 1978 per the Montreal Protocol the US banned aerosol sprays containing CFCs and phased out their production

CFCs and Ozone Depletion


Ozone is naturally reduced above Antarctica every spring, but reductions beyond the expected natural variation were noticed in 1985.

Ozone hole – not an actual hole, just an area of reduced ozone.

Ozone levels began to drop in the 1970’s.

During October (Southern Hemisphere spring) ozone concentrations over Antarctica drop to ~100 DU.


How would a scientist tell the difference between ozone loss due to chlorine from CFCs and loss due to chlorine from a volcanic eruption?




Why is ozone depletion concentrated over Antarctica?

• Unique weather patterns over Antarctica – polar vortex

• Temperatures below -112°F June through August

• Leads to formation of polar stratospheric clouds (water + nitric acid)

• Ice particles in these clouds provide surfaces on which chemical reactions can occur, including the release of chlorine by chlorine bearing compounds

• In spring (September through November) temperature rises, processes that produce ozone outpace destruction and ozone begins to increase

• No polar stratospheric clouds elsewhere means less ozone loss elsewhere

Ozone formation and destruction are temperature dependent phenomena



Students in a college earth science class are asked to concisely describe the relationship between CFCs and ozone destruction on an exam. Analyze the following four students’ responses and rank them from best to worst. Justify your answer choices.

a) CFCs are manufactured gases that destroy the ozone and produce oxygen.

b) Chlorine forms from the disintegration of manufactured gases. The chlorine reacts with ozone molecules to form two gases that cannot block incoming UV radiation.

c) Oxygen molecules are broken down by UV radiation to free oxygen atoms that combine with chlorine monoxide to form new oxygen molecules and free chlorine. Chlorine helps break down CFCs with UV radiation.

d) UV radiation breaks apart complex manufactured CFCs into its constituent atoms, including chlorine. Chlorine destroys ozone molecules at it cycles through a pair of reactions that produce free oxygen.

Finally, write your own answer to the question.



a. Chlorine concentrations in Earth’s atmosphere

b. Changes in CFC-11 concentrations in ppt

What do these two graphs tell you? What trends do you notice? What does this imply for our ozone layer’s future?

a.

b.


Go to the next section: Greenhouse Gases and Global Change


Greenhouse Gases and Global Change


Infrared radiation emitted from Earth’s surface is absorbed by water vapor, CO2, and other trace gases in the troposphere, creating a situation known as the greenhouse effect.

We like it because it keeps the average surface temperature of Earth ~59°F as opposed to 0°F.

Can have too much of a good thing – Venus has runaway greenhouse effect with average surface temperature of 885°F.

Facts:

The 20th century was the warmest in the last millennium

1990s were the warmest decade

1998 and 2005 tied as the warmest years in the last 1,000 years

There may be a debate about the severity of global warming, but one trend is undeniable – The concentration of greenhouse gases in the Earth’s atmosphere has steadily and measurably increased over

the past two centuries.



Carbon dioxide variations with time. Can you explain at least two things that the graph is telling us? What strikes you?



Key points:

1.Greenhouse gases help warm the planet.

2.Global concentrations of greenhouse gases have increased.

3.Average global temperatures have increased by 0.8°C (1.4°F) since 1860.

4.Population growth will contribute to increased concentrations of greenhouse gases in the future (projected to increase to about 10 billion people by 2100).



What is the difference between the greenhouse effect and global warming?



Carbon is in constant flux between all of Earth’s components

Atmosphere – both a sink and a source of carbon compounds and carbon based gases

Carbon enters atmosphere via:

respiration (animals exhaling CO2)

the burning of forests

the decay of dead organisms

burning of fossil fuels

natural volcanic activity

release of dissolved gases from the ocean



Atmosphere – both a sink and a source of carbon compounds and carbon based gases

Carbon leaves atmosphere via:

photosynthesis (used by plants)

rock formation (limestone)

absorption by the ocean

other biological processes

Overall, more carbon enters than exits the atmosphere by about 3.4 billion tons per

year!



Variations in carbon dioxide concentrations.

What two trends do you notice? How do you explain each one?



Saw tooth pattern = annual (seasonal) fluctuations in CO2 due to plant activity

Overall increasing trend = Build up of CO2 in atmosphere mainly due to human activities

Where on Earth would you expect to see the most pronounced seasonal CO2 variations? Why?



Hydrosphere – Oceans act as a carbon sink by absorbing more gas than they release

Oceans retain an additional 2 billion tons of carbon per year

The amount of CO2 oceans can absorb increases with

decreasing temperature and increasing wind speed

Wave action helps by creating bubbles that transfer gas from

air to water

CO2 falls in streams as acid rain and enters the oceans via

runoff

Carbon is carried to deep ocean in cold sinking currents and

remain for more than 1,000 years (long term reservoir)

CO2 is released back to atmosphere as warm water rises,

like bubbles out of a warm can of soda



Biosphere – Interacts with all other parts of the earth system through the carbon cycle

Plants extract CO2 from atmosphere by photosynthesis

Animals eat plants thereby consuming carbon

Carbon is returned to atmosphere when organisms die

Carbon can be held for millions of years if organic remains

are buried and converted to fossil fuel deposits (coal,

oil, natural gas)

Carbon is retained in some marine animals as part of their

shells, skeletons

Dead marine organisms sink, getting buried, locked in

sedimentary rocks, locking away their carbon



Geosphere – The largest sinks for carbon on the planet are rocks and minerals of the solid earth

Most is present as an element of calcium carbonate (limestone)

When limestone undergoes chemical weathering it releases

CO2 to the atmosphere

Chemical weathering is caused by acid rain, which takes CO2

out of the atmosphere

Some carbon is stored in fossil fuel deposits formed from

decayed organic material



Overall, CO2 in the atmosphere remained constant at 280 ppm on a global scale for several centuries prior to the industrial revolution.

Anthropogenic emissions of greenhouse gases such as CO2 rapidly increased in recent decades.

Most anthropogenic emissions come from consumption of fossil fuels and deforestation.

About half of what we produce is taken back into carbon sinks in biosphere and oceans – the rest is left in atmosphere.



Use the concept map provided here to illustrate the natural global carbon cycle by showing how carbon is transferred among the components of the earth system.



Principle U.S. greenhouse gases.

Water vapor accounts for most of the natural greenhouse effect, but human produced water vapor is not a factor in global warming.



Why do we burn fossil fuels?

Produces energy for things like:

Residential heat

Residential light

Gasoline for transportation

Power for industry

Which fossil fuel produces the most CO2?

COAL

OIL

NATURAL GASDistribution of global carbon emissions. How would you expect this figure to change over the next 50 years?



GWP (global warming potential) of a gas depends on its ability to hold heat AND how long it stays in the atmosphere.

CO2 has a longer lifetime (decades to hundreds of years) but absorbs less heat.

Methane absorbs a lot of heat, but remains in the atmosphere for much shorter time periods.GWP of methane is 21 times greater than that of CO2.



Where are most greenhouse gases concentrated?

• Initially, they are concentrated where there is more human activity.

• Atmospheric circulation patterns thoroughly mix the gases and distribute them throughout the troposphere.

• Greenhouse gas concentrations are remarkably uniform worldwide.

• The VAST majority of greenhouse gas emissions come from developed nations

(76%) with 25% coming from the U.S. alone.



Review the following three scenarios and discuss the implications for global greenhouse gas emissions. Then complete the graph show here to show how global carbon emissions would change over the next century for each

scenario. We are more interested in the trends than the absolute values for each scenario.

40

30

20

10

Year2000 2050 2100

Scenario A: Global population peaks around 9 billion in 2050 and declines thereafter. New technologies are rapidly introduced, and economic disparities between regions are substantially reduced. Fossil fuels continue to supply most of Earth's energy.

Global Change Checkpoint 17.12 continued

The Good Earth/Chapter 17: Global ChangeThe Good Earth/Chapter 17: Global Change

Complete the graph show here to show how global carbon emissions would change over the next century for scenario b. We are more interested in the

trends than the absolute values for each scenario.

40

30

20

10

Year2000 2050 2100

Scenario B: Global population continues to increase throughout the twenty first century (11 billion by 2050). Disparities in the economic growth of regions persist, and technological change occurs slowly. The energy supply gradually changes from fossil fuels toward alternative energy sources.


The Good Earth/Chapter 17: Global ChangeThe Good Earth/Chapter 17: Global ChangeThe Good Earth/Chapter 17: Global Change

Complete the graph show here to show how global carbon emissions would change over the next century for scenario c. We are more interested in the

trends than the absolute values for each scenario.

40

30

20

10

Year2000 2050 2100

Scenario C: Global population peaks around 9 billion in 2050 and declines thereafter. Economies rapidly become service-and-information oriented, income disparities decrease, and energy technologies that do not rely on fossil fuels are introduced.


Go to the next section: Modeling Global Climate Change


Modeling Global Climate Change


Forcings and Feedbacks:

Example – Sunburns

Sunburn is caused by sunlight interacting with skin cells.

Sunlight is the forcing mechanism, or cause.

The sunburn is feedback (a reaction).

Forcings and feedbacks are important parts of climate change.



Sunlight is scattered, absorbed, and/or reflected by Earth

More reflected = cooling More absorbed = warming

Earth's radiation balance

~1/3 is reflected

The rest is absorbed by atmosphere and land and water of Earth's surface

Infrared is absorbed and re-emitted toward Earth's surface by greenhouse gases



Climate forcing : Any phenomenon that causes a change in the global solar radiation balance.

-positive forcings lead to global warming, negative forcings lead

to global cooling

Examples:

Positive forcings: - More solar energy reaches Earth's surface

- More energy is absorbed by the addition of

greenhouse gases

Negative forcings: - Volcanic ash reflects light back into space

- Increased ice cover causes more reflection

off Earth's surface



Which of the above has the strongest affect on warming the climate? Why is this significant?

Why are volcanic aerosols both a positive and a negative forcing agent?



Aerosols are tiny reflective particles – makes them a negative forcing mechanism.

Some black particles absorb solar radiation and can cause warming.

Warming or cooling caused by forcings leads to other climatic feedbacks that can exaggerate or reduce temperature changes.Examples –

Warmer climate = more evaporation = increased greenhouse effect = more warming (POSITIVE FEEDBACK)

Warmer climate = more evaporation = more cloud cover = more reflection of solar radiation = cooling (NEGATIVE FEEDBACK)

So, addition of water vapor may contribute both positive and negative feedbacks to warming.



Scientists hypothesize that ~40% of global temperature changes are due to forcings, and feedbacks explain the rest.

Predicting climate change is hard due to multiple, and sometimes competing, forcings and feedbacks that occur simultaneously.

Global Change Conceptest


Where would you expect to see the most significant cooling effects due to aerosols? Explain your answer choice.

a) Near the poles

b) Around the equator

c) Between 30° and 60°N latitudes

d) Between 30° and 60°S latitudes



Explain the Milankovitch cycles described in Chapter 16 in terms of a climate forcing.



Scientists use sophisticated computer models that use millions of calculations to try to simulate climate factors over the entire earth system. Modern models seek to represent all key factors:

Incoming solar radiation

Outgoing radiation

Wind speed and direction

Cloud types

Precipitation types and amounts

Changes in dimensions ice sheets

Vegetation types

Atmospheric gas concentrations

Temperature stratification of the ocean

Continental topography

Figure 17.16 a



Models divide Earth's surface into a grid, each square represents the base of an atmospheric column divided into levels.

Models calculate natural phenomena. They characterize the conditions in each square on the grid and then set the model in motion at certain time intervals to simulate climate evolution.



Accuracy of the models?

They all tend to generate the same major trends that are observed in actual climate data.

Multiple models produce similar results. Global mean temperature change models for three scenarios:

Rapid economic growth, reduction in regional income variations.

Lower economic growth and same regional economic patterns.

Lower population growth with less economic growth than A1.



Explain why computer climate models are really "earth system" models.


Go to the next section: A Warmer World


A Warmer World


It is unlikely that we will be able to substantially reduce anthropogenic greenhouse gas emissions in the near future.

We must prepare to adjust to environmental changes associated with a warmer world.

Models predict that industrialization and resource use associated with rapid economic growth will have a more significant impact on global warming that population growth.

Predicted temperature changes are averages and mask the fact that temperatures could increase more than 18°F in some places and fall in other places.

Example – Warming causes melting of Greenland ice contributes fresh water to ocean, affecting Gulf Stream, cooling Europe

Most models predict greater temperature increases in northern latitudes and potential cooling in parts of the Southern Hemisphere

A Warmer World


Modeled changes in global surface air temperatures for 2070-2100.



Identify three actions a private citizen could take to reduce the amount of greenhouse gases produced on his or her behalf.

A Warmer World


Think about this:

What would you do if temperatures here increased by an average of 10°F?

Most recent research indicates that changes will be most extreme in developing nations who may not have the resources to deal with them.

Wealthy nations (who produce most of the greenhouse gases) will be less affected, and more able to deal with the changes.

We can crank our A/C – can everybody?

A Warmer World


Evaporation and precipitation will increase due to warming, but extra rainfall will not be distributed evenly around the globe. Higher for equatorial regions and for oceans vs. continents.

A Warmer World


Global sea level will rise by an average of 16 inches causing coastal flooding. This is caused by melting ice as well as thermal expansion of ocean water.

A Warmer World


If the West Antarctica ice sheet were to completely melt, raising global sea level by ~5 meters, most of southern Florida would disappear beneath the waves.

Changing climate will increase the severity of storms and heat waves.

A drier climate could alter the balance of water resources. Less water for agriculture could alter land use patterns. Lower stream discharges can affect hydroelectric power resources.

Warmer climates may replace some snow with rain – in spring, less snowmelt may change water sources for people who rely on snowmelt for their water.

Agricultural production will increase in some regions, decrease in others. This problem is more threatening for small developing countries with large populations to feed.

Shifting ecosystems – migration of plants to warmer temperatures, replacing native species, removing food sources for some animals.



Review the following descriptions of global warming and rank them in order of accuracy (1=most accurate, 5=least accurate).

___ Global warming is the gradual warming of Earth due to the greenhouse effect.

___ Global warming is a gradual, long-term increase in the temperature of Earth due to an increase in the concentration of trace atmospheric gases such as carbon dioxide that absorb heat from Earth's surface.

___ Global warming occurs when the temperature of Earth slowly increases because a layer of chemicals in the atmosphere absorbs more heat than normal.

___ Global warming is the result of the ozone layer in the atmosphere becoming thinner due to certain chemicals we use. This causes more solar radiation to reach Earth's surface, leading to higher average temperatures.

___ Global warming is the warming of climate over many years as a result of natural phenomena, such as volcanic eruptions, that trap heat close to Earth's surface.

Describe the criteria you used to rank the definitions and explain why you ranked them as you did.


Go to the next section: What Can Be Done?


What Can Be Done?


Global warming is complex. Should we do anything?

People do not appear to be directly threatened during their lifetimes.

Some countries might benefit from the warming.

Earth was much hotter in the past (Dinosaur times – Hothouse Earth).

In 1992 nations pledged to reduce emissions by 200 – it didn't happen.

1997 – Kyoto protocol – represents an agreement among developed nations to reduce greenhouse emissions to 1990 levels by 2008 – 2012, and 6-8% lower in following years.

Kyoto protocol is supported by more than 120 countries

Who doesn't support it? You guessed it – The U.S., for fear it may do harm to our economy. (Australia does not

support it either)

What Can Be Done?


The U.S. (Government's) Position:

We as a nation should (1) be consistent with the goal of stabilizing greenhouse gas concentrations in the atmosphere; (2) be sufficiently flexible to allow for new findings; (3) support continued economic growth and prosperity; (4) provide market-based incentives; (5) incorporate technological advances; and (6) promote global participation. The President's decision to take a deeper look at climate change policy arose from the recognition that the international dialogue begun to date lacked the requisite participatory breadth for a global response to climate change.

What does this mean? What technological advances are they talking about? This implies a non-governmental solution using a yet-to-be developed technology.

What Can Be Done?


Some options that have been proposed:

- Alter Earth's energy balance by reflecting incoming solar radiation using fleets of silver balloons or giant mirrors in the atmosphere.

-Carbon sequestration, the trapping of carbon in natural or artificial storage reservoirs.

-Adding tiny particles of iron to the oceans to spur growth of plankton, who extract CO2 from the oceans.

Problems?

-How do we get the mirrors up there? How do they stay up there?

-Assumes we can trap carbon produced by human activity.

-What if there is a catastrophic release of this trapped gas?

-Altering one part of the earth system to remedy human-induced changes on another could prove tricky or not useful at all.

What Can Be Done?


Earth can repair itself, but not on human timescales.

It would take up to millions of years for carbon concentrations in the atmosphere to return to natural levels.

Developing nations are pushing hard to raise their economies by expanding their use of fossil fuels increased CO2 emissions.

China will surpass the U.S. as the world’s greatest producer of greenhouse gases in the next few decades.

Just to maintain carbon dioxide at its present levels would require that we either reduce our greenhouse gas emissions by half, or substantially increase the uptake of these gases in natural or artificial reservoirs.



Explain how the comment “Earth can take care of itself” in the context of global warming relates to the concept of “deep time” discussed in Chapter 8.



What are some actions that could be taken to diminish the impact of global warming? Different groups of people have different perspectives on this issue. For some, solutions that would avert global warming may not be in their economic interests.

1) List actions each of the following interest groups could take to reduce global warming.

i. A major oil company

ii. A utility that burns coal to generate electricity

iii. A large car manufacturing company

iv. A company that manufactures wind turbines and solar energy panels

v. An international insurance company

vi. The Maldives, a small island nation with an average elevation of 1 meter

vii. A heavily populated developing nation (e.g. China, India)

viii. A heavily populated developed nation with a high standard of living (e.g. U.S)

ix. A family of four in the U.S. with two vehicles



Some interest groups are essentially powerless to do anything themselves and must rely on the actions of others. Consider the first two questions below and evaluate the answer for each group.

2) What would be the impact of global warming on each group?

3) How does the activity of each group impact future global warming?



Choose any three of the groups and answer these two questions for each group you choose:

4) If applicable, what steps could the group take to diminish the group’s impact on global warming?

5) What incentives would encourage the group to change its habits to reduce its contribution to future warming?

The End



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