1. Chapter 20: The Atmosphere, Climate and Global Warming

2. Overview Fundamental Global Warming Questions Weather and Climate
The Origin of the Global Warming Issue
The Atmosphere
How We Study Climate
The Greenhouse Effect
The Major Greenhouse Gases
Climate Change and Feedback Loops
Causes of Climate Change
The Oceans and Climate Change
Forecasting Climate Change
Potential Rates of Global Climate Change
Potential Environmental, Ecological and Human Effects of Global Warming
Adjusting to Potential Global Warming

3. Fundamental Questions About Global Warming
Concern arises from two pieces of evidence:
Increase in average surface temperature of the Earth from 1860 to the present
0.2˚C per decade since 1960
Increase in carbon dioxide concentrations in the atmosphere
Measured on Mauna Loa in Hawaii by Charles Keeling

6. Fundamental Questions About Global Warming
What is the origin of rapid warming in the geologic record?
Is the present rapid warming unprecedented or at least so rare that many living things will not be able to respond successfully to it?
To what extent, have people caused it?
What are likely to be the effects on people?
What are likely to be the effects on all life on Earth?
How can we make forecasts about it and other kinds of climate change?
What can we do to minimize potential negative effects?

7. Weather and Climate Weather Climate is the average weather
what’s happening now in the atmosphere near the earth’s surface
Temperature, pressure, cloudiness, precipitation, winds
Climate is the average weather
Usually refers to long periods of time
Classified mainly by latitude and wet/dry

9. The Climate is Always Changing
Climate has warmed and cooled may times in Earth’s history
Times of high temp involve relatively ice free periods
Times of low temp involve glacial events

11. The Origins of the Global Warming Issue
Relationship between chemistry of planet’s atmosphere and planet’s surface temperature
Certain gases trap heat energy and warm the planet
Since this idea was first introduce has stirred controversy

12. The Atmosphere Thin layer of gases that envelops Earth Comprised of
Held near the surface by gravitation and pushed upward by thermal energy.
Comprised of
Nitrogen (78%)
Oxygen (21%)
Argon (0.9%)
Carbon dioxide (0.03%)
Water vapor
Trace amounts of other gases/pollutants
Dynamic system

13. Structure of the Atmosphere
Made up of several vertical layers
Troposphere - bottom layer
Where weather occurs
Temperature decrease with elevation
At the top is tropopause - acts as a lid
Stratosphere - above the troposphere
Stratospheric ozone layer just above the tropopause
Protects again UV radiation

15. Atmospheric Processes
Processes generally defined by pressure, temperature, and water vapor content
Pressure is force per unit area
Caused by the weight of overlying atmospheric gases on those below
Decreases with altitude
Low pressure systems usually bring clouds
High pressure systems usually bring clear skies

16. Atmospheric Processes
Temperature is the relative hotness or coldness of materials
Measure of thermal energy
Water vapor content is how much water is in the gaseous form
Varies from 1% to 4%

17. Atmospheric Processes
Atmosphere moves due to
Earth’s rotation
Differential heating
Produces global patterns of prevailing winds and latitudinal belts of high and low pressure

19. What Makes the Earth Warm
Almost all the energy from the sun
Sunlight comes in a wide range of electromagnetic radiation
Long to short wavelengths
Most of the radiation that reaches the Earth is in the infrared and visible wavelengths

21. What Makes the Earth Warm
Under typical conditions Earth’s atmosphere:
Reflects ~30% of the electromagnetic energy that comes in from the sun
absorbs ~25%
The remaining ~45% gets to the surface
Radiates back to the atmosphere or into outer space

23. How We Study Climate Instrumental Records
Climate measurements began in 1860s
Data from pre 19th century is
Estimates
Extrapolated
Interpolated
We have very accurate data since 1960
Improved instrumentation

24. How We Study Climate Historical Records Paleoproxy records
Go back a few centuries
Mostly qualitative
Books, newspapers, journal articles, personal journals, ships’ logs, travelers’ diaries, and farmers’ logs
Paleoproxy records
Proxy data- not strictly climatic, but provides insight into climate
Tree rings, sediments, ice cores, fossil pollen, corals, and carbon‑14 (14C)

25. Proxy Climate Records Ice Cores
Ice cores have small bubbles of air
Can measure carbon dioxide and methane levels from the time the ice was created
Ice Cores
Polar ice and mountain glaciers have ice records that go back 100s or 1000s of years
Oldest is 800,000 years

26. Proxy Climate Records Tree Rings
Many trees create one growth ring per year
Width, density and ionic composition of the ring are indicative of climate

27. Proxy Climate Records Sediment
Biological material (ex: pollen) is deposited on the land and stored for extended periods in lake, bog, and pond sediments
Pollen is useful
Quantity of pollen is an indicator of relative abundance of each plant species
Pollen can be dated
Can be used to construct a climate history

28. Proxy Climate Record Coral Coral exoskeleton made of calcium carbonate
Carbonate contains isotopes of oxygen
Used to determine temp of water in which the coral grew

29. Proxy Climate Record
Carbon-14 and sun sunspots

30. The Green House Effect
Each gas in the atmosphere has its own absorption spectrum
Certain gases are especially strong absorbers in the infrared
They absorb radiation emitted by the warmed surfaces of the Earth
They then re-emit this radiation
This increases the temperature of the earth’s surface

32. The Green House Effect Natural phenomenon
Major greenhouse gases include
Water vapor
Carbon dioxide
Methane
Some oxides of
nitrogen
CFCs

35. Greenhouse Effect
No one doubts that the greenhouse effect exists and affects planets
The puzzle arises on the Earth about relative importance of greenhouse gases in affecting climate
Evidence indicates that carbon dioxide, methane, and temperature rise and fall together
Most scientists conclude that greenhouse gases are causing climate change

36. Positive and Negative Feedbacks
The atmosphere and its interactions w/ the ocean and land surfaces experience positive and negative feedbacks
Negative feedback
Warms temps warm air and lead to increased evaporation
Evaporation leads to more cloud formation which reflects more sunlight which could cool the surface.

37. Positive and Negative Feedbacks
Positive feedback
Warms temps warm air and lead to increased evaporation but instead of clouds forming remain as water vapor
Water vapor is a greenhouse gas. The warmer it gets the more water vapor, and the process continues

38. Causes of Climate Change
19th century
Scientists began to understand that climate changed greatly over long periods
There were times of continental glaciations
Evidence - debris at the edges of existing glaciers which looked the same as those deposited at lower elevations
Cycles were apparent
100,000 year cycles divided into 20,000– 40,000 year periods

39. Causes of Climate Change
Milankovitch Cycles
Explain why climate changes
Earth is like a wobbling top following an elliptical orbit around the sun
Three Cycles
26,000 year
Earth Does not keep its poles at a constant angle in relation to the sun
Wobble around the pole makes a complete cycle in 26,000 years

41. Causes of Climate Change
41,000 years
The tilt of wobble also varies over a period of 41,000 years
100,000 years
Elliptical orbit around the sun also changes
Sometimes it is a more extreme ellipse; other times it is closer to a circle and this occurs over 100,000 years.

43. Causes of Climate Change
The combination of these lead to periodic changes in the amount of sunlight reaching the Earth
Milankovitch showed that these variations correlated with major glacial and interglacial periods
Don’t account for all climate variations

44. Solar Cycles The Sun Goes Through Cycles
Sometimes hotter, sometimes cooler
Documented by differing amounts of isotopes trapped in glacial ice
Variability of solar input of energy explains some of the climatic variability too

45. Atmospheric Transparency Affects Climate and Weather
Transparency of atmosphere to radiation affects the temp of the Earth
From the sun coming in
From the Earth’s surface going out
Dust and aerosols absorb light
Volcanoes, forest fires and farming put dust into the atmosphere
Chemical and physical comp of atmosphere can make it warmer or cooler

46. The Ocean’s Effect on Climate Change
Water has the highest heat capacity of any compound
Large amount of heat energy is stored in oceans
Ocean absorbs dissolved CO2
As CO2 increases in atmosphere it also increases in the oceans

47. The Ocean’s Effect on Climate Change
Climate system driven (in part) by ocean conveyor belt
A global circulation of ocean waters
If the conveyor was shut down, major changes in climate would occur

48. El Niño and Climate
El Niño refers to a specific periodic variation of Pacific Ocean currents
Under non-El Niño conditions
Trade-winds blow west across the tropical Pacific
Warm surface water pile up in Western Pacific

49. El Niño and Climate During El Niño years
Trade winds weaken
Western moving current weakens or reverses
As a result eastern equatorial ocean unusually warm
High rates of precipitation and flooding in Peru
Changes global atmospheric circulation
Causes changes in weather in regions that are far removed from tropical Pacific

50. El Niño and Climate
Surface water temperature rise off the South American coast inhibits the upwelling of nutrient-rich cold water from deeper levels
Upwelling releases carbon dioxide
El Niño events reduce the amount of oceanic carbon outgassing

52. Forecasting Climate Change
Two ways to forecast the future:
Empirical and theoretical
Empirical approach is to go back to the geological idea of uniformitarianism
The past is the key to the future
Has led to the extensive research on climates and atmospheric conditions of the past

53. Predicting the Future of the Climate
Problem with Empirical approach
Temperature records are recent and not widespread
Difficult to extrapolate, interpolate and estimate
Hadley Meteorological Center in Great Britain
Reconstructing temp records

54. Predicting the Future of the Climate
Computer simulation
General Circulation Models (GCM)
Based around the atmosphere being divided into rectangular solids
Each a few km high and several km N or S
For each the flux of energy and matter is calculated to each adjacent cell
Steady state model - cannot account for randomness

56. Potential Rates of Global Climate Change
Global surface temp has increased 0.2°C/ decade in the past 30 years.
Eight warmest years have occurred since 1997
Continued warming of 0.2°C /decade is projected.

57. Potential Rates of Global Climate Change
By 2030
CO2 concentration in the atmosphere will have doubled from pre-Industrial Revolution concentrations
Average global temperature will have risen approximately 1° to 2°C
Even greater temperature increases at poles
Polar amplification

58. Potential Effects of Global Warming
Changes in River Flow
Melting of glacial ice & reductions in snow cover
Rainfall will likely increase, but runoff will be more rapid than if snow slowly melts
Reservoirs will overflow - more water will flow to the ocean

59. Potential Effects of Global Warming
Rise in Sea Level
Since last ice age, sea level has risen 1 ft/century
Global warming could double this
A major warming could increase sea levels
Expansion of liquid water as water warms
Melting of ice sheets on land whose waters then flow into the ocean
About half the people on Earth live on or near the coast - vulnerable to flooding

60. Potential Effects of Global Warming
Rise in sea level could:
Threatens island nations
Increase coastal erosion on open beaches and cause property loss.
Cause landward progression of estuaries and salt marshes
Lead to lost of coastal wetlands
Threaten ground water supply in coastal communities

61. Tuvalu, the world’s smallest nation, may succumb to sea level rise

62. Potential Effects of Global Warming
Glaciers and Antarctic Ice Cap
Far more glaciers are retreating than advancing worldwide
Northern Hemisphere sea ice coverage has declined an average of 10.7% per decade since 1970s

63. Potential Effects of Global Warming

64. Potential Effects of Global Warming
The central ice cap on Antarctica is growing
This is consistent w/ prediction of global climate change models
As Earth warms, more snow falls on Antarctica
The rate of melting of the Greenland ice sheet has doubled since 1998

66. Potential Effects of Global Warming
Changes in Biological Diversity
The Intergovernmental Panel on Climate Change (IPCC) report states that
“approximately 2–20% of species assessed so far are likely to be at increased risk of extinction as global mean temperatures exceed a warming of 2 to 3°C above preindustrial levels.”

67. Potential Effects of Global Warming
Black guillemots
Birds that nest on Cooper Island, Alaska,
The abundance of this species has decreased
Recession of sea ice occurred before chicks were mature enough to survive on their own
Parent birds feed on Arctic cod found under the sea ice
Distance from feeding grounds to nest must be <30 km
In recent years - 250km to feeding grounds
Lost an important source of food for locals

69. Potential Effects of Global Warming
Agricultural Productivity-globally
Likely to increase in some regions and decline in others
Locations most likely negatively effected
Mid-latitude food production
Lands in the southern part of the N. Hemisphere
May become more arid & soil moisture relationships will change
Human Health Effects
Difficult to forecast

70. Adjusting to Potential Global Warming
Two types
Adapt
Learn to live with future global climatic change
Mitigate
Work to reduce emissions of greenhouse gases

71. Adjusting to Potential Global Warming
How can carbon dioxide emissions be reduced?
Energy planning that relies heavily on energy conservation and efficiency
Use of alternative energy sources or natural gas
Use of mass transit
Greater economic incentives to energy- efficient technology
Higher fuel-economy

72. Adjusting to Potential Global Warming
Burning forests to convert land to agriculture
Accounts for ~20% of anthropogenic emissions of carbon dioxide
Reduce this by minimizing burning and protecting the world’s forests
Reforestation
Planting more trees
Increase biospheric sinks for carbon dioxide

73. Adjusting to Potential Global Warming
Geologic sequestration of carbon is another possible mitigation measure
Capture carbon dioxide from power plants and industrial smokestacks
Compress the gas and change it to a mixture of both liquid and gas
Inject it deep underground
Have the potential to sequester as much as 1,000 gigatons of carbon

74. International Agreements to Mitigate Global Warming
Two major approaches
International agreements in which each nation agrees to some specific limit on emissions
Carbon trading

75. Carbon Trading A nation or nation agrees to a cap of carbon emissions
Then corporations and other entities are issued emission permits, allowing a certain quantity of emissions
These can be traded
Overall nation does not exceed the cap

76. International Agreements to Mitigate Global Warming
1988
First international meeting to discuss limiting greenhouse gases held (Toronto, Canada)
1992
Earth Summit in Rio de Janeiro, Brazil.
General blueprint for reduction of global emissions suggested
US thought it would be to costly and no legally binding limits set

77. International Agreements to Mitigate Global Warming
1997
Legally binding limits discussed in Kyoto, Japan.
US eventually agreed to cut emissions to 7% below 1990 levels (leading scientists recommend cuts 60-80% below)
Became a formal treaty in 2006