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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.