1. Atmosphere Resources and Climate Change Chapter 14

2. You will learn
The nature of atmospheric resources, including the atmosphere’s composition, physical character, and role in Earth systems interactions
The nature and sources of atmosphere pollutants, including NOx, SO2, VOCs, low-level ozone, CO, and greenhouse gases, especially CO2
The effects of atmospheric pollution, including smog, acid rain, and changes in the natural stratospheric ozone layer
How variations in Earth’s orbit influence climate by changing the amount of solar radiation Earth receives

3. You will learn (cont.)
How variations in the atmosphere’s composition influence climate, what greenhouse gases are, where they come from, and how they work
How scientists study climate change
How human activities have changed the composition of the atmosphere, how these changes have altered climate and contributed to global warming, and what future challenges people will face as a result
How science is helping people understand global warming and develop ways of dealing with it, including the capture and storage of CO2

4. Composition of the Atmosphere
FIGURE Composition of the Atmosphere, Including Variable Components (by Volume)

5. Composition of Atmosphere (cont.)
Three elements (N, O, Ar)—make up over 99.9% of the atmosphere
Pure nitrogen (N2) is used in its very cold, liquid state
Instantly freezes biological specimens
Nonreactive; used to purge vessels of reactive gases like oxygen
Prevents food spoilage, and refrigerate perishables during shipping
Prevents corrosion of metal surfaces
Pure oxygen (O2)—is used in iron and steel smelting
Cutting and welding torches to achieve higher temperatures
Oxidizing agent in processes that produce a variety of chemicals
Increases the efficiency of waste incinerators
Medical applications

6. Composition of Atmosphere (cont.)
Argon (Ar)—is a colorless, odorless, nontoxic, and nonreactive gas
Creates inert environments for growing crystals—in semiconductors
Protects materials against corrosion
Fills the air space in double-pane insulating windows
The gas in incandescent and fluorescent lightbulbs.
Water vapor, methane, carbon dioxide—greenhouse gases
Keep Earth’s climate from being unbearably cold

7. The Structure of the Atmosphere
FIGURE The Structure of the Atmosphere
Temperature variations define the atmosphere’s four principal layers: the troposphere, stratosphere, mesosphere, and exosphere. The ozone layer is within the stratosphere.

8. Ozone
Ozone layer—within the stratosphere, some 15 kilometers (9 mi) up at higher latitudes and 35 kilometers (22 mi) up at low latitudes
Ozone molecules = (O3) rather than the usual two (O2).
forms when UV radiation breaks apart some O2
makes O—combines with other O2 to form O3
Ozone layer (few ppm) screens out
harmful, shortest-wavelength UV radiation
longer-wavelength UV radiation
(causes sunburn and skin cancer)

9. The Atmosphere Screens Earth from Harmful Solar Radiation
FIGURE The Atmosphere Screens Earth from Harmful Solar Radiation
Shorter wavelength gamma and X-ray radiation and large amounts of infrared radiation are completely absorbed by the atmosphere. The ozone layer absorbs the most harmful ultraviolet wavelengths. Only radio waves, visible light, and some ultraviolet radiation reach Earth’s surface relatively unimpeded.

10. Air Pollution The EPA considers common air pollutants to be:
Volatile organic compounds (vocs)
Nitrogen oxides (NO and NO2)
Sulfur dioxide (SO2)
Carbon monoxide (CO)

11. Air Pollution (cont.) Common greenhouse gases are:
Water vapor (H2O), methane (CH4), CO, nitrous oxide (N2O)
Volatile organic compounds—(VOCs)
Chemicals that contain carbon and hydrogen and vaporize easily
Benzene, toluene, butane, and propane are examples
Paint thinners, solvents, plastics, and gasoline
VOCs evaporate from crude oil when exposed to atmosphere
In the presence of sunlight—chemical reactions that lead to smog

12. NOx and SO2 Nitrogen oxides—NOx
Family of nitrogen-oxygen compounds where N:O ratio varies
Nitrogen oxide (NO) and nitrogen dioxide (NO2)
Nitrous oxide (N2O) is not toxic like NO and NO2—effective greenhouse gas
Produced during combustion of fossil fuels
Key ingredient in the formation of smog, contributes to developing acid rain, and causes respiratory problems for people

13. NOx and SO2 (cont.) Sulfur dioxide
Oil and coal combust and S combines with O = sulfur dioxide (SO2)
In the atmosphere, SO2 + H2O + O = sulfuric acid (H2SO4)
Source of acid rain
Causes respiratory problems for people
Reacts with nitrogen in the atmosphere to form ammonium sulfate
Creates atmosphere haze
Volcanic eruptions may release SO2 into the atmosphere
Special effect—global cooling

14. Emissions FIGURE 14-5 Emission Trends
Regulations developed by the EPA have had a major influence on pollutant emissions in the United States. A a result, air pollution levels are near or significantly below national standards and the trends continue downward.
FIGURE Sources of SO2 Pollution in the Atmosphere
Although SO2 emissions in the United States have significantly decreased, over 10 million tonnes (11 million tons) are released into the atmosphere each year.

15. CO and CO2 Carbon monoxide—CO
Colorless, odorless, tasteless, and dangerous gas
75% of CO—produced by incomplete combustion of fossil fuels
CO is a good general indicator of air pollution
Can be detected and mapped by satellite-borne instruments
EPA vehicle regulations—effective at lowering levels of CO

16. CO and CO2 (cont.) Carbon dioxide—CO2
Source of CO2 emissions—burning fossil fuel with CO2 as product
Metabolism of food—source of CO2 that we exhale
Volcanic eruptions may release large amounts of CO2
The Supreme Court—greenhouse gases are atmospheric pollutants
EPA can regulate under the clean air act
This ruling signals changes for CO2 emitters
Example—EPA permits for new coal-fired power plants must now consider a “best available control technology” for CO2 emissions—as for other air pollutants

17. Smog Combination of smoke and fog
Originally referred to the haze from extensive burning of coal
CO, NOx, and VOC emissions cause most of today’s smog problems
FIGURE Two of the Reactions Involved in Forming Ozone (O3) and Smog There are several other reactions involving NOx, VOCs, CO, and O (in the presence of sunlight) that also contribute to ozone and smog formation.

18. Photochemical Smog and Acid Rain
Photochemical smog—brownish haze over cities on warm, sunny days
Brownish color comes from Nox, smell comes from ozone
Most dangerous component is low-level ozone
Irritates lungs—damages vegetation
Cause—photochemical reactions involving VOCs, NOx, and CO
Solution—more efficient combustion of fossil fuels
Reformulating gasoline
Catalytic converters, electronic engine controls, exhaust gas recirculators

19. Photochemical Smog and Acid Rain (cont.)
NOx and SO2 react with water (atmosphere) to form droplets of acid
SO2 emissions = principal cause of acid rain
Coal-burning power plants—release 70% of SO2 emitted each year
Acid rain has a ph less than 5.6; NE U.S.—rain can have ph = 3.6 !!
Acid rain in NE has affected vegetation, aquatic systems, buildings—damaging plant leaves, degrading soil, dissolving nutrients

20. Formation of Acid Rain FIGURE 14-11
Both NOx and SO2 can react with water in the atmosphere to form droplets of acid, but SO2 emissions have been the principal cause of acid rain

21. Acid Rain in the NE U.S.
Where acid rain accumulates in surface waters, acidity can reach levels that are unhealthful for fish and other aquatic life. Some lakes in the northeast U.S. have pH levels <5. Acid rain falls on limestone and marble (buildings, tombstones, etc.) and dissolves bits of the building stone and pits, etches, and discolors the building surfaces. In places, structural components are weakened and need to be replaced.
FIGURE Acid Rain and Power Plant Emissions (a) The location of coal-burning power plants. (b) The acidity of rainwater in different parts of the United States. The distribution of plants combined with prevailing winds (from west to east) make acid rain common in the east and northeast parts of the country.

22. The Ozone Layer
The ozone layer in the stratosphere absorbs shorter-wavelength UV radiation in sunlight that would otherwise be lethal to surface life
Photosynthesis releases oxygen
Migrates to high altitudes—reacts with UV radiation to form ozone
Ozone layer effectively shields surface life
Is carried to higher latitudes by stratospheric winds
Chlorofluorocarbons (CFCs)—destroy ozone
UV radiation breaks cfcs down in stratosphere
Releasing Cl and Br atoms that react with ozone
Cl and Br atoms—very effective at destroying ozone
Seasonal depletion over Antarctica is known as the ozone hole
The ozone hole—well developed between August and late November

23. How Chlorine Destroys Ozone
FIGURE How Chlorine Destroys Ozone
CFCs have such a devastating effect on ozone because the reactions involved form a cycle. Once a single chlorine atom is dislodged from a CFC molecule, it can just keep reacting with one ozone molecule after another.

24. Atmosphere and Climate Change
Earth’s climate is strongly influenced (forced) by:
1) atmosphere composition; 2) solar radiation Earth receives
Composition—greenhouse gases
Let shorter-wavelength incoming sunlight through to Earth’s surface
Warm the ground, the ocean, and lower regions of the atmosphere
Reradiate some of their heat energy back at longer wavelengths
Infrared wavelengths are absorbed by greenhouse gases
Trapping energy in the atmosphere
Part of this trapped energy is, in turn, reradiated back to Earth

25. Atmosphere and Climate Change (cont.)
This trapping of heat in the atmosphere is often likened to the effect of glass in a greenhouse—hence the term greenhouse effect
This greenhouse effect keeps Earth’s surface habitable
CO2—low warming potential—very abundant, hence important
Methane—56x warming potential of CO2—not abundant
Nitrous oxide—280 warming potential of CO2—not abundant
Water vapor too is a very potent greenhouse gas—temperature-dependent

26. The Greenhouse Effect FIGURE 14-18 The Greenhouse Effect
Solar radiation reflected or reradiated by Earth’s surface is absorbed by greenhouse gases and warms the atmosphere. The warmed atmosphere reemits radiation back to Earth, causing surface warming.

27. How Axis Tilt Affects the Intensity of Solar Radiation
FIGURE It is because the axis is tilted that we have seasons.
(a) The tilt of Earth’s axis of rotation changes from 22.1 to 24.5 degrees and back in a 41,000-year cycle.
At higher latitudes, even the shift of a few degrees can cause a significant change in the intensity of solar radiation.
(b) Solar radiation reaching Earth’s surface is strongest when the Sun is directly overhead and becomes weaker when Sun's rays strike at a more oblique angle.

28. How Axis Tilt Affects the Intensity of Solar Radiation (cont.)
FIGURE How Axis Tilt Affects the Intensity of Solar Radiation
In (c), the Northern Hemisphere is tilted toward the Sun and experiences summer while the Southern Hemisphere experiences winter. Six months later, when Earth is on the opposite side of its orbit (d), the Northern Hemisphere is tilted away from the Sun and experiences winter while the Southern Hemisphere experiences summer.

29. Influence of Orbital Eccentricity
FIGURE 14-20
How Orbital Eccentricity Changes the Amount of Solar Radiation Earth Receives
Earth’s orbit around the Sun changes from more elliptical (a) to less elliptical (b)
and back about every 100,000 years.
(The extent of the elongation in part (a) has been exaggerated.) When the orbit is more elliptical, the Earth moves both closer to and farther from the Sun during a year than it does when the orbit is less elliptical.

30. Precession
FIGURE Precession
Earth wobbles as it orbits the Sun, much as a top wobbles as it spins. This wobble gradually rotates the poles in a circle. Precession changes the direction of Earth’s tilt about its axis, but not the amount of tilt. Rotation of the poles shifts them slightly toward or away from the Sun. A complete precession cycle takes 22,000 years.
Milankovitch Cycles—cyclic changes in axis tilt, orbital eccentricity, and precession cycles lead to cycles of colder climate (glacial maximums) and warmer climate (interglacial periods)

31. Tectonic Processes and Climate
Continent size and distribution
The size and distribution of these landmasses directly affect circulation patterns
Affect the concentration of CO2 in the atmosphere
Influence on the chemical weathering of silicate minerals
Atmosphere transfers dissolved CO2 to the geosphere through rain
Reacts with water to give carbonic acid (H2CO3)
Chemical-weathering processes break down silicate minerals
Reactions work to decrease atmospheric CO2 concentrations
Silicate weathering is likely to be more extensive:
Continents split into smaller fragments surrounded by oceans—wetter
Continentals are located at lower latitudes—warmer conditions

32. Tectonic Processes and Climate (cont.)
Mountain ranges
Direct influences on atmosphere circulation and precipitation
Increase exposure of silicate minerals to chemical weathering
Decrease CO2 concentrations in the atmosphere
Volcanoes
Volcanic gases (e.g., SO2) reach high altitudes—cool Earth
May release enough CO2 to affect global climate for long periods of time.

33. Average Past Global Temperatures
FIGURE Average Global Temperature during the Phanerozoic
Over the last 540 million years, Earth was mostly warmer than it is now.
Earth’s geologic record shows evidence of past climates both colder and warmer than today. These past climates are related to interactions involving geosphere processes, greenhouse gas cycles, the distribution and size of continents and oceans, and variations in the amount of solar radiation Earth receives.

34. Paleoclimatology—Studying Past Climates
Sedimentary records
Evaporites (salt-rich sediments) indicate arid conditions
Coal seams commonly indicate warm, moist conditions
Tillite indicates cold, glacial conditions
Cores of deep-sea sediments with continental rock debris (from icebergs)
Fossils
Remains of organisms help determine environmental conditions
Zooplankton and algae—indicators of water temperatures
Fossil plant spores and pollen

35. Paleoclimatology—Studying Past Climates (cont.)
Oxygen isotopes
Almost all oxygen has an atomic mass of 16 (16O, or O-16 atoms)
Two other stable oxygen isotopes are: O-17 and O-18.
O-18 is five times more abundant than O-17—easier to use
O-18 is slightly heavier than O-16
Water containing O-18 does not evaporate as easily as water with O-16
The escaping water vapor is slightly enriched in O-16
Seawater left behind is slightly enriched in O-18
During cold periods
O-16-enriched water vapor is added to ice sheets
Ratio of O-18 to O-16 in seawater increases
Marine organism incorporate this O-18 : O-16 into shells and skeletons
Locking in ratio for time they grew
Expanding ice sheets—higher O-18 to O-16 ratios
Contracting ice sheets—decreasing O-18 to O-16 ratios

36. Oxygen-16 in Glacial Ice FIGURE 14-25
How Oxygen-16 Becomes More Concentrated in Glacial Ice
(a) Because O-16 is lighter than O-18, water vapor evaporated from the oceans is slightly enriched in O-16.
Because most of this water eventually finds its way back to the oceans in rain and runoff, however, the ratio of the two isotopes in seawater is largely unaffected.
(b) During times of glaciation, water vapor enriched in O-16 becomes trapped in ice accumulations and doesn’t return to the oceans. As a result, the relative concentration of O-18 in seawater increases.

37. The Phanerozoic Oxygen Isotope Record of Seawater
FIGURE The Phanerozoic Oxygen Isotope Record of Seawater
The variation in the ratio of O-18 to O-16 is determined from measurements of oxygen isotopes in fossil marine shells and skeletons. A greater O-18 to O-16 ratio indicates colder periods.

38. Paleoclimatology—Studying Past Climates (cont.)
Atmosphere samples in ice cores
Air is trapped in snow each year on ice sheets
Snow becomes compressed under the weight of new snow and turns into ice
Enclosed air becomes trapped in the ice as bubbles of ancient air
Bubbles can be analyzed for their content of greenhouse gases
Determine prehistoric atmospheric concentrations of methane and CO2

39. Paleoclimatology—Studying Past Climates (cont.)
Sea level history
Shifts from cold to warm climate marked a change from expanding permanent ice sheets to melting ice sheets.
Major cold periods make major continental-scale ice sheets
Trap tremendous volumes of water evaporated from the oceans
Lower sea level
Warm periods melt the great ice sheets
Send tremendous amounts of water back to the oceans
Sea level rises

40. Atmospheric Gases Trapped in Ice at Vostok Station, Antarctica
FIGURE Atmospheric Gases Trapped in Ice at Vostok Station, Antarctica
Higher concentrations of methane (a) and carbon dioxide (b) in air bubbles trapped in ice cores indicate warmer interglacial times. Earth entered a warming interglacial period 20,000 years ago.

41. Shifts between Warm and Cold Periods during Last 3 Million Years
FIGURE 14-30
Shifts between Warm and Cold Periods during the Last 3 Million Years
The plots are based on deep-sea sediment oxygen isotope data. Up to 0.9 million years ago, shifts from warm to cold climates occurred every 41,000 years (the axis tilt cycle). Since then the shifts have been every 100,000 years.

42. The Last 10,000 Years of Greenhouse Gas Concentrations
FIGURE The Last 10,000 Years of Greenhouse Gas Concentrations
The curves represent the concentrations of atmospheric CO2 (a) and methane (CH4) (b) as determined from ice cores.
Note the shift from the longer-term natural trends at about 7000 years ago for CO2 and at 5000 years ago for methane. Could this be related to an increase in farming practices?
If data for the last 200 years were included, the CO2 concentration would go off the chart—CO2 concentrations increased to 380 ppm during this time!

43. Climate Models—IPCC
A scientific model is a physical or mathematical representation of system relationships and processes
General Circulation Models, GCMs, represent the interactions of the major components of climate system: solar radiation, atmosphere, oceans, land, and ice

44. Climate Models—IPCC (cont.)
GCMs share characteristics of all models, including:
They are incomplete. Models represent what scientists consider to be the most important components: ocean temperature, solar radiation levels, atmosphere and ocean circulation patterns, and greenhouse gas concentrations, for example
They require assumptions. Scientists must assume many quantitative aspects of the climate system components and their relationships to one another—for example, the rate at which CO2 is being added to the atmosphere each year. They base such assumptions on what they can reasonably project from past experience and on the best existing information
They incorporate variable parameters. The components of the climate system vary in their physical character through space and time; for example, ocean water temperatures vary around the world

45. Climate Models—Feedback Loops
Sophisticated models take changes into consideration as they simulate future conditions. Feedback mechanisms respond to a change in the climate system and either amplify or diminish the change.
positive feedbacks—amplify the change
negative feedbacks—diminish the change
Increasing ocean temperatures decrease the amount of CO2 oceans can absorb. This in turn increases atmospheric CO2 concentrations and their greenhouse gas effect causes additional ocean temperature warming. This is an example of a positive feedback.

46. Climate Models—Feedback Loops (cont.)
With climate warming, ice sheets melt and reflect less solar radiation. This in turn causes more surface warming, a positive feedback
Increasing air temperatures enable more water vapor to be stored in the atmosphere. As water vapor has a significant greenhouse gas effect, more water vapor increases surface and air temperatures, a positive feedback.
If increased air temperatures lead to increased water vapor in the atmosphere, an outcome can be increased cloudiness. Clouds reflect incoming solar radiation and decrease surface and air temperatures, negative feedback

47. FIGURE 14-35 Atmospheric CO2 Concentrations Increased Very Rapidly during the Last 200 Years
The change from about 280 ppm in 1800 to 380 ppm today reflects the impact of the Industrial Revolution and the increased use of fossil fuels.

48. FIGURE 14-37 The Global Climate System Is Very Complex
This figure shows some of the many interlocking feedback mechanisms that affect global climate. (You don’t need to worry about the details—the purpose of the figure is just to suggest why the system is so challenging to model.)

49. IPCC Story Lines and Scenarios
Define the scope of possible changes the world may experience by 2100:
A1—very rapid economic growth, low population growth, and the rapid introduction of new and more efficient technologies. Themes are convergence among regions, capacity building, and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.
A2—very heterogeneous world. Theme is self-reliance and preservation of local identities. High population growth. Economic development is regionally oriented, and per capita economic growth and technological change are more fragmented and slower than in other story lines.
B1—convergent world with the low population growth (like A1), but with rapid changes toward a service and information economy, with reductions in material intensity, and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social, and environmental sustainability, including improved equity, but without additional climate initiatives.
B2—emphasis is on local solutions to economic, social, and environmental sustainability. Moderate population growth, intermediate levels of economic development, and less rapid and more diverse technological change.

50. FIGURE 14-36 Average Global Temperature Rise over the Past Century
Instrument-measured air temperatures are compared to the average from 1961 to 1990 (the zero line) to calculate the observed temperature anomaly.

51. The IPCC 2007 Assessment
Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.
Global GHG (greenhouse gas) emissions due to human activities have grown since preindustrial times.
Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.
It is likely that there has been significant warming caused by human activities over the past 50 years averaged over each continent (except Antarctica).

52. The IPCC 2007 Assessment (cont.)
There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global GHG emissions will continue to grow over the next few decades.
Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century—would very likely be larger than those observed during the 20th century.
A wide array of adaptation options are available, but more extensive adaptation than is occurring is required to reduce vulnerability to climate change.

53. FIGURE Examples of Impacts Associated with Different Amounts of Global Average Temperature Change Projected here by the IPCC.

54. Kyoto Protocol and Carbon Sequestration
The Kyoto Protocol
Identified CO2 emission reduction goals for all participating countries.
As of May 2008, 181 countries are parties to the agreement
Developing countries are not required to limit their emissions
Countries with a lot of CO2 emissions are not participating
Carbon sequestration

55. Kyoto Protocol and Carbon Sequestration 9 (cont.)
Capturing and storing CO2 emitted by hydrocarbon burning
Physical membranes that separate CO2 from exhaust streams
Use of sorbents that chemically react with emitted CO2
A bigger challenge is storing CO2 after it’s captured.
Reacting CO2 with Ca, Mg, Fe to form stable carbonate minerals
Storage in underground geologic reservoirs—geosequestration
Injects captured CO2 into permeable reservoirs
Depleted oil fields, saline water-filled formations
Overlain by impermeable layers to trap CO2 and prevent leaking
Making of methanol (wood alcohol, CH3OH)

56. FIGURE 14-43 An Example of Carbon Capture Technology
CO2 emissions from a large point source first combine with solid sodium carbonate in the carbonation reactor. The resulting sodium bicarbonate is heated in the decarbonation reactor. This releases concentrated CO2 and regenerates sodium carbonate that is recycled back to the carbonation reactor.

57. SUMMARY
The atmosphere supports life and supplies useful elements (e.g., O, N, Ar).
The atmosphere absorbs gamma rays, X-rays, and ultraviolet radiation.
Atmospheric pollutants include NOx, SO2, VOCs, low-level ozone, CO, CO2.
Greenhouse gases include CO2, methane, water vapor, and N2O.
Smog = reactions with VOCs and NOx that produce low-level ozone.
Acid rain forms from reactions between NOx and SO2 and H2O vapor.
Stable Cl- and BR-bearing compounds, CFCs, are emitted to the atmosphere.

58. SUMMARY (cont.)
Greenhouse gases in Earth’s atmosphere absorb heat radiated by Earth, trap it in the atmosphere, and reradiate it back to Earth, causing surface and ocean temperature increases.
Variations in solar radiation caused by cyclic changing of the tilt of Earth’s axis, Earth’s distance from the Sun due to orbital eccentricity, and Earth’s wobble as it orbits the Sun are significant controls on global climate.
Shifts between warm and cold climates have occurred for large parts of Earth’s history (e.g., 40–50 cycles during the last 2 to 3 million years)
The last glacial maximum occurred 20,000 years ago—incoming solar radiation increased between 20,000 and 10,000 years ago, the ice sheets melted, and sea level rose some 110 to 125 meters (360 to 410 ft).
Addition of greenhouse gases has led to global warming.