2 Past climate change and the natural greenhouse effect Climate changed throughout Earth’s historySometimes over millions of yearsOther times over a few decadesOver the past 900,000 years average temperature of atmosphere near the Earth’s surface has undergone prolonged periods ofGlobal cooling – thick glacial ice covered land for about 100,000 yearsGlobal warming – warmer interglacial period of melting lasting 10,000 to 12,500 years (last 10,000 years has been interglacial
3 Global effect and its significance For Earth to retain at a constant temperatureIncoming solar energy (visible light) must be balanced with outgoing energy (longer-length, lower energy infrared radiation) that cools the earthIn addition to incoming sunlight, a natural process called the greenhouse effect, warms the earth’s lower troposphereMolecules of greenhouse gases (mainly water vapor and carbon dioxide) warm the earth by absorbing some heat radiated by the earth’s surface.Causes their molecules to vibrate and transform the absorbed energy into longer-wavelength infrared radiation (heat) in the troposphere
4 Atmosphere does not behave like a real greenhouse since closed windows in a car or greenhouse keep air from being carried away by convection to outsideHeat released by molecules of greenhouse gases in the atmosphere is spread through the atmosphere by convectionThus it should be called tropospheric heating effectIf natural greenhouse effect acted by itself, the average temperature on earth’s surface would be 130o F
5 However, a natural cooling process occurs on the suface Large quantities of heat are absorbed by evaporation of liquid surface waterWater vapor molecules rise, condense to form droplets in clouds, and release their stored heat higher in the atmosphereThese combined effects means that the earth’s aveage surface temperature is about 59o FTwo greenhouse gases with largest concentrations in air areH2OCO2 (increases can occur from forest turnover in fall and winter)Others presentCH4 (natural)N2O (natural)CFC, SF6 SF5 CF3 (only from human sources)
6 Human Sources Rice paddies Burning fossil fuels Livestock wastes Coal production (leaks)Air conditionersPlastic foamsRefrigeratorsDeforestationUse of inorganic fertilizers
7 Since 1860, there has been a sharp rise in concentrations of CH4N2OThis is a strong indication of global warmingAnalysis of ancient ice showsConcentrations of CO2 in troposphere is higher that it has been in the past 420,000 years and is rising by 0.5% a year20th century was hottest in the past 1000 yearsSince 1860, average global temperature near the surface has risen by 0.6– 0.7o C ( o F)
8 Other Observed SignsIncreased temperatures and melting ice caps and floating iceRetreat of some glaciers in the Alps, Andes, Himalayas, and CascadesNorthward migration of some warm-climate fish and treesBleaching of coral reefs
9 Does this data indicate that our dramatic increase in fossil fuel use, agriculture, and deforestation have had an influence on earth’s temperature?Maybe to probably due to limited knowledge abut how complex our earth’s systems workSome of the increase may be due to fluctuations in average global temperature built into the earth’s systems or by human activitiesSuch warming could accelerate and last for decades to hundreds of years or could be temporary with a leveling offIt is clear that in the past 200 years, human activities have been changing the chemical composition of the atmosphere more rapidly than it has changed at anytime during the past 10,000 years
10 IPCC Intergovernmental Panel on Climate Change 2500 of world’s leading climate experts from 70 nationsEstablished by the UN and World Meteorological Organization1995 reportDiscernable human influence on climate in past 50 yearsEarth’s mean surface temperature is likely increase by o F between
11 Factors that Affect Climate Change Explain how each of the following affect the Earth’s climate.Changes in solar outputChanges in the Earth’s albedoModerating effect of oceansClouds and water vaporAir pollutionJet contrails
12 Possible effects of a warmer world We are looking at a projected global change in climate – not swings in local weatherDescribe what effects a warmer world would have inAgricultureWater resourcesBiodiversityWeather extremesHuman populationforestsSea level and coastal areasHuman health
13 Solutions with dealing with the threat of climate change Describe possible options in dealing with climate change.Describe how prevention can occur.Describe cleanup can occur.Explain how we can prepare for possible global warming.What were the results of the 1992 Earth Summit and the Kyoto Protocol?
14 Ozone Depletion in the Stratosphere Ozone (O3) keeps 95% UV radiation whichAllows human and other life forms to exist on EarthProtects humans fromSunburnCataracts – the clouding of th eyeImmune systems damagePrevents much O2 in the trophosphere to be converted to O3
15 Characteristics of CFCs which were called dream chemicals Measurements show seasonal depletion called thinning over Antarctica and ArcticThomas Migley Jr. Discovered the first chlorofluorocarbons (CFCs) in 1930 and created a family of highly useful onesTwo most widely used are CFC-11 and CFC-12 (CCl2F2) which are called freons used in refrigerationCharacteristics of CFCs which were called dream chemicalsStableOdorlessNonflammableNontoxicNoncorrosiveCheap to make
16 Uses Coolants Propellants in aerosol sprays Cleaners for electric partsSterilants in hospitalsFumigants for graineriesBubbles in plastic wraps
17 Too Good To Be TrueMolina and Rowland in 1974 indicated that CFCs were thinning the ozone in the stratosphereCalled a ban on all CFCsStated that large amounts were being released into the troposphere fromPropellants in spray cansLeaks in refrigerators and air conditionersProducction and burning of plastic foam productsCFCs reamin in the troposphere because they are insoluble in water and unreactiveOver years, they rise into the stratosphere through convection, random drift and turbulent mixingIn stratosphere, CFC molecules break down under the influence of UV radiation and release Cl-, reactive atom which speeds up the break down of ozoneEach CFC molecule can last in the stratosphere yearsEach Cl- can destroy 100,000 molecules of O3
18 CFC industry led by Dupont attacked Molina and Rowland but they stood their ground. Not until 1988 did nations agree to ban them and other ozone eaters and find substitutes in the Montreal Protocol in 1987 which went into effect in 1989Other ozone eatersHalons and HBFCs – used in fire extinguishersMethyl bromide (CH3Br) – used in fumigantsCarbon tetrachloride (CCl4) – used in CloroxMethylchloroform 1,1,1-trichloroethane (C2H3Cl3) - used as cleaning solvent for clothes and metals and as a propellant in dry-cleaning sprays, adhesives, and other aerosolsHydrogen chloride (HCl) – emitted by space shuttles
19 Seasonal Thinning of Ozone over the Poles 1984 – 40-50% of ozone over Antarctica was being destroyed during the Antarctica spring and summer when sunlight returnedLoss was significant after 1976 when large amounts were produced in the 1960s and even more in the 1970sThe ones produced in the 1980s have still to reach the stratosphereOzone thinning varies with altitude and locationIn 2000, thinning in Antarctica was largest ever covering an area 3 times the size of the U.S.
20 Each sunless winter, steady winds blow in a circular pattern ove the poles creating a polar vortex isolated until the sun returnsWater enters this circling stream of frigid air and forms ice crystalsIce crystals collect CFCs and others and speeds up their breakdown to release Cl atoms and ClOClO atoms combine with one another to form Cl2O2 molecules which cannot react with ozone and accumulate in the polar vortexWhen the sunlight returns in the spring, the light breaks up the stored ClO molecules releasing large amounts of Cl-Within weeks, 40-50% of the ozone is destroyed
21 The returning sunlight Gradually melts the ice crystalsBreaks up the vortex of trapped polar airAllows it to begin mixing againThen new ozone forms until next winterWhen the vortex breaks upHuge masses of depleted air above Antarctica flow northward and linger for a few weeks over Australia, New Zealand, South America, and South AfricaRaises damaging UV-B levels by 3-10% and up to 20%
22 More damaging UV-A and UV-B will reach the Earth and lead to There is some thinning in Arctic and will be at its worst betweenMore damaging UV-A and UV-B will reach the Earth and lead toWorse sunburnMore catarctsMore skin cancers likeBasal cell carcinomaMelanoma – the deadliest and which develops from a moleSquamous cellImmune system suppressionMore acidic deposition and eye-burning smogLower crop yields in key cropsDecline in forest productivityDegradation of materials like paint, plasticReduction in productivity of phytoplankton
23 Solutions for decreasing ozone depletion Substitutes like HC (hydrocarbons like propane, butane) are a way to prevent ozone depletionHCFs break down faster and HFCs do not contain chlorine
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