Climate Change Alan Campion

61
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 CO 2 emissions, what are the likely consequences if no action is taken to curb these emissions?

description

Global warming and its effect

Transcript of Climate Change Alan Campion

  • 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?

  • 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

  • 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

  • The Venetian atmosphere450O C, 90 (Earth) atm.96% CO2 with H2SO4 cloudsWithout CO2, T would be about 100O C

  • 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.

  • The Earths energy balance

  • Ice core samples from Antarctica

  • Correlation between CO2 and temperature

  • Post industrial revolution CO2 levels

  • Post industrial revolution temperature changes

  • 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

  • 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 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

  • Radiation interacting with molecules

  • Which vibrations of CO2 absorb IR radiation? -+--+-EEEE

  • The infrared absorption spectrum of CO2[wavenumber (cm-1) = 10,000/wavelength (m)]

  • 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.

  • Earths carbon cycle

  • 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.

  • 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)

  • Nitrous oxide (NO2) laughing gasBacterial conversion of nitrate (NO-3) from soilsCatalytic convertersAmmonia fertilizersBiomass burningNylon and nitric acid manufacture

  • CH4: natural gas production, landfills, agriculture, global warmingN2O: NO3- (bacteria), automobiles, industrial processes

  • HCFC IR absorption

  • 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.

  • 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).

  • 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.

  • 2 standard deviations1 standard deviation3 standard deviations

  • 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.

  • 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

  • Warming is unequivocal

  • 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

  • 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.

  • Probability of extreme weather events

  • 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.

  • 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.

  • 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 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.

  • Increasing global CO2 emissions and changing sources

  • A promising approach - CO2 sequestration in the oceansStationary power plantsSeparating CO2 from methane (natural gas) in wells and pumping it back.

  • 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.

  • 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

  • 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

  • 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.

  • 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.*