Chapter 18 Topics:
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The Earth’s climate
system
Human influences on the
atmosphere and climate
Methods of climate
research
Impacts of global
climate change
Ways we can respond
to climate change
What is climate change?
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Climate science is the fastest-developing area of
environmental science
Global climate change = describes trends and
variations in Earth’s overall climate
Global warming = an increase in Earth’s average
temperature (one part of global climate change)
Earth’s climate has varied naturally through time, but the
current rapid changes in climate are due to human
actions that have increased greenhouse gases
Understanding climate change requires understanding
how our planet’s climate works
Climate factors
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The sun = without it, Earth would be dark and
frozen; provides energy for three of Earth’s systems
How Earth tilts (amount and direction) and the
shape of Earth’s orbit influence long-term climate
variations (orbital variations – Milankovitch cycles)
The atmosphere = without it, Earth’s temperature
would be much colder
The oceans = shape climate by storing and
transporting heat and by providing moisture
Climate factors – cont’d
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Latitude = determines whether a place received
direct sunlight, indirect sunlight, or a seasonal
alternation of direct and indirect
Geography = altitude influences temperature;
mountain ranges can be barriers to the movement
of moisture-laden air masses (orographic effect)
Continental configuration = influences the distance
to the ocean (availability of moisture) and the
pattern of the ocean’s surface currents
Earth’s energy budget
Heating the troposphere
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As Earth’s surface absorbs solar radiation, the surface
increases in temperature and emits infrared radiation
Greenhouse gases = atmospheric gases that absorb
infrared radiation (water vapor, carbon dioxide, nitrous
oxide, methane, chlorofluorocarbons [CFCs])
After absorbing radiation, greenhouse gases re-emit
infrared energy, losing some energy to space
Greenhouse effect = energy that travels downward,
warming the atmosphere and the planet’s surface
The greenhouse effect is natural
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Greenhouse gases have always been in the atmosphere
We are not worried about the natural greenhouse
effect
We are concerned with Anthropogenic intensification of
the greenhouse effect
Global warming potential = the relative ability of one
molecule of a greenhouse gas to contribute to warming
Expressed in relation to carbon dioxide (potential = 1)
 Methane is 25 times as potent as carbon dioxide
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Carbon dioxide leads the way
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Carbon dioxide is not the most potent greenhouse
gas, but it is extremely abundant
CO2 exerts six times more impact than methane,
nitrous oxide, and halocarbons combined
Human activities have increased atmospheric CO2
from 280 parts per million (ppm) to 389 ppm, the
highest levels in more than 800,000 years
Then and now
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Carbon dioxide is removed from the atmosphere by
the deposition, partial decay, and compression of
organic matter (plants) in wetlands or marine areas
These processes formed coal, oil, and natural gas
which have remained buried for millions of years
Burning fossil fuels transfer CO2 from lithospheric
reservoirs into the atmosphere, and it is the main
reason atmospheric carbon dioxide concentrations
have increased so dramatically
Carbon dioxide flux
Other greenhouse gases
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Water vapor = the most abundant greenhouse gas
 Contributes
most to the natural greenhouse effect
 Concentrations have not changed
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Methane = fossil fuel extraction, natural gas
distribution leaks, livestock, landfills, crops (rice)
Nitrous oxide = feedlots, chemical manufacturing
plants, auto emissions, synthetic nitrogen fertilizers
Halocarbon gases (CFCs) are declining due to the
Montreal Protocol
Uncertain feedbacks
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Tropospheric warming will transfer more water to
the atmosphere, and then…?
A positive feedback loop = more water vapor …
more warming … more evaporation … more water
vapor …
A negative feedback loop = more water vapor …
more clouds … shade and cool Earth … decrease
evaporation
Minor modifications of the atmosphere can lead to
major effects on climate
Aerosols have varying effects
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Aerosols = microscopic droplets and particles
Soot (black carbon aerosols) causes warming by
absorbing solar energy
Most tropospheric aerosols cool the atmosphere by
reflecting the sun’s rays
 Sulfate
aerosols produced by fossil fuel combustion may
slow global warming, at least in the short term
 Volcanic eruptions reduce sunlight reaching Earth’s
surface and cool the Earth; effects generally last for
three to five years [1816 – “the year without summer”]
Radiative forcing
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The relative contribution
of warming and cooling
factors is described
using the concept of
radiative forcing
Earth is experiencing
radiative forcing of 1.6
watts/m2 more than it is
emitting to space
Milankovitch cycles
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Milankovitch cycles =
periodic changes in the tilt
of Earth’s axis and shape
of its orbit around the sun
Alter the way solar
radiation is distributed
over Earth by modifying
patterns of atmospheric
heating
Reasonable evidence
linking these cycles to
periods of cold glaciation
and warm interglacial
times
Ocean’s dual roles
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Carbon dioxide
 Ocean
absorption = the ocean holds 50 times more
carbon than the atmosphere, slowing global warming
but not preventing it
 Warmer oceans absorb less CO2, a positive feedback
effect that accelerates warming
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Thermal energy
 Tropical
oceans absorb large amounts of thermal
energy
 Ocean currents move warm water toward the poles
where the energy is release to the atmosphere
Knowing about climate
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Direct measurements give information about the
present and the (geologically) recent past
Historical records of severe events
 Temperature measurements go back 100 years
 Ocean/atmospheric chemistry testing began in 1958
 Satellite measurements began in the 1980s
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Proxy indicators (indirect evidence that substitutes
for direct measurements) give information about
paleoclimates
Proxy indicators
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Trapped bubbles/particulates in ice cores provide a
timescale of atmospheric composition, temperature
trends, snowfall, solar activity, volcanic eruptions, and
frequency of fires
Antarctic ice cores extend back 800,000 years, across
eight cycles of glaciation and deglaciation
Sediment cores preserve pollen grains, plant remnants
Tree rings show age, precipitation, and fire history
In arid regions, packrats carry seeds and plants to their
middens (dens)
Computer modeling
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Computer models of climate systems helps us test
our understanding of these systems and help us
make predictions about future climate conditions
Successful recreation of
the past gives confidence
in prediction of the future
Different factors can be
in/excluded to assess
relative effects
Studying current climate change
Intergovernmental Panel on Climate Change (IPCC),
hundreds of international scientists and government
officials, was established in 1988
 The IPCC Reports summarize thousands of studies,
synthesize scientific information concerning climate
change, and present a global consensus of scientific
climate research
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Document observed trends in surface temperature,
precipitation patterns, snow and ice cover, sea levels, storm
intensity, etc.
 Predict impacts of current and future climate change on
wildlife, ecosystems, and human societies
 Discuss strategies to pursue in response to climate change
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Current consensus
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Scientific evidence that climate has changed is
overwhelming – we now have over 30 years of globally
distributed, direct (satellite) measurement of a wide
range of climate-relevant information
Scientific evidence linking a warming Earth to increased
levels of CO2, and linking the increased CO2 to the
burning of fossil fuels is very strong
Average temperature has increased 0.74°C since 1906
Most of the increase occurred in the last few decades
 The 16 warmest years on record have been since 1990
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Future temperatures
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Temperatures are predicted to rise 0.4°C in the
next 20 years
At the end of the 21st century, temperatures could
be 1.8–4.0 °C higher than today’s
A
greater number of unusually hot days, heat waves
 Polar areas will have the most intense warming
 Sea surface temperatures are expected to rise,
allowing hurricanes and tropical storms to increase in
power and duration
Projected temperature changes
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Projected increases in surface temperature for
2090–2099 relative to 1980–1999
Future precipitation
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Some regions are likely to receive more precipitation
than usual, and others might receive less
The intensity of precipitation and the distribution of
rainfall among events of specific intensities will change
Droughts are expected to become more frequent and
severe, harming agriculture, promoting soil erosion,
reducing water supplies, and triggering fires
Heavy rains are expected to contribute to flooding,
killing people, destroying homes, and inflicting billions
of dollars in damage
Projected precipitation changes
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Precipitation will increase at high latitudes and
decrease at low and middle latitudes
Ice caps, glaciers, permafrost
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Mountaintop glaciers are disappearing
 Glaciers
on tropical mountaintops have disappeared
 The remaining 26 of 150 glaciers in Glacier National
Park will be gone by 2020 or 2030
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Melting of Greenland’s ice sheet is accelerating
Warmer water is melting Antarctica’s coastal ice
shelves, accelerating ice drainage from the interior
Permafrost (permanently frozen ground) is thawing,
destabilizing soil, buildings, etc. and releasing
methane
Sea level
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Sea levels are rising
 Influx
from melting of land-based ice-caps and glaciers
 Thermal expansion as the ocean becomes warmer
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Rising sea levels will create
significant problems
 53%
of people in the U.S.
live in coastal areas
 Costs will be incurred either
for relocation or for
“armoring” of existing
infrastructure
Climate change affects organisms
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Organisms are adapted to their environments, and they
are affected when those environments change
Global warming modifies temperature-dependent
phenomena (e.g., timing of migration, breeding)
Animals and plants will move toward the poles or
upward in elevation
20–30% of species will be threatened with extinction
 Rare species will be pushed out of preserves
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Droughts, fire, and disease will decrease plant growth,
and fewer plants means more CO2 in the atmosphere
Close up on coral reefs
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Coral reefs are habitat for food fish, and snorkeling
and scuba diving sites for tourism
Warmer waters contribute to coral bleaching which
kills corals
Increased CO2 is acidifying the ocean, so organisms
can’t build their exoskeletons
Oceans have already decreased by 0.1 pH unit,
which is enough to kill most coral reefs
Climate change affects people
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Societies are feeling the impacts of climate change
Agriculture: shortened growing seasons, decreased
production, crops more susceptible to droughts,
increasing hunger
Forestry: increased fires, invasive species, insect and
disease outbreaks
Health: heat waves and stress can cause death
 Respiratory
ailments, expansion of tropical diseases
 Disease and sanitation problems from flooding
 Drowning from storms
Focus on heat waves
Climate change affects economics
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Costs will outweigh benefits of climate change
It will widen the gap between rich and poor, and those
with less wealth and technology will suffer most
External costs of damages will be $10–350/ton of
carbon
It will cost 1–5% GDP on average globally; poor
nations will lose more than rich ones
The Stern Review predicts it will cost 5–20% of GDP by
2200, but investing 1% of GDP now could avoid these
costs
Impacts will vary regionally
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Where we live will determine how we experience the
impacts of climate change
Temperature changes have been greatest in the Arctic
Melting ice sheets, thinning ice, increasing storms, etc.
 Harder for people and polar bears to hunt
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U.S. temperatures will continue rising
Plant communities will shift north and upward
 More frequent extreme weather events
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The southern U.S. will get drier, the northern wetter
Sea levels will rise and may be worse in the East
Focus on the US
Cause-and-effect diagram
Responding to climate change
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There are two broad approaches human society can
take to respond to global warming and the resulting
climate change.
Mitigation = pursue actions that reduce greenhouse
gas emissions to lessen severity of future climate change
Energy efficiency, renewable energy
 Preventing deforestation, protecting soils
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Adaptation = pursue actions that reduce the impacts of
the changes that have and can be predicted to happen
Seawalls, “armored” infrastructure
 Adjusting agricultural practices, preparing for heat waves
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A balanced response
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Adaptation: even if we
stopped all emissions,
warming would continue
Mitigation: if we do
nothing, we will be
overwhelmed by climate
changes
The faster we reduce
our emissions, the less
we will alter the climate
Reducing emissions - electricity
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The largest source of U.S. CO2 emissions
 70%
of electricity comes from fossil fuels
 Coal causes 50% of emissions
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To reduce fossil fuel use:
 Encourage
conservation and efficiency
 Switch to cleaner and/or renewable energy sources
 The EPA’s Energy Star Program
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Carbon capture = removes CO2 from emissions
Carbon sequestration (storage) = stores carbon
underground where it will not seep out
Reducing emissions - transportation
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2nd largest source of U.S. greenhouse gases
 Cars
are inefficient
 Only14 and 25% of gasoline energy becomes motion
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Ways to help:
 More
efficient cars
 Hybrid or electric cars
 Drive less and use public transportation
 Live near your job, so you can bike or walk
Reducing emissions - other
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Agriculture:
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Forestry:
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Reforest cleared land and preserve existing forests
Sustainable forestry practices
Waste management:
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Sustainable land management lets soil store more carbon
Reduce methane emissions from rice and cattle
Grow renewable biofuels
Treating wastewater
Generating electricity by incinerating waste
Recovering methane from landfills
Individuals can recycle, compost, reduce, or reuse goods
Multiple strategies needed
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There is no magic bullet for mitigating climate
change
Most reductions can be achieved using current
technology that we can use right away
Stabilization triangle = a portfolio of strategies,
each one feasible in itself, that could stabilize CO2
emissions
Reducing 1 billion tons of carbon per year for 50
would eliminate one of the seven “wedges”
The “Wedge” concept
International efforts
U.N. Framework Convention on Climate Change = a
plan to reduce greenhouse gas emissions to 1990 levels
by 2000 through a voluntary, nation-by-nation
approach
 By the late 1990s, it was clear that the voluntary
approach would not succeed
 Developing nations created a binding international
treaty requiring emission reductions
 The Kyoto Protocol = between 2008 and 2012,
signatory nations must reduce emissions of six
greenhouse gases to levels below those of 1990
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Kyoto Protocol
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This treaty took effect in 2005 after Russia became the
127th nation to ratify it
The United States will not ratify the Kyoto Protocol
It requires industrialized nations to reduce emissions
But it does not require industrializing nations (China and
India) to reduce theirs
Other countries resent the U.S. because it emits 20% of
the world’s greenhouse gases but won’t take action
In 2007, one delegate said, “If for some reason you
are not willing to lead...please get out of the way.”
The Copenhagen Conference
The conference in 2009 tried to design a successor
treaty to the Kyoto Protocol
 Nations hoped the U.S., under President Obama, would
participate in a full international agreement
 Obama would not promise more than Congress had
agreed to
 In a last-minute deal, developed nations will help
developing nations pay for mitigation and adaptation
 Nations that reduce deforestation will be rewarded
 Nothing is legally binding and no targets are set
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States and cities step up
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The U.S. federal government is not taking
action, but state and local governments are
By 2010, 1,000 mayors signed the U.S.
Mayors Climate Protection Agreement to meet or
beat Kyoto Protocol guidelines
California passed the Global Warming Solutions
Act to cut emissions 25% by 2020
Regional Greenhouse Gas Initiative
(RGGI) in 2007, 10 northeastern states set up a
cap-and-trade program
Impacts to the economy?
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Many people in the U.S. feel that emissions reductions
will hurt the economy
China and India also resist emissions cuts
Economic vitality does not need higher emissions –
Germany cut emissions by 21%, the U.K. by 17%
Industrialized nations will gain from energy transitions
They invent, develop, and market new technologies
The future will belong to nations willing to develop new
technologies and energy sources
Economic policy tools
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Permit trading programs harness the economic
efficiency of the free market to achieve policy goals
 Businesses
have flexibility in how they meet the goals
 Polluters choose how to cut their emissions
 They are given financial incentives to reduce them
The Regional Greenhouse Gas Initiative
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Each state decides which polluting sources participate
Each state sets a cap on total CO2 emissions it allows
Each emissions source gets one permit for each ton they
emit, up to the amount of the cap
Each state lowers its cap over time
States with too few permits must reduce emissions, buy
permits from others, or pay for carbon offsets
Sources with too many permits may sell them
Any source emitting more than permitted will be
penalized
Other existing exchanges
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Chicago Climate Exchange = the world’s first
emissions trading program for greenhouse gas
reduction
 350
corporations, institutions, etc.
 Voluntary but legally binding trading system aims for a
6% reduction in emissions by 2010
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The European Union Emission Trading Scheme
 The
world’s largest cap-and-trade program
 Governments had allocated too many permits
Other options
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Carbon tax = governments charge polluters a fee
for each unit of greenhouse gases they emit
 Polluters
have a financial incentive to reduce emissions
 European nations, British Columbia, and Boulder,
Colorado have carbon taxes
 Polluters pass costs on to consumers
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Fee-and-dividend = funds from the carbon tax
(fee) are passed to taxpayers as refunds
(dividends)
Other options – cont’d
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Carbon offset = a voluntary payment intended to
enable another entity to reduce the greenhouse
emissions that one is unable to reduce oneself
 The
payments offset one’s own emissions
 Popular among utilities, businesses, universities,
governments
 Trying to achieve carbon-neutrality, no net carbon
emitted
 Needs rigorous oversight to make sure that the offset
money accomplishes what it is intended for