Lecture Outlines Natural Disasters, 7th edition

1
Lecture OutlinesNatural Disasters, 7th edition

• Patrick L. Abbott

2
Climate ChangeNatural Disasters, 7th edition,
Chapter 12
3
Early Earth Climate An Intense Greenhouse

• Inner planets atmospheric compositions
• Venus
• Intense solar radiation, trapped by dense
  CO2-rich atmosphere ? surface temperatures 477oC
• Mars
• Less solar energy, but thin atmosphere is rich in
  CO2, so holds heat effectively, surface
  temperature -53oC
• Venus, Mars atmospheres changed little in last
  4 billion years
• Earths atmosphere radical change from CO2-rich
  to CO2-poor

4
Early Earth Climate An Intense Greenhouse
Insert Table 12.1 here.
5
Early Earth Climate An Intense Greenhouse

• Changes in Earths atmosphere caused by life
  processes
• Plants remove CO2 from atmosphere by
  photosynthesis
• Atmospheric CO2 dissolves in water, is absorbed
  by marine life
• CO2 is chemically tied up in limestone (CaCO3
  from shells, reefs, mineralized tissue of
  invertebrate animals, algae)
• Early photosynthesizing life on Earth removed
  enough CO2 from atmosphere for other animal life
  to survive ? animals made skeletons of CaCO3 ?
  further reduced atmospheric CO2 ? lessened
  greenhouse effect on Earth ? lowered temperatures

6
Early Earth Climate An Intense Greenhouse

• Changes in Earths atmosphere caused by life
  processes

Figure 12.1
7
Early Earth Climate An Intense Greenhouse

• Before life, atmosphere full of CO2, greenhouse
  effect ? surface temperature about 290oC
• Greenhouse effect
• Incoming visible light is admitted at short
  wavelengths
• Atmosphere warms up, heat is given off as
  infrared (longer wavelength) radiation
• Longer-wavelength outgoing energy is trapped
• Greenhouse effect produced by glass (in
  greenhouse, windows of car) or by gases in
  atmosphere (CO2, H2O vapor, methane (CH4),
  chlorofluorocarbons (CFCs))
• CO2 is most important greenhouse gas

8
Early Earth Climate An Intense Greenhouse

• Present CO2 is 0.038 of atmosphere ? weakened
  greenhouse effect
• Average temperature is 34oC higher than without
  CO2
• Earth has always been influenced by greenhouse
  effect
• Life has always been in dynamic equilibrium with
  greenhouse effect
• Humans now changing atmospheric CO2 concentration
• Burning tremendous volumes of living plants
  (trees and shrubs) and dead plants (coal, oil,
  natural gas)
• Relatively small amounts but may be enough to
  trigger climate shifts

9
Climate History of the Earth Timescale in
Millions of Years

• Sedimentary rocks contain information about
  climate at time they formed
• Warm climates indicated by
• Fossil reefs, limestones
• Aluminum ore bauxite (tropical soils)
• Evaporite minerals
• Cold climates indicated by
• Erosion by glaciers (distinctive marks and debris
  deposition)
• Certain fossil organisms indicate
  paleo-temperatures
• Can derive history of Earths climate

10
Climate History of the Earth Timescale in
Millions of Years

• Climate depends on balance between incoming and
  outgoing heat may be gaining or losing overall
• Earth divided into belts of frigid, temperate and
  torrid by latitude
• Ice Age
• frigid zone expands to larger area
• torrid zone shrinks but does not disappear
• Torrid Age
• torrid zone expands to larger area
• frigid zone shrinks but does not disappear

Figure 12.4
11
Climate History of the Earth Timescale in
Millions of Years

• Late Paleozoic Ice Age
• 360 260 million years ago
• Major factors (requirements for Ice Age to
  occur)
• Large landmasses near poles to accumulate
  snowfall, build continental ice sheets
• In late Paleozoic, Pangaea (supercontinent) moved
  across south polar region

12
Climate History of the Earth Timescale in
Millions of Years

• Late Paleozoic Ice Age
• 360 260 million years ago
• Major factors (requirements for Ice Age to
  occur)
• Continents blocking equatorial (east-west) ocean
  circulation
• Water must first evaporate from ocean for clouds
  to form and precipitate snow (to build ice
  sheets)
• Warm water evaporates more easily than cold water
• If continents divert warm ocean currents to flow
  north and south to the poles, more water will
  evaporate to form clouds, to drop more snow
• Ice Age may have ended because Pangaea broke apart

13
Climate History of the Earth Timescale in
Millions of Years

• Late Paleocene Torrid Age
• 65 55 million years ago
• Equatorial zones similar to today, poleward
  latitudes much warmer
• Less temperature difference between tropical and
  polar ocean waters
• Absence of cold, dense, sinking water at poles
• Less temperature difference between surface and
  deep ocean waters
• Sluggish ocean circulation
• Less temperature difference in atmosphere
• More peaceful weather, absence of strong seasons,
  evenly distributed rainfall ? warmer and wetter

14
Climate History of the Earth Timescale in
Millions of Years

• Late Paleocene Torrid Age
• Factors to create Torrid Age
• Equatorial zones were oceans, allowing more
  absorption of solar radiation by water
• As oceans warmed, snow and ice melted ? more land
  was exposed
• Land absorbs more heat than snow and ice
• Opening North Atlantic Ocean erupted huge amounts
  of lava and huge volumes of gases to atmosphere,
  increasing global warming by greenhouse effect

15
Climate History of the Earth Timescale in
Millions of Years

• Late Paleocene Torrid Age
• Factors to create Torrid Age
• Heaviest ocean water may have been dense, salty,
  oxygen-poor tropical water, as polar waters
  became warmer
• Tropical waters would have sunk to bottom,
  warming oceans from bottom up ? massive
  extinction of ocean life

• Warming of ocean water may have melted methane
  hydrates on seafloor, releasing methane gas (CH4)
  to atmosphere over 10,000 years
• Methane gas is powerful greenhouse gas, caused
  further warming

Figure 12.7
16
In Greater DepthOxygen Isotopes and Temperature

• Use ratio of stable isotopes of oxygen in CaCO3
  sea life fossils
• Oxygen may be 16O, 17O or 18O
• Evaporation removes more light 16O, leaves behind
  more heavy 18O
• Atmospheric water becomes depleted in 18O
• 18O-depleted water is trapped on land as snow or
  ice during Ice Age
• Oceans become 18O-enriched
• Marine organisms use 18O-enriched water in making
  CaCO3 shells
• Measurement of 18O/16O ratio in CaCO3 fossils is
  indicator of climate when organism lived
• High 18O/16O ? colder climate
• Low 18O/16O ? warmer climate

17
Climate History of the Earth Timescale in
Millions of Years

• Late Cenozoic Ice Age
• Long-term cooling from temperature peak at 55
  million years ago ? current Ice Age
• 55 million years ago methane reduced in
  atmosphere, began cooling
• 40 million years ago Antarctica surrounded by
  cold water
• 34 million years ago glaciers widespread in
  Antarctica
• 14 million years ago continental ice sheet on
  Antarctica, mountain glaciers in northern
  hemisphere
• 5 million years ago Antarctic ice sheet expanded
• 2.5 million years ago continental ice sheets in
  northern hemisphere

18
Climate History of the Earth Timescale in
Millions of Years

• Late Cenozoic Ice Age
• Factors in cooling
• Ongoing breakup of Pangaea
• Opening and closing of seaways ? altered ocean
  circulation and heat distribution around globe
• Continental masses in polar regions (Antarctica
  at South Pole and Eurasia near North Pole) to
  build ice sheets
• Accumulation of snow and ice at poles increased
  albedo ? more sunlight reflected

19
Climate History of the Earth Timescale in
Millions of Years

• Late Cenozoic Ice Age
• Factors in cooling
• Closing of Mediterranean and uplift of Isthmus of
  Panama stopped east-west ocean circulation,
  forcing warm water to poles
• Less area of shallow ocean ? less water surface
  to absorb sunlight
• Uplift of Tibetan plateau and Colorado plateau
  deflected west-to-east atmospheric circulation in
  midlatitudes

20
Climate History of the Earth Timescale in
Millions of Years

• The Last 3 Million Years
• Old, stable ice sheet on Antarctica little
  short-term climate effect
• North American and Eurasian ice sheets expand and
  shrink, affecting global climate
• Formation of Isthmus of Panama 3 million years
  ago blocked westward-flowing ocean water, forcing
  it north
• Warm water in north Atlantic Ocean increased
  evaporation and snowfall, to build glaciers
• Continental ice sheets in northern hemisphere
  undergo complex cycles of advance and retreat

21
Glacial Advance and Retreat Timescale in
Thousands of Years

• Last 1 million years about 10 glacial advances,
  retreats
• Worldwide glacial advances lasting almost 100,000
  years
• Followed by retreats lasting decades to few
  thousand years much faster than advance

• Caused by cycles in Earths orbit around Sun
  affecting amount of solar energy received by
  Earth
• Changes postulated in 1920s by Serbian astronomer
  Milutin Milankovitch and supported recently by
  Greenland ice cores

Figure 12.10
22
Glacial Advance and Retreat Timescale in
Thousands of Years
Milankovitch defined changes in Earths orbit,
tilt and wobble ? changes in amount of solar
radiation received by Earth

• Amount of solar radiation at high latitudes
  during summers determines how much snow remains
  from winter to next winter, allowing glaciers to
  grow

Figure 12.12
23
Glacial Advance and Retreat Timescale in
Thousands of Years

• Changes in Earths orbit
• Eccentricity of orbit around Sun varies every
  100,000 years from circular to elliptical (less
  solar radiation received when elliptical) as
  dominant control of glacial advance and retreat
• Tilt of Earths axis 21.5 24.5o off vertical
  in 41,000 year cycle
• Precession of tilt direction of tilt changes
  (wobble in spin of toy top) in double cycle of
  23,000 and 19,000 years

Figure 12.11
24
Glacial Advance and Retreat Timescale in
Thousands of Years

• Around 20,000 years ago
• Glaciers at maximum extent, covered 27 of
  todays land
• Virtually all of Canada, part of northeastern
  U.S.
• Seawater necessary to build glaciers lowered sea
  level 130 m
• Current Ice Age continues (current glacial
  retreat)
• 10 continents still buried under ice
• If ice melts, sea level would rise 65 m

25
Glacial Advance and Retreat Timescale in
Thousands of Years
Around 20,000 years ago
Figure 12.14
Figure 12.13
26
Climate Variations Timescale in Hundreds of
Years

• Temperature conditions following 20,000 years
  ago
• Warming began, then interrupted by Older Dryas
  cold stage
• Cold interval replaced by warmth of Bolling
  period
• Temperatures fell through Allerod interval and
  bottomed in Younger Dryas stage 12,900 to 11,600
  years ago
• Current interglacial period
• Temperature changes of 3o to 5oC occurred in
  several years

Figure 12.15
27
Climate Variations Timescale in Hundreds of
Years

• Cause of sudden drops or jumps in temperature
• Melting of continental ice sheets left behind
  huge cold lakes with ice dams

• Failure of ice dams released enormous amounts of
  fresh, cold water into surface layers of ocean,
  disrupting oceanic circulation pattern for 1,100
  years
• Constant rise in sea level from melting of
  glaciers

Figure 12.16
28
Climate Variations Timescale in Hundreds of
Years

• At 7,000 years ago
• Warmer global temperatures, higher rainfall
  totals ? climatic optimum
• Since then average global temperatures have
  fallen 2oC
• Smaller cycles of
• glacial expansion and
• contraction within
• cooling trend

Figure 12.17
29
Shorter-Term Climatic Changes Timescale in
Multiple Years

• El Nino
• Typical conditions in Pacific (without El Nino
  effect)
• High pressure over eastern Pacific causes trade
  winds blowing west and toward equator from north
  and south
• Westward winds push surface water to western
  Pacific
• Western Pacific water absorbs solar energy,
  evaporates easily
• Heavy rainfalls in Indonesia and southeast Asia
• Eastern Pacific has upwelling of cold, deep water
  to replace surface water blown westward

30
Shorter-Term Climatic Changes Timescale in
Multiple Years

• El Nino
• Typical conditions in Pacific (without El Nino
  effect)

Figure 12.18
31
Shorter-Term Climatic Changes Timescale in
Multiple Years

• Ocean-atmosphere coupling arrival of warm ocean
  water to Peru, Ecuador near Christmastime,
  affecting climate, every 2 to 7 years
• El Nino conditions in Pacific
• When westward blowing trade winds are absent,
  piled-up warm surface water flows downhill from
  western to eastern Pacific
• Warm surface water evaporates easily and causes
  increased rainfall to western North and South
  America
• Decreased hurricane risk to Atlantic Ocean

32
Shorter-Term Climatic Changes Timescale in
Multiple Years

• El Nino conditions in Pacific

Figure 12.19
33
Shorter-Term Climatic Changes Timescale in
Multiple Years

• El Nino 1982-83
• Cold-water fisheries off Peru and Ecuador
  collapsed
• More evaporation ? torrential rainfall, floods,
  landslides killed 600 people in Peru and Ecuador,
  economic loss
• Heavy rainstorms in western U.S. 300 million in
  damages, 10,000 people evacuated, 12 people
  killed in California
• Tropical rain belt in central Pacific formed
  hurricanes hitting Tahiti and Hawaii
• Australia and Indonesia had lower rainfall and
  droughts ? bushfires killed 75 people, 2.5
  billion in damages

34
Shorter-Term Climatic Changes Timescale in
Multiple Years

• El Nino 1997-98
• Winds flowing eastward caused heavy rains and
  floods in California
• Higher rainfall, tornadoes to southeastern U.S.
• Helped break apart Atlantic and Caribbean storms
  ? fewer hurricanes
• Warmer winter in midwestern and northern states
• More economic gains than losses, fewer fatalities
  in U.S.

35
Shorter-Term Climatic Changes Timescale in
Multiple Years

• Cause of El Nino
• Southern Oscillation in south Pacific Ocean
  usual low pressure replaced by high pressure,
  migrating from Indian Ocean (ENSO)

• Globally connected weather system
• Tropical atmosphere goes through changes that
  link up around world
• Takes four years to circuit globe

Figure 12.21
36
Shorter-Term Climatic Changes Timescale in
Multiple Years

• La Nina
• Occurs when cooler waters move into equatorial
  Pacific
• Brings cold air and high rainfall to northwestern
  U.S. and western Canada, below average rainfall
  to rest of North America
• Encourages hurricanes in Atlantic Ocean,
  wildfires in southwestern U.S.

37
Shorter-Term Climatic Changes Timescale in
Multiple Years

• Pacific Decadal Oscillation
• Lasts 20-30 years
• Midlatitude Pacific Ocean conditions, secondary
  tropical effects
• El Nino lasts 6-18 months, conditions of
  tropics, secondary effects on mid-latitudes
• Warm phase with increased storms and rainfall
• Occurred from 1925 to 1946, from 1977 to 1998

Insert Figure 12.23
Figure 12.23
38
Volcanism and Climate

• Large Plinian eruptions blast fine ash and gas to
  stratosphere, above troposphere where weather
  occurs
• Ash and sulfuric acid (from sulfur dioxide gas)
  remain in stratosphere as haze for years,
  blocking incoming sunlight

39
Volcanism and Climate

• El Chichon, 1982 Four big Plinian eruptions
• Smaller than eruption of Mount St. Helens, but
  more than 100 times SO2 gas emitted into
  stratosphere
• SO2 cloud took 23 days to circle globe ?
  spectacular sunsets
• Lowered global average temperature 0.2oC
• Followed by El Nino (may be more likely after
  major eruption)

Figure 12.24
40
Volcanism and Climate

• Mount Pinatubo, 1991
• Eruption pumped 20 million tons of SO2 into
  stratosphere
• Reflected 2-4 of incoming solar radiation ?
  20-30 decline in solar radiation reaching ground
• Average global temperatures dropped 0.5oC
• Included 1oC drop in U.S., offsetting global
  warming

Figure 12.25
41
Volcanism and Climate

• Tambora, 1815 Eruptions reduced 4,000 m volcano
  to 2,000 m high caldera, producing 175 km3 of ash
  and debris
• Made 1816 the year without a summer
• Average global temperatures lowered 0.3oC
• Triggered cholera epidemic
• Toba, Indonesia, 74,000 years ago erupted 2,000
  km3 of ash and debris
• Youngest known resurgent caldera eruption
• Ash and sulfuric acid cloud estimated to have
  lasted in stratosphere up to six years
• Global cooling possibly as much as 3-5oC ?
  volcanic winter

42
Volcanism and Climate

• Volcanic Climate Effects
• Plinian eruptions affect climate for few years,
  resurgent caldera eruptions for several years
• Possible for several different volcanoes to erupt
  over several successive years in a row (by
  chance)
• Might have long-term effects on climate ? Little
  Ice Age
• Greenland ice-core record shows high acid during
  this time
• Factors in volcanisms effect on climate
• Size, rate of eruptions
• Height of eruption columns
• Types of gases, atmospheric level of placement
• Low latitude vs. high latitude (weather patterns
  spread debris)

43
Volcanism and Climate

• Volcanic Climate Effects
• Worst-case scenario Flood basalt eruptions such
  as Deccan Plateau (India) 65 million years ago
  (extinction of dinosaurs)
• 2.6 million km3 of basaltic lava erupted in only
  500,000 years
• Possible effects
• Increase in atmospheric CO2 ? temperature
  increase of 10oC
• More acidic ocean waters
• Depleted ozone layer

44
In Greater Depth The Mayan Civilization and
Climate Change

• Great accomplishments in agriculture, irrigation,
  social organization, mathematics, astronomy over
  1,000 years
• Century-long pattern of decreased rainfall ?
  droughts ? abandonment of urban areas, stop in
  monument construction, breakdown of social and
  political order ? wars, return to life of rural
  subsistence
• Significant decline in Mayan civilization due to
  string of events triggered by long-term climate
  change

45
The Last Thousand Years

• Combined effects of eccentricity, tilt, wobble
  caused cooling trend with numerous variations
• Variations studied to learn more about
• Extent of temperature fluctations
• Whether regional or simultaneous around globe
• Causes of changes
• Other variations within cooling trend being
  studied with
• Oxygen isotopes in glacial ice layers
• Annual growth rings of corals
• Tree ring widths and densities
• Tax records of grain and grape crops
• Advances and retreats of mountain glaciers
• Paintings of frozen lakes, rivers, ports
• Weeks per year of sea ice around Iceland

46
The Last Thousand Years

• Variations within cooling trend
• Medieval Maximum warm period from 1000 to 1300
  C.E.
• Little Ice Age cold period from 1400 to 1900
  C.E. epoch of renewed but moderate glaciation
• Smaller scale coolings and warmings within Little
  Ice Age
• Maunder Minimum cooler period from 1645 to 1715
  C.E.
• Minimal sunspot activity ? Sun possibly .25
  weaker

Figure 12.28
47
The Last Thousand Years

• Processes in climate changes of last thousand
  years
• Changes in Earths orbital patterns caused
  cooling
• Lessened solar-energy production caused cooling
• Volcanism caused changes
• Interactions between ocean, atmosphere, ice
  sheets
• Millennium cycle? Warm centuries followed by cold
  centuries
• Twentieth century may have been beginning of warm
  centuries

48
Side Note Stradivari Violins

• Most famous violins increased size, secret
  varnish ? superior tones
• May have benefited from Maunder Minimum cold
  temperatures
• Longer winters and cooler summers promoted slow,
  even tree growth ? dense wood with narrow rings
• May be cause of superior tones of Stradivari
  violins

49
The 20th Century

• 20th c. began as warm as any time in past 1,000
  years
• Average global surface temperatures rose 0.6oC in
  20th century, from 1910-1944 and since 1977
• 1910-1944 warming hotter Sun, lack of volcanism
• Warming since 1977 twice that of 1910-1944
  likely mostly due to greenhouse gases in
  atmosphere
• Natural causes 0.2oC
• Changes in Earths orbital patterns ? 0.02oC
  decrease
• Hotter Sun ? more than 0.2oC increase
• Human activities 0.4oC increase

50
The Greenhouse Effect Today

• Greenhouse effect has always acted to warm Earth
  climate strength has varied
• Greenhouse gases (currently being added to
  atmosphere by humans)
• Carbon dioxide (CO2)
• Methane (CH4)
• Nitrous oxide (N2O)
• Ozone (O3)
• Industrial gases such as CFCs

51
The Greenhouse Effect Today

• The Greenhouse Effect Today
• Earths atmosphere reflects back about 30 of
  incoming solar radiation
• 23 passes through atmosphere to power hydrologic
  cycle
• Remaining 47 is absorbed by land, sea and air
• Absorbed heat builds up, some is reradiated
  outward in longer, infrared wavelengths but
  trapped by greenhouse gases in atmosphere
• Greater volume of greenhouse gases ? greater
  amount of trapped heat

52
In Greater Depth When Did Humans Begin Adding to
Greenhouse Warming?

• Burning oil, natural gas, coal, and wood
  currently releases huge amounts of CO2 to
  atmosphere
• 8,000 years ago cutting, burning forests for
  agriculture began adding CO2 to atmosphere
• 5,000 years ago wetlands technique of
  rice-growing began adding methane to atmosphere
• These agricultural practices may have warmed
  climate by as much as 0.8oC over thousands of
  years
• May have prevented some Little Ice Ages, kept
  climate stable
• Occurred over thousands of years, unlike current
  changes over decades

53
The Greenhouse Effect Today

• Carbon Dioxide (CO2)
• Causes about 60 of greenhouse warming
• Carbon cycle
• Major building block of life on Earth
• 20 of CO2 removed from atmosphere by
  photosynthesis
• At plant death, oxidation returns CO2 to
  atmosphere, into water
• Humans decompose plants at faster rates (burning
  wood and fossil fuels) ? CO2 increases in
  atmosphere and water

54
The Greenhouse Effect Today

• Carbon Dioxide (CO2)
• Carbon cycle
• 1800 CO2 concentration in atmosphere 280 ppm
• 2006 CO2 concentration in atmosphere 382 ppm
• CO2 removed from atmosphere 20 by
  photosynthesis, 25 dissolves in ocean water, but
  55 stays in atmosphere

Figure 12.32
55
The Greenhouse Effect Today

• Methane (CH4)
• Causes about 16 of greenhouse warming
• 21 times higher heat-trapping ability than CO2
• Risen more than 150 since 1750 (700 ppb)
• Released during decomposition of vegetation in
  oxygen-poor environments, by mud volcanoes
• 70 given off by human activities
• Burning fossil fuels
• Growing rice
• Maintaining livestock
• Melting of methane hydrates ? torrid climate

• Landfills
• Burning wood
• Rotting animal waste and human sewage

56
The Greenhouse Effect Today

• Nitrous Oxide (N2O)
• Produced naturally by bacteria removing nitrogen
  from organic matter, especially in soil
• Produced by humans in agricultural activities
• Chemical fertilizers
• Combustion burning of fuels in engines

• Ozone (O3)
• Ozone in stratosphere absorbs UV radiation,
  shields life
• Principal component of smog in urban atmospheres
• Produced by gases interacting with sunlight
• Irritates eyes and lungs ? shortens lives

57
The Greenhouse Effect Today

• Chlorofluorocarbons (CFCs)
• Produced solely by humans (do not occur
  naturally)
• Coolants in refrigerators and air conditioners,
  foam insulation in buildings, solvents, etc.
• Aid in destruction of ozone in stratosphere
• Remain in atmosphere for up to century (catalyst)

• Twentieth-Century Greenhouse Gas Increases
• Byproducts of industrial and domestic energy
  production, rice and livestock agriculture
• 20th century population growth (doubled twice)
• Lifestyle of industrialized world

58
The 21st Century
Intergovernmental Panel on Climate Change (IPCC)
Insert new Table 12.6 here
59
Heat Waves

• Heat is biggest killer of all severe weather
• 21st century is likely to experience more
  frequent heat waves
• Heat Wave in Chicago, July 1995
• Heat records broken, with high maximum and
  minimum temperatures (no cooling at night)
• Deaths occurred for days after 465 deaths over
  two weeks

Figure 12.35
60
Heat Waves

• Europes Heat Wave, 2003
• Summer brought record-breaking heat waves (of
  last 150 years)
• Delayed recognition of number of deaths over
  35,000
• City areas are urban heat islands, with
  night-time temperatures up to 5.5oC higher than
  surroundings
• Heat waves will occur more frequently as climate
  warms

Insert Table 12.7 here
61
Global Climate Models

• Climate change involves complex questions and
  many variables
• Questions are addressed by constructing global
  climate models (GCMs)

Insert Table 12.8 here
62
Drought and Famine

• Times of abnormal dryness in region, without
  usual rain
• Expected rains do not arrive ? vegetation begins
  to die ? food supplies shrink ? famine
• Tends to drive people apart rather than bring
  together
• Early stage food available but inadequate
• Lose up to 10 body weight, still alert and
  vigorous
• Advanced stage body weight decreases by about
  20, body reduces activity levels, apathy
• Near-death stage 30 or more body weight lost,
  indifference to surroundings and others

63
Drought and Famine

• U.S Dust Bowl, 1930s
• Several years of drought turned grain-growing
  central U.S. into dust bowl
• Position of jet stream caused upper-level,
  high-pressure dry air to sink ? hot, dry winds
  killed plants and eroded soil into dust clouds
• Drought began in 1930
• Dust storms increased in 1934, 1936
• Blame mistakenly put on farmers for plowing up
  native grasses
• May have exacerbated situation
• Droughts typical but infrequent in North America

64
Ice Melting and Sea-Level Rise

• Glacial ice holds 2.15 of water on earth
• If all melted, sea level would rise 65 m (210 ft)
• This will not happen in foreseeable future
• However, there are regions of concern
• Arctic sea ice decreased by 7.4 per decade, may
  be gone by 2030
• Possible tipping point
• Greenland continental glacier melting has
  increased, large-scale catastrophic collapses are
  possible
• Possible tipping point
• A sea level rise of 4-6 m in upcoming centuries
  would cause major problems worldwide for major
  cities and low-lying deltas

65
Oceanic Circulation

• Major climatic shift if present deep-ocean
  circulation pattern is altered by inflow of fresh
  water from melting glaciers in north Atlantic
  Ocean
• Unknown what natural changes will occur, such as
  more or less solar energy, cooling effect from
  volcanism, etc.
• Unpredictable natural changes may offset or
  accentuate human effects

Figure 12.42
66
Signs of Change
Insert revised Table 12.9 here
67
Mitigation Options

• Widely perceived need to reduce greenhouse gas
  emissions
• Will require changing energy-usage technologies
• Cap-and-trade
• Emission allowances are placed on companies
• Companies can by or sell credits
• Drastic Engineering
• Imitate volcanoes, giant shades, create clouds
  over oceans
• Efforts may create bigger problems than they solve

68
In Greater Depth Tipping Points

• Change is usually a gradual process, but not
  always
• Points at which small changes suddenly produce
  large effects
• History of change may not predict future

69
In Greater Depth Lag Times

• Changes in climate are occurring slowly
• Full effects will not be felt for decades
• IPCC estimates oceans will continue to warm
  throughout 21st century (0.6ºC)
• There are lag times in temperature changes and in
  the melting of the ice sheets

70
End of Chapter 12