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Climate change (global warming) The issues: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? 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?
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Evidence and proposals for changeWhat is the evidence? Is it
compelling?What is the scientific consensus? Climate models and
their predictionsConsequences of the predictionsStrategies for
change
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Chemistry we need to learnThe Earths energy balance - the
greenhouse effectThe shapes of molecules - valence shell electron
pair repulsion (VSEPR) theoryMolecular vibrations how they absorb
IR radiationMasses and moles - weighing to count molecules
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The Venetian atmosphere450O C, 90 (Earth) atm.96% CO2 with H2SO4
cloudsWithout CO2, T would be about 100O C
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Earths atmosphereThe 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.
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The Earths energy balance
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Ice core samples from Antarctica
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Correlation between CO2 and temperature
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Post industrial revolution CO2 levels
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Post industrial revolution temperature changes
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Correlation or causalityThis is a much tougher problem than
ozone.Many more variablesBoth positive and negative feedbacksVastly
greater scale scientifically, economically and politicallyNeed to
establish a mechanismNeed to develop and refine climate models
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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.
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Charge separation in covalent bondsElectrons 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!).
+-Partial chargesFormal charges
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Radiation interacting with molecules
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Which vibrations of CO2 absorb IR radiation? -+--+-EEEE
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The infrared absorption spectrum of CO2[wavenumber (cm-1) =
10,000/wavelength (m)]
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Why do some vibrations absorb IR radiation while others dont
?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.
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Earths carbon cycle
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Methane and other greenhouse gasesGenerally 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.
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Methane40% from natural sourcesDecaying vegetation, marsh
gas.Agriculture, especially rice paddies with anaerobic
bacteria.Ruminants (cattle and sheep) you dont want to know where
it comes from! 500L cow-1 day-1Termites (same chemistry)
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Nitrous oxide (NO2) laughing gasBacterial conversion of nitrate
(NO-3) from soilsCatalytic convertersAmmonia fertilizersBiomass
burningNylon and nitric acid manufacture
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CH4: natural gas production, landfills, agriculture, global
warmingN2O: NO3- (bacteria), automobiles, industrial processes
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HCFC IR absorption
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Radiative forcingGlobal 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.
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Difficulties in modeling climate change: scientificEstablishing
anthropogenic origins.Feedbacks, positive (de-stabilizing) and
negative (stabilizing).Oceans competing effectsWarming releases CO2
(Coke)Warming may or may not increase plankton growth. Particulates
smoke, haze, aerosols. Are they net reflectors or absorbers?Albedo
reflectivity of Earths surface. Temperature of converted rain
forests 3 higher (soil is darker than trees).
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IPCC 2007 terminologyConfidence terminology degree of confidence
in scientific understanding. 10% levels of separationLikelihood
terminology likelihood of a particular occurrence/outcome. Gaussian
probabilities expressed as numbers of standard deviationsThere is
much overlap between these in the report.
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2 standard deviations1 standard deviation3 standard
deviations
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Anthropogenic climate change driversCO2, 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.
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Anthropogenic climate change driversRadiative forcing from CO2,
methane and nitrous oxide is +2.30 W m-2 ( 10%)Other gases
contribute about + 0.7 W m-2Aerosols 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
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Warming is unequivocal
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Warming is unequivocalRates 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
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Warming is unequivocalNew 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 3C.
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Probability of extreme weather events
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Paleoclimate perspectiveWarmth 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.
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Understanding and attributing climate changeIt 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.
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Natural forcings only would have cooled
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Anthropogenic with natural forcings fit
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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.
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Food for thought85% of our the worlds 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.
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Increasing global CO2 emissions and changing sources
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A promising approach - CO2 sequestration in the oceansStationary
power plantsSeparating CO2 from methane (natural gas) in wells and
pumping it back.
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The Kyoto Protocol1990 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.
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The Kyoto Protocol - where are we?New agreements reached in 2001
in BonnThe 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
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Copenhagen accordChina wants it both ways$ 100B yr-1 promised to
developing nationsTargets for reductions submitted by 38 countries
January 31, 2010Reducing intensity (emissions per unit of GDP)
seems like an end around to meIf US and BRIC could reach consensus
thats maybe 80% of the problem
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Climate change summaryMuch 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.
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Climate change summaryThe 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.
*Length of column is mean; error bars are shown.*