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BELLRINGER
EXPLAIN IN COMPLETE SENTENCES
WHAT IS CONTENT AND MECHANISMS
OF THE GREENHOUSE EFFECT
Climate change (global warming)
The issues:
1. Are humans responsible for most of the global
temperature rise of the past century or so, or is the
increase just a typical fluctuation in global
temperature?
2. If most of the temperature rise can be attributed to
increases in anthropogenic CO2 emissions, what
are the likely consequences if no action is taken to
curb these emissions?
Evidence and proposals for change
 What is the evidence? Is it compelling?
 What is the scientific consensus?
 Climate models and their predictions
 Consequences of the predictions
 Strategies for change
Chemistry we need to learn
 The Earth’s energy balance - the greenhouse effect
 The shapes of molecules - valence shell electron pair
repulsion (VSEPR) theory
 Molecular vibrations – how they absorb IR radiation
 Masses and moles - weighing to count molecules
The Venetian atmosphere
Fig. 3.1
450O C, 90 (Earth) atm.
96% CO2 with H2SO4 clouds
Without CO2, T would be about 100O C
Earth’s atmosphere
 The Earth is about 33OC warmer than expected if we consider
only the amount of solar energy received and reflected.
 Trace atmospheric gases, H2O and CO2, trap infrared radiation
that would otherwise be re-emitted into space.
 This effect is known as the Greenhouse Effect - the mechanism
that keeps greenhouses hotter than we might expect.
The Earth’s energy balance
Ice core samples from Antarctica
Correlation between CO2 and temperature
Post industrial revolution CO2 levels
Post industrial revolution temperature changes
Correlation or causality
 This is a much tougher problem than ozone.
 Many more variables
 Both positive and negative feedbacks
 Vastly greater scale scientifically, economically
and politically
 Need to establish a mechanism
 Need to develop and refine climate models
How does electromagnetic radiation interact
with molecules ?
 Electromagnetic radiation consists of oscillating electric
and magnetic fields.
 The electric field interacts most strongly.
 An electric field is an imaginary construct - if a charged
particle experiences a force that causes it to move, we
say that it is interacting with an electric field.
 Charges of opposite signs move in opposite directions
under the influence of an electric field.
Charge separation in covalent bonds
 Electrons are not shared equally between two
atoms of different elements.
 The electrons in the bond will tend to favor the
element with the greatest nuclear charge
(Coulomb again!).
δ+
Formal charges
δ-
Partial charges
ACTIVITY
DRAW THE FIGURE EXPLAINING THE
GREENHOUSE EFFECT
GIVE DETAILS AND EXPLAIN
Radiation interacting with molecules
Which vibrations of CO2 absorb IR radiation?
E
δ-
E
E
δ+
δ-
δ-
E
δ+
δ-
The infrared absorption spectrum of CO2
[wavenumber (cm-1) = 10,000/wavelength (µm)]
Why do some vibrations absorb IR radiation
while others don’t ?
 The partial charges on the atoms must move under the
influence of the electric field in a way that excites the
vibration.
 Exciting the symmetric CO2 stretch would require the two
partially negative O atoms to move in different directions
under the influence of the same electric field - impossible.
 Exciting the antisymmetric stretch of H2O would require
the O atoms to move in different directions under the
influence of the same electric field - impossible.
Earth’s carbon cycle
Methane and other greenhouse gases
 Generally present at lower concentrations than CO2.
 More complicated molecules with more polar bonds have
more and stronger IR absorption bands – global warming
potential (GWP).
 Relative importance is given by the product of
concentration and GWP.
 Atmospheric lifetime is important – of the long-lived
greenhouse gases (LLGHGs), methane has the shortest
lifetime, being susceptible to reaction with OH.
Methane
 40% from natural sources
 Decaying vegetation, marsh gas.
 Agriculture, especially rice paddies with anaerobic
bacteria.
 Ruminants (cattle and sheep) – you don’t want to
know where it comes from! 500L cow-1 day-1
 Termites (same chemistry)
Nitrous oxide (NO2) “laughing gas”
 Bacterial conversion of nitrate (NO-3) from soils
 Catalytic converters
 Ammonia fertilizers
 Biomass burning
 Nylon and nitric acid manufacture
CH4: natural gas production, landfills, agriculture, global warming
N2O: NO3- (bacteria), automobiles, industrial processes
HCFC IR absorption
Radiative forcing
 Global warming potentials have been converted to
radiative forcings for climate models.
 Radiative forcing (RF) is defined as the net (down
minus up) energy flux in watts per square meter.
Difficulties in modeling climate change: scientific
 Establishing anthropogenic origins.
 Feedbacks, positive (de-stabilizing) and negative (stabilizing).
 Oceans – competing effects
 Warming releases CO2 (Coke)
 Warming may or may not increase plankton growth.
 Particulates – smoke, haze, aerosols. Are they net reflectors or
absorbers?
 Albedo – reflectivity of Earth’s surface. Temperature of
converted rain forests 3° higher (soil is darker than trees).
IPCC 2007 terminology
 Confidence terminology – degree of confidence in
scientific understanding. 10% levels of separation
 Likelihood terminology – likelihood of a particular
occurrence/outcome. Gaussian probabilities
expressed as numbers of standard deviations
 There is much overlap between these in the report.
3 standard deviations
2 standard deviations
1 standard deviation
Anthropogenic climate change drivers
 CO2, methane and nitrous oxide concentrations far
exceed natural range over past 650,000 years - most
of the increase has been post-industrial revolution.
 CO2 from 280 ppm to 380 ppm.
 Methane from 715 ppb to 1775 ppb.
 Nitrous oxide from 270 ppb to 320 ppb.
Anthropogenic climate change drivers
 Radiative forcing from CO2, methane and nitrous
oxide is +2.30 W m-2 (± 10%)
 Other gases contribute about + 0.7 W m-2
 Aerosols provide net cooling of about -1.2 W m-2.
Uncertainty in this estimate is the dominant
uncertanty in radiative forcing.
 Net forcing is + 1.6 W m-2
Warming is unequivocal
Warming is unequivocal
 Rates of surface warming have increased, with 11 of the
past 12 years being the warmest since 1850.
 Balloon and satellite data confirm same trend in the
atmosphere, clearing up a discrepancy from TAR.
 Water vapor content has increased.
 Ocean temperatures have increased to depths of at least
3 km; oceans absorb 80% of added heat.
 Mountain glaciers and snow cover have declined in
both hemispheres
Warming is unequivocal
 New data since TAR show that it is very likely that
Greenland and Antarctic ice sheet losses have led to sea
level rises.
 Rates of sea level rise have increased from about 2 mm
year-1 (1961 – 2003) to about 3 mm year-1 (1993 –
2003). High confidence of 19th - 20th century increase.
 Arctic temperatures have increased at twice the global
average rates and permafrost temperatures have
increased by about 3°C.
Probability of extreme weather events
Paleoclimate perspective
 Warmth of last 50 years is very likely higher than any
50 year period in last 500 years and likely the highest
in last 1,300 years.
 Global average sea levels in the last interglacial
period (125,00 years ago) was likely 4 – 6 m higher
than in 20th century due to retreat of polar ice.
Understanding and attributing climate change
 It is extremely unlikely that global warming patterns
can be explained without external forcing.
 It is very likely that anthropogenic greenhouse gases
have contributed to most of the warming.
 Without atmospheric aerosols it is likely that
temperature rises would have been greater.
Natural forcings only would have cooled
Anthropogenic with natural forcings fit
What can we do?
What should we do?
 Act now - the evidence is clear and compelling.
 Study more - although suggestive, the evidence is
not conclusive.
 Do nothing - climate change is inevitable.
Food for thought
 85% of our the world’s total energy needs are
provided by fossil fuels.
 The timescale for change is long.
 Per capita emissions are misleading. As the
populous underdeveloped countries (China, India)
industrialize, even small percentage growth rates
have large total effects.
Increasing global CO2 emissions and changing sources
A promising approach CO2 sequestration in the oceans
 Stationary power plants
 Separating CO2 from methane (natural gas) in
wells and pumping it back.
The Kyoto Protocol
 1990 IPCC certified the scientific basis for global climate
change.
 Kyoto Conference in 1997 - 161 countries were represented.
 Binding emissions targets were set for six greenhouse gases for
38 countries; the goal was to reduce emissions by 5% around
2010.
 Emissions credit trading was established.
 Emissions credit could also be given by helping developing
nations reduce emissions through improved technology.
The Kyoto Protocol - where are we?
 New agreements reached in 2001 in Bonn
 The U.S. did not participate.
 84 countries signed and 37 countries have ratified the
treaty, including the European Union as a bloc, and
Japan.
 The sticking point for the U.S. has been (starting with
the Clinton administration) the failure to agree on limits
for key developing countries.
 Russia signed in 2004 in exchange for WTO status
Copenhagen accord
 China wants it both ways
 $ 100B yr-1 promised to developing nations
 Targets for reductions submitted by 38 countries
January 31, 2010
 Reducing intensity (emissions per unit of GDP)
seems like an end around to me
 If US and BRIC could reach consensus that’s
maybe 80% of the problem
Climate change summary
 Much if not all recent increases in global temperatures
are due to anthropogenic sources.
 Global temperatures and CO2 concentrations in ice cores
are strongly correlated.
 The shapes of molecules can be understood using
VSEPR theory.
 Only certain vibrations of molecules will absorb infrared
radiation and be effective greenhouse gases.
Climate change summary
 The relative importance of various greenhouse gases is
given by their relative abundance and global warming
potential.
 Controlling population growth and economic development,
energy conservation, alternate energy sources, and CO2
sequestration are key elements in mitigating climate
change.