Climate change (global warming)

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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 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

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Chemistry we need to learn

• The Earths 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

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The Venetian atmosphere

• 450O C, 90 (Earth) atm.
• 96 CO2 with H2SO4 clouds
• Without CO2, T would be about 100O C

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Earths 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.

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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 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

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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 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!).

d
d-
Partial charges
Formal charges
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Radiation interacting with molecules
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Which vibrations of CO2 absorb IR radiation?
E
E
d-
d-
d-
d
d-
d
E
E
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The infrared absorption spectrum of
CO2wavenumber (cm-1) 10,000/wavelength (µm)
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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 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.

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Methane

• 40 from natural sources
• Decaying 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-1
• Termites (same chemistry)

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Nitrous oxide (NO2) laughing gas

• Bacterial conversion of nitrate (NO-3) from soils
• Catalytic converters
• Ammonia fertilizers
• Biomass burning
• Nylon and nitric acid manufacture

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CH4 natural gas production, landfills,
agriculture, global warming N2O NO3-
(bacteria), automobiles, industrial processes
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HCFC IR absorption
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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.

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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 Earths surface.
  Temperature of converted rain forests 3 higher
  (soil is darker than trees).

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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.

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3 standard deviations
2 standard deviations
1 standard deviation
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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.

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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

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Warming is unequivocal
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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

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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 3C.

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Probability of extreme weather events
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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.

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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.

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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 thought

• 85 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
oceans

• Stationary power plants
• Separating CO2 from methane (natural gas) in
  wells and pumping it back.

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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.

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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

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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 thats maybe
  80 of the problem

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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.

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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.