An introduction to global climate change

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An introduction to global climate change

• On August 29, 2005, Hurricane Katrina landed east
  of New Orleans
• The costliest (134 billion in damage) storm ever
• The deadliest storm (killing 1,800) since 1928
• Leaving mountains of debris, ruined homes and
  lives
• A month later, Hurricane Rita hit Louisiana and
  Texas
• 2005 had a record 27 named storms
• 2007 had 15 and 2008 had 18 named storms
• There is a link between hurricanes and global
  warming
• Warmer oceans create humid air, leading to
  hurricanes

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Number of category 4 and 5 hurricanes
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Structure and temperature of the atmosphere
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Weather

• Weather day-to-day variations in temperature,
  air pressure, wind, humidity, precipitation
• Climate the result of long-term regional weather
  patterns
• Meteorology the study of the atmosphere (weather
  and climate)
• The atmosphere-ocean-land system is a huge
  weather engine
• Driven by the Sun and affected by Earths
  rotation and tilt
• Solar energy is reflected (29) or absorbed by
  Earth
• Absorbed energy heats the ocean, land, and
  atmosphere

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Solar-energy balance
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Climate is

• Climate the general patterns of weather that
  characterize different regions of the world
• Climate results from all the combined elements of
• General atmospheric circulation patterns and
  precipitation
• Wind and weather systems
• Rotation and tilt of Earth, which creates seasons

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Synopsis of global climate change

• In 2007, scientists from the Intergovernmental
  Panel on Climate Change (IPCC) sifted through
  thousands of studies and published the Fourth
  Assessment Report (AR4)
• The report concluded that warming of the climate
  is unequivocal
• The atmosphere and oceans are warmer
• Sea levels are rising and glaciers are melting
• There are more extreme weather events

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Annual mean global surface temperature anomalies
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The IPCCs report

• The report concluded that it is very likely (90
  probability) that warming is caused by human
  factors
• Increased greenhouse gases (GHGs) trap infrared
  radiation
• GHGs come from burning fossil fuels
• Along with deforestation
• The major GHG CO2
• Responses to climate change
• Mitigation reducing GHG emissions
• Adaptation adjusting to climate change

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Atmospheric carbon dioxide concentrations
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IPCC

• Founded in 1988 by the UN Environmental Program
  and the World Meteorological Society to provide
  accurate and relevant information leading to
  understanding human-induced climate change
• The AR4 report had over 2,000 experts from 154
  countries
• Risk assessment is the climate changing?
• Risk management how do we adapt and mitigate
  effects?

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Third assessment

• The IPCCs 2001 report showed
• Increasing information shows a warming world
• Humans are changing the atmosphere, which will
  affect climate
• We have increased confidence in models of future
  climate change
• Stronger evidence that most recent warming is
  human-caused
• Human influences will continue to change the
  atmosphere
• Temperature and sea levels are rising
• We need more information and understanding

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A Nobel Effort

• The 2007 Nobel Peace Prize went to the IPCC and
  former Vice President Al Gore the leading
  advocate of the need to take action on climate
  change
• For their efforts to disseminate knowledge about
  man-made climate change and to lay groundwork to
  counter it
• Gore also was awarded the Academy Award for his
  film An Inconvenient Truth

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Climates in the past

• It is harder to find evidence of climate change
  the further into the past we search
• Records of temperature, precipitation, storms
  have been kept for only 100 years
• Since 1880, especially since 1976, our climate
  warmed
• Proxies records providing information on climate
• Using temperature, ice cover, precipitation, tree
  rings, pollen, landscapes, marine sediments,
  corals, etc.
• Earth warmed from 1100 to 1300 A.D.
• Little Ice Age 14001850

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Ice cores

• Analyzing ice cores from Greenland and the
  Antarctic shows global climate can change within
  decades
• Uses CO2 and CH4 (methane) and isotopes of O and
  H
• Climate oscillates between ice ages and warm
  periods
• Ice ages tie up water in glaciers, lowering sea
  levels
• 8 glacial periods occurred over the past 800,000
  years
• Ice ages have lower GHGs and temperatures
• CO2 levels ranged between 150 and 280 ppm
• Milanovitch cycles climate oscillations due to
  Earths orbit
• Periodic intervals of 100,000, 41,000, and 23,000
  years

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Rapid changes

• Rapid climatic fluctuations during glaciation and
  warmer times
• The Younger Dryas event 11,700 years ago
• Dryas a genus of arctic flower
• Arctic temperatures rose 7ºC in 50 years
• Caused enormous impact on living systems
• Warming was not caused by changing solar output

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Oceans and climate

• Oceans play a dominant role in determining
  climate
• They are a major source of water and heat
• Evaporation supplies water vapor to the
  atmosphere
• Condensation supplies heat to the atmosphere
• Heat capacity oceans absorb energy with heated
  water
• Oceans convey heat through currents
• Thermohaline circulation pattern the effects of
  temperature and salinity on the density of
  seawater
• This giant, complex conveyor belt moves water
  from the surface to deep oceans and back

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The oceanic conveyor system
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Thermohaline circulation affects climate

• The movement of warm water toward the North
  Atlantic transfers enormous amounts of heat
  toward Europe, providing a much warmer than
  expected climate
• The circulation pattern cycles over 1,000 years
• It is vital to maintaining current climate
  conditions
• In the past, the conveyor system has been
  interrupted
• Abruptly changing the climate
• Large amounts of fresh water lower waters
  density
• Preventing the sinking of surface waters
• Slowing the northern movement of warmer, saltier
  water

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Heinrich events

• Heinrich events fresh water from melting
  icebergs from the polar ice cap dilutes salt
  water
• Six times in the past 75,000 years
• Diluted water doesnt sink
• The conveyor system is shifted southward to
  Bermuda (instead of Greenland)
• The climate cools in a few decades
• Return of the normal pattern abruptly warms the
  climate
• The Younger Dryas event involved dammed-up water
  from glacial Lake Agassiz entering the St.
  Lawrence

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What if ?

• Extended global warming will
• Increase precipitation over the North Atlantic
• Melt sea ice and ice caps
• The conveyor will decrease over the 21st century
• The Achilles heel of our climate system
  weakening of the conveyor and a changed climate
• Especially in the northern latitudes

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The Earth as a greenhouse

• Factors that influence climate
• Internal components oceans, atmosphere, snow,
  ice
• External factors solar radiation, Earths
  rotation and orbit, gaseous makeup of the
  atmosphere
• Radiative forcing the influence of any factor on
  the energy balance of the atmosphere-ocean-land
  system
• Positive (negative) forcing leads to warming
  (cooling)
• Forcing is measured in Watts/m2
• Solar radiation entering the atmosphere 340
  W/m2
• Radiation is acted on by forcing factors

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Warming processes

• Greenhouse gases (GHGs) water vapor, CO2, other
  gases
• Light energy goes through the atmosphere to Earth
• Earth absorbs and converts energy to heat
• Infrared heat energy radiates back to space
• GHGs (but not N2 and O2) in the troposphere
  absorb some infrared radiation
• Direct it back to Earths surface
• The greenhouse effect was first recognized in
  1827
• It is now firmly established

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GHGs insulate Earth

• GHGs delay the loss of infrared heat (energy)
• Without insulation, Earth would be -19C instead
  of 14C
• Life would be impossible
• Earths global climate depends on the
  concentration of GHGs
• Changing amounts of GHGs change positive forcing
  agents, which would change the climate
• Tropospheric ozone has a positive forcing effect
• Varying with time and location

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The greenhouse effect
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Cooling processes

• Planetary albedo sunlight reflected by clouds
• Contributes to overall cooling by preventing
  warming
• Low-flying clouds have a negative forcing effect
• High-flying, wispy clouds have a positive forcing
  effect
• Absorb solar radiation and emit infrared
  radiation
• Snow and ice contribute to albedo by reflecting
  sunlight

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Volcanoes and aerosols

• Volcanic activity can lead to planetary cooling
• Reflects radiation from particles and aerosols
• Aerosols microscopic liquid or solid particles
  from land or water
• Industrial aerosols (pollution) cancel some GHG
  warming
• Sulfates, nitrates, dust, soot from industry and
  forest fires
• Sooty aerosols (from fires) warming effect
• Reduced pollution in the U.S. and Europe
  decreased aerosols
• Chinas and Indias pollution has increased
  aerosols

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Global warming and cooling
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Solar variability

• Variation in the Suns radiation influences the
  climate
• Changes in solar radiation occur on 11-year
  cycles
• Solar radiation increases during high sunspot
  activity
• Sunspots block cosmic ray intensity
• Solar output declined in 1985 and continued for
  20 years
• But global temperatures rose rapidly
• The IPCC AR4 concluded that GHGs were 13 times
  more responsible for warming temperatures than
  solar changes

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Thus

• Global atmospheric temperatures are a balance
  between positive and negative forcing from
  natural causes (volcanoes, clouds, natural GHGs,
  solar irradiance) and forcing from anthropogenic
  causes (sulfate aerosols, soot, ozone, increased
  GHGs)
• Forcing agents result in climate fluctuations
• It is hard to say any one event or extreme season
  is due to humans
• But climate has shifted enough to generate
  international attention

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Evidence of climate change

• Weather varies naturally year to year
• Local temperatures may not follow global averages
• But the 10 warmest years on record were 19972008
• 2005 set a record highthe warmest since the late
  1800s
• The average global temperature has risen 0.6C
  since the mid-1970s (0.2C/decade)
• Warming is happening everywhere
• Most rapidly at high latitudes of the Northern
  Hemisphere
• The warming is a consequence of an enhanced
  greenhouse effect

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Ocean warming

• Recently, the upper 3,000 meters of the ocean
  have warmed
• Dwarfing warming of the atmosphere
• 90 of the heat increase of Earths systems
• Over the last decade, oceans have absorbed most
  of the non-atmospheric heat
• A long-term consequence the impact of this
  stored heat as it comes into equilibrium with the
  atmosphere
• It will increase atmospheric and land heat even
  more
• A short-term consequence unprecedented rising
  sea levels
• Thermal expansion and melting glaciers and ice
  caps

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The rise in global mean sea level
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Other observed changes by the IPCC AR4

• Changes are consistent with GHG-caused climate
  change
• Increased warm temperature extremes
• Decreased cold temperature extremes
• Spring comes earlier, fall later, in the Northern
  Hemisphere
• Ecosystems are out of sync
• Tree deaths and insect damage
• Heat waves are increasing in intensity and
  frequency
• Droughts are increasing in intensity and
  frequency
• 60 of the U.S. is in a drought that started in
  the 1990s

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More changes reported by the IPCC

• Rising Arctic temperatures have caused major
  shrinkage of Arctic sea ice (11.7 in 10 years)
• Alaska, Siberia, Canada have warmed 5F in
  summer, 10F in winter
• Spring comes 2 weeks earlier than 10 years ago
• The polar ice cap has lost 20 of its volume in
  20 years
• Permafrost is melting
• Unprecedented melting of the Greenland Ice Sheet
  can raise ocean levels 23 feet

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Decline of Arctic sea ice
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Other changes reported by the IPCC

• Antarctica temperatures have risen 0.50.85C
• The West Antarctic Ice Sheet (WAIS) is shrinking
  and can raise sea levels by 1620 feet
• Accelerating glacier melting since 1990
• Changing patterns of precipitation and flooding
• Greater amounts from 30 N and S poleward
• More intense and frequent tropical hurricanes
• Marine fish populations have shifted northward
• Ocean acidification decreased pH due to CO2
  absorption
• The surface oceans chemistry is actually changing

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Carbon dioxide levels

• CO2 levels oscillate 57 ppm, reflecting
  seasonal changes in photosynthesis and
  respiration
• Fall through spring respiration increases CO2
  levels
• Spring through fall photosynthesis decreases CO2
• By 2009, atmospheric CO2 levels 338 ppm
• 39 higher than before the Industrial Revolution
• Higher than in the past 800,000 years
• Fossil fuels increase CO2 levels
• 1 kg of fossil fuel burned releases 3 kg CO2
• Eight billion tons (gigatons, Gt) of fossil fuel
  carbon/year

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Sources of carbon dioxide

• Half of fossil fuel carbon comes from
  industrialized nations
• Burning forests
• Over the past 50 years, release of carbon has
  tripled
• Half of the carbon is removed by sinks
• Sinks burning fossil fuels should add 8 GtC/year
  to the air
• But only 3.3 GtC/year are actually added
• Carbon sinks (the ocean, biota) absorb CO2
• Oceans take up CO2 by phytoplankton or
  undersaturation
• But there are limitations to uptake
• Forests are valuable for their ability to
  sequester carbon

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Sources of carbon dioxide emissions from fossil
fuels
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Other gases

• Other gases absorb infrared radiation
• Adding to the insulating effect of carbon dioxide
• Most are anthropogenic sources and are increasing
• Water vapor the most abundant GHG
• Its tropospheric concentration varies, but is
  rising
• Higher temperatures increase evaporation and
  water vapor (humidity)
• Higher humidity traps more heat, causing more
  warming (positive feedback)

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Other GHGs

• Methane 20 times more effective than CO2 in
  heating
• From microbial fermentation (in wetlands), green
  plants
• Two-thirds of emissions are from human sources
  livestock, landfills, coal mines, natural gas,
  rice cultivation, manure
• Rising at 0.8 ppb/year, it is more abundant than
  in the past 800,000 years
• Nitrous oxide has increased 18 over the last
  200 years
• From agriculture, oceans, biomass burning, fossil
  fuel burning, industry, anaerobic denitrification
  (fertilizers)
• Warms the troposphere and destroys stratospheric
  ozone

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Ozone and CFCs

• Ozone a short-lived but potent GHG in the
  troposphere
• From sunlight acting on pollutants
• Has increased 36 since 1750
• From traffic, forest fires, agricultural wastes
• CFC and other halocarbons
• Long-lived GHGs causing warming and ozone
  destruction
• From refrigerants, solvents, fire retardants
• They absorb 10,000 times more infrared energy
  than CO2
• Levels are slowly declining but will remain for
  decades

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Future changes in climate

• Happening now higher temperatures, rising seas,
  heat waves, droughts, intense storms, season
  shifts, melting ice
• GHG levels are rising
• Along with fossil fuel demand and population
• Emissions will rise 35 (2030) and 100 (2050)
• Modeling global climate computing power has
  increased
• Can explore the potential future impacts of
  rising GHGs
• Atmospheric-ocean general circulation models
  (AOGCMs)
• Simulate long-term climatic conditions

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Significant findings of climate models

• Equilibrium climate sensitivity if atmospheric
  CO2 stays at 550 ppm (double preindustrial
  values), temperature will rise 3C (24.5C) by
  2050
• Higher latitudes and continental interiors will
  warm most
• But it will be warmer everywhere
• Snow cover and sea ice will decrease, opening up
  the Arctic Ocean by 2100
• Shrinking glaciers and ice caps will increase sea
  levels
• 90 of upper permafrost will thaw

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More findings

• Warmer, dilute upper layers of the North Atlantic
  Ocean will lead to decreased (but not collapsed)
  thermohaline circulation
• Increased storm intensities, higher wind speeds
  and waves, more intense precipitation
• More frequent, longer-lasting heat waves
• Longer growing seasons, shorter frost days
• Dry areas will get dryer, wet areas will get
  wetter
• Extreme droughts will affect up to 30 of the
  world
• Ecosystems (polar ecosystems, coral reefs,
  rainforests) will be profoundly affected,
  increasing species extinctions

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What about the Antarctic?

• The Antarctic could be a huge factor in rising
  sea levels
• Greenland and Antarctic ice sheets hold enough
  water to raise sea levels 230 feet
• Snowfall has not changed in the past 50 years
• 87 of the 244 glaciers are melting
• The melting ice sheet is raising sea levels 0.4
  mm/year
• Higher continental temperatures (3C)
• Models project a 5 snowfall increase for each
  1C temperature rise

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Climate change in the U.S.

• All impacts are expected to continue and/or
  increase
• Impacts are greater in Alaska than any other U.S.
  region
• Changes in the U.S. over the past 50100 years
  include
• Average temperature has risen 2F
• Wetter areas are wetter, dryer areas are dryer
• Heavy downpours and storms have increased
• More extreme and frequent weather events
• Stronger Atlantic hurricanes
• Arctic sea ice is declining rapidly

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Response to climate change

• Industries and transportation network are locked
  into using fossil fuels
• Massive emissions of GHGs will continue
• Adaptation anticipate harm and plan adaptive
  responses to decrease vulnerability of people,
  property, and the biosphere
• Mitigation take action to prevent emissions
• Skeptics about global warming exist
• Fossil fuel industry, Rush Limbaugh, conservative
  think tanks, some scientists