Download File - Physical Science

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 Earth’s 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 IPCC’s 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 IPCC’s 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 manmade 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: 1400–1850
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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 Earth’s
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
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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 water’s 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 doesn’t 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, Earth’s 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 Earth’s 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 -19°C instead of
+14°C
• Life would be impossible
• Earth’s 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
• China’s and India’s pollution has increased aerosols
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Global warming and cooling
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Solar variability
• Variation in the Sun’s 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 1997–2008
• 2005 set a record high—the warmest since the late
1800s
• The average global temperature has risen 0.6°C since
the mid-1970s (0.2°C/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 Earth’s 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 5°F in
summer, 10°F 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 0.5°–0.85°C
• The West Antarctic Ice Sheet (WAIS) is shrinking and
can raise sea levels by 16–20 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 ocean’s chemistry is actually changing
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Carbon dioxide levels
• CO2 levels oscillate 5–7 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 3°C (2°–4.5°C) 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 (3°C)
• Models project a 5% snowfall increase for each 1°C
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 50–100 years
include
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Average temperature has risen 2°F
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
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