1Chapter 14: The Changing Climate Detecting Climate ChangeNatural Causes of Climate ChangeAnthropogenic Causes of Climate ChangePossible Consequences of Global WarmingNYCClimate•More than just ‘average weather’•Extreme events & probability•Sum of all statistical weather information describing a place or regionElements of WAC1. Temperature of Air2. Humidity of Air3. Cloud Cover (type and amount)4. Precipitation (type and amount)5. Air Pressure6. Wind Speed and Direction2The Climate SystemEarth’s four spheres1. Lithosphere2. Atmosphere3. Hydrosphere4. BiosphereClimate Change?-Paleo studies show climate varies on every temporal scale -Human activities are changing climate-Recent data indicates climate is becoming more variable-modern record is ~200 years-satellites 1980s3Measuring Climate Change-Seafloor sediments-Oxygen isotope ratios-Old Soils-Tree Rings: Dendrochronology-Historical documentsSea-Floor SedimentsOrganisms at the surfaceBalance between ocean surface waters and the atmosphereAs climate changes so does the composition of the surface organismsRecorded in sediments as the organisms die4Rates of Sedimentation• Ocean Basins: slow, pelagic sediments– 0.5 – 1.0 cm/ 1000 years– Average Accumulation 500 – 600 m– Thickness depends on age– Oldest sea floor is 200 million years5BiogenousSiliceous (SiO2)diatoms, radiolaria (photosynthetic)ocean is under-saturated dissolves quicker in warm waterDiatoms = cool regionsRadiolaria = warmer regionsBiogenousCalcareous (CaCO3)cocolithophorids, pteropods, foraminiferadominant pelagic sedimentLysocline = calcium carbonate dissolvesCCD = dissolution equals accumulation 4500m6Oxygen Isotope Analysis from Ice CoresIsotope = One of two or more atoms having the same atomic number (number of protons) but different mass numbers (protons + neutrons)18O 16O ratiosWater forms with either16O evaporates easierOxygen Isotope Analysis from Ice CoresPrecipitation & glacial ice are enriched in 16OOceans are enriched in 18OOcean18O ice ages16O increases warmer periodscocolithophorids, pteropods, foraminifera = record ratios in their shells (CaCO3)7Oxygen Isotope AnalysisTemperature Variations18O more easily evaporated during warm periodsIce cores record the warm periodsPockets of air within the crystal lattice yield gasses (CO2and CH4), pollen, ash, pollutantsLink between CO2and CH4concentrations and temperature changesNatural Causes of Climate Change-Plate Tectonics -Volcanic Activity-Variations in the Earth’s orbit-Solar variability* All theories can explain some portion of climate variability, but no one theory can explain all of the observed changes.8Plate TectonicsTime scale (O) millions of yearsPlate Tectonics-Distribution of Land -Growth of Ice Sheets-Change in ocean circulation9Volcanic EruptionsGasses, ashEjected into stratosphereSulfur dioxide:remains in suspensionreflects solar radiationreduce surface temperaturesMount Etna, SicilyGravity anomaly mapSite of the Chicxulubimpact, 65 million years agohttp://web.ukonline.co.uk/a.buckley/dino.htm10FREQUENCY OF IMPACTORS: Pea-size meteoroids - 10 per hour Walnut-size - 1 per hour Grapefruit-size - 1 every 10 hours Basketball-size - 1 per month 50-m rock - 1 per 100 years 1-km asteroid - 1 per 100,000 years 2-km asteroid - 1 per 500,000 years A "nemesis" parabolic comet impactor would give us only a 6-month warning. Orbital Variations: Milankovitch Cycles-eccentricity variation in the shape of Earth’s orbit-obliquity axial tilt-precession wobbleCorrelated with climate predicted by deep sea sedimentsQuaternary ice agesPredicts a cooling periodNeeds land mass near the poles to support ice sheetsNo human influence11Variations in Earth’s Orbit-Eccentricity3% difference between aphelion and perihelion20% - 30% maximumT = ~100,000 yearsVariations in Earth’s axial tilt-ObliquityDecrease tilt = decrease temperature variation between winter and summerT = ~41,000 years12Variations in Earth’s axial wobble-PrecessionControls where in the orbit seasons occurT = 23,000 - 26,000 yearsMilankovitch Cycles13Solar Variability: solar output varies through time, correlated with climate changes in Europe and North AmericaSunspots = magnetic storms 11 and 22 year cyclesδ18O record or climate change16Olighter evaporates quickertrapped in ice sheetsOrganisms during ice age are enriched in 18O14Human Impact on Global Climate Change-humans have been altering their environment since the discovery of fireIncrease in CO2and other Greenhouse GassesHuman generated aerosolsCO2Trace Gasses and Global Climate ChangeCurrent background concentration = 370 ppm15Industrial Sources of Carbon DioxideBurning of fossil fuelsDeforestation (38 m.a/y)45 – 50 % CO2remains in the atmosphereGreenhouse EffectTransparent to incoming short wave solar radiationSelective absorption of outgoing long wave radiation by gassesCO2, H2O16Increase in Atmospheric Carbon DioxideAntarctic Ice CoresMauna Loa, HI (1958)IPCC: Intergovernmental Panel on Climate Change-established by the United Nations Environmental Program-assess the state of knowledge of human-induced climate change*surface temperatures increased 0.6oC during the 20thcentury*greatest per century temperature increase in the last 1000 yrs*most of the warming over the last 50 yrs is due to human activity*Snow cover and ice extent have decreased*Eustatic sea level has risen and ocean heat content has increased17Temperature Variations since Industrial Revolution*surface temperatures increased 0.6oC during the 20thcentury*Annual temperatures compared to the (1961-1990) averageTemperature Variations (-1000 to -2000 BC)* greatest per century temperature increase in the last 1000 yrs* tree rings, ice cores, corals, historical records18Role of Trace Gasses-Methane (CH4)-Nitrous Oxide (N2O)-Chloroflorocarbons (CFCs)Nitrous Oxideenters atmosphere in agricultural regionsresidence time 150 yrsprojected to have half the green house effect of methaneMethane20-30% more effective at absorbing Infrared Radiation than CO2anaerobic bacteria in wet places (swamps, bogs, wetlands)rice paddies fields, animal guts (cattle, sheep)byproduct of oil, coal, and natural gas formationatmospheric concentration has doubled since 1800’s19http://www.ornl.gov/info/reporter/no16/methane.htmhttp://marine.usgs.gov/fact-sheets/gas-hydrates/gas-hydrates-2.gifMethane hydrate –fuel of the future or threat to life on earth?20http://www.geotimes.org/dec02/NN_hydrates.htmlMethane