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Climate change (global warming)

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Title: Climate change (global warming)


1
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?

2
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

3
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

4
The Venetian atmosphere
  • 450O C, 90 (Earth) atm.
  • 96 CO2 with H2SO4 clouds
  • Without CO2, T would be about 100O C

5
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.

6
The Earths energy balance
7
Ice core samples from Antarctica
8
Correlation between CO2 and temperature
9
Post industrial revolution CO2 levels
10
Post industrial revolution temperature changes
11
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

12
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.

13
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
14
Radiation interacting with molecules
15
Which vibrations of CO2 absorb IR radiation?
E
E
d-
d-
d-
d
d-
d
E
E
16
The infrared absorption spectrum of
CO2wavenumber (cm-1) 10,000/wavelength (µm)
17
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.

18
Earths carbon cycle
19
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.

20
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)

21
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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23
CH4 natural gas production, landfills,
agriculture, global warming N2O NO3-
(bacteria), automobiles, industrial processes
24
HCFC IR absorption
25
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.

26
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).

27
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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29
3 standard deviations
2 standard deviations
1 standard deviation
30
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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35
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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38
Warming is unequivocal
39
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

40
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.

41
Probability of extreme weather events
42
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.

43
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.

44
Natural forcings only would have cooled
45
Anthropogenic with natural forcings fit
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50
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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52
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.

53
Increasing global CO2 emissions and changing
sources
54
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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56
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.

57
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

58
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.

61
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.
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