Week 15 NotesTONIGHTTONIGHT (May 5) (May 5)

• Term Papers DueTerm Papers Due• Climate Change (Chp 14)Climate Change (Chp 14)• ReviewReview

May 12 – Class begins at 6:30 PMMay 12 – Class begins at 6:30 PM• Final Exam Final Exam • Extra Credit papers dueExtra Credit papers due

May 18 (Mon) - Grades availableMay 18 (Mon) - Grades available• Email: jnull@ggweather.comEmail: jnull@ggweather.com

Final ExamFinal Exam• 200 Points200 Points

• 66 multiple choice questions (3 points 66 multiple choice questions (3 points each)each)

• ~ 22 questions from~ 22 questions from• Thunderstorms (Chp 10)Thunderstorms (Chp 10)• Tropical Storm (Chp 11)Tropical Storm (Chp 11)• Air Pollution (Chp 12)Air Pollution (Chp 12)• Climate Classifications (Chp 13) Climate Classifications (Chp 13) • Climate Change (Chp 14) Climate Change (Chp 14)

• ~ 44 questions - previous chapters~ 44 questions - previous chapters• Study previous exams !!Study previous exams !!

ClimateClimateChangeChange

Climate Change vs. Climate VariabilityClimate Change vs. Climate Variability

• Climate variability:Climate variability:– Average value of a climate element Average value of a climate element

(temperature) does not change, but fluctuates (temperature) does not change, but fluctuates from observation to observationfrom observation to observation

• Climate change:Climate change:– Average value of the climate element changes Average value of the climate element changes

over time (average temperature increasing or over time (average temperature increasing or decreasing)decreasing)

Climate ChangeClimate Change• Climate change is complicatedClimate change is complicated• Change impacts some areas more than othersChange impacts some areas more than others• Human perspective is relativeHuman perspective is relative

- short lifetimes- short lifetimes• GCMs (Global Climate Models) may produce more GCMs (Global Climate Models) may produce more

than one outcome in the climate systemthan one outcome in the climate system• Recent realization that humans DO impact climateRecent realization that humans DO impact climate

Looking into the PastLooking into the Past• Use caution – Use caution –

• Alternative explanations other than climate change!Alternative explanations other than climate change!• In 17th & 18th centuries, the river Thames in London froze in In 17th & 18th centuries, the river Thames in London froze in

winterwinter• Much colder winters?Much colder winters?• Or another explanation: River was able to freeze more Or another explanation: River was able to freeze more

readily back then?readily back then?– Old London bridge acted to slow river flow downOld London bridge acted to slow river flow down– Lack of embankments back then (river wider)Lack of embankments back then (river wider)– Lack of waste heat from industrial plantsLack of waste heat from industrial plants

• Weather records show winters back then were 1º C coolerWeather records show winters back then were 1º C cooler

Reconstructing Past ClimatesReconstructing Past Climates

• Instruments records Instruments records • Proxy measurementsProxy measurements

• Tree ringsTree rings• Ice coresIce cores

• Plate tectonics (folding, faulting) and erosion Plate tectonics (folding, faulting) and erosion complicates the picturecomplicates the picture– Much of the record is confused or destroyed (90-99% Much of the record is confused or destroyed (90-99%

eroded)eroded)– Little remains from first 90% of Earth’s lifetimeLittle remains from first 90% of Earth’s lifetime• Changes in arrangement of continents and oceansChanges in arrangement of continents and oceans

Ice AgeIce Age• Times in Earth’s history when ice covered a large part Times in Earth’s history when ice covered a large part

of the Earth’s surfaceof the Earth’s surface• First proposed by Swiss naturalist Louis AgassizFirst proposed by Swiss naturalist Louis Agassiz

• ““Erratics” – rocks found in unusual areasErratics” – rocks found in unusual areas• Found blocks of granite transported 100 kilometers Found blocks of granite transported 100 kilometers

from Alps from Alps

From 2.7 to 1.8 Billion Years AgoFrom 2.7 to 1.8 Billion Years Ago• ““Snowball Earth”: Widespread, global glaciationSnowball Earth”: Widespread, global glaciation• Evidence of glaciers in parts of Africa located Evidence of glaciers in parts of Africa located

near the Equator at the timenear the Equator at the time• 3 discrete glaciations found in Wyoming 3 discrete glaciations found in Wyoming

between 2.5 and 2.2 billion years agobetween 2.5 and 2.2 billion years ago

Sudden Shift in ClimateSudden Shift in Climate• Catastrophic Catastrophic event caused increase in COevent caused increase in CO22

• Earth remained free of ice caps for 1 billion Earth remained free of ice caps for 1 billion yearsyears

• Snowball Earth appeared again – several ice Snowball Earth appeared again – several ice ages observed following warm-upages observed following warm-up

• ““Cambrian explosion” – after last ice age in Cambrian explosion” – after last ice age in this period, acceleration in evolution observedthis period, acceleration in evolution observed

The Big FiveThe Big Five

• Five clearly established events of mass Five clearly established events of mass extinctionextinction

• During last 600 million years, 99.9% of all During last 600 million years, 99.9% of all previous species diedprevious species died

• Now: 1 million species, 75% insectsNow: 1 million species, 75% insects

100 Million Years Ago100 Million Years Ago

• Warmest climate period supported by proxy Warmest climate period supported by proxy datadata

• 6º C to 12º C warmer than present day6º C to 12º C warmer than present day• Configuration of continents played a roleConfiguration of continents played a role

– Equatorial seawayEquatorial seaway

• TodayToday– Circumpolar ocean current around Antarctica Circumpolar ocean current around Antarctica

makes Antarctica colder than the Arcticmakes Antarctica colder than the Arctic

End of the MesozoicEnd of the Mesozoic

• 248 to 65 Million Years Ago248 to 65 Million Years Ago• Sudden cooling observedSudden cooling observed• One of the “Big Five”One of the “Big Five”• Dinosaurs extinctDinosaurs extinct

PleistocenePleistocene• 1.8 million to ~10,000 years ago1.8 million to ~10,000 years ago• Repeated ice ages – 32% of Earth covered by Repeated ice ages – 32% of Earth covered by

iceice– Evidence of 7 glacial periodsEvidence of 7 glacial periods– Each glacial period occurs every 100,000 yearsEach glacial period occurs every 100,000 years– Each glacial period had substantial fluctuations in climate – Each glacial period had substantial fluctuations in climate –

from extreme cold to near interglacial warmth.from extreme cold to near interglacial warmth.• Fluctuation in climate dominated by cycles of 21,000, Fluctuation in climate dominated by cycles of 21,000,

41,000, and 100,000 years. 41,000, and 100,000 years.• From sediment/ice core data – changes can be From sediment/ice core data – changes can be

sudden!sudden!

End of PleistoceneEnd of Pleistocene• Last ice age maxed out about 18,000 years agoLast ice age maxed out about 18,000 years ago

– Ice sheet 3 kilometers thick as far south as Great LakesIce sheet 3 kilometers thick as far south as Great Lakes– Total ice volume of ~ 90,000,000 km3 (30 million today)Total ice volume of ~ 90,000,000 km3 (30 million today)– Sea level lower by 90-120 metersSea level lower by 90-120 meters– Global average temperatures 5º C colder than nowGlobal average temperatures 5º C colder than now

• Dramatic warming started 15,000 years agoDramatic warming started 15,000 years ago• Rapid change in circulation pattern seen (dust)Rapid change in circulation pattern seen (dust)• Conclusion: Climate is capable of sudden, large Conclusion: Climate is capable of sudden, large

shiftsshifts

PleistocenePleistocene

The HoloceneThe Holocene

• Recent 10,000 yearsRecent 10,000 years• Warm, stable interglacial periodWarm, stable interglacial period• Extraordinary quiet phase compared to earlier Extraordinary quiet phase compared to earlier

eraseras

6,000 Years Ago6,000 Years Ago

• Laurentide ice sheet disappearedLaurentide ice sheet disappeared• Peak in post-glacial warmingPeak in post-glacial warming• Temperatures 2-3º C warmer than nowTemperatures 2-3º C warmer than now• Ancient trees found farther north than Ancient trees found farther north than

trees exist todaytrees exist today

5,500 Years Ago5,500 Years Ago

• Cooler and Drier conditionsCooler and Drier conditions• Historical records can be used nowHistorical records can be used now• Desiccation of Sahara – decline in rain Desiccation of Sahara – decline in rain

4,000 years ago4,000 years ago• Tree line retreats southwardTree line retreats southward• Mountain glaciers growingMountain glaciers growing

99thth and 10 and 10thth Centuries Centuries• Warming in Europe and North AtlanticWarming in Europe and North Atlantic• Vikings settle GreenlandVikings settle Greenland• Limited geographical coverage of records Limited geographical coverage of records

makes it difficult to say global climate was makes it difficult to say global climate was warmerwarmer

1616thth to 19 to 19thth Centuries Centuries• Cooler period –”Little Ice Age”Cooler period –”Little Ice Age”

– Firmer foundation of evidenceFirmer foundation of evidence– Best known example of climate variability in Best known example of climate variability in

recorded historyrecorded history– Glaciers expandedGlaciers expanded– Cool summers, severe wintersCool summers, severe winters– Not a period of sustained coldNot a period of sustained cold– Concentrated in winter halfConcentrated in winter half

Since Late-19Since Late-19thth Century Century

• Global warmingGlobal warming• Evidence comes primarily from instrumentsEvidence comes primarily from instruments• Annual global temperatures have risen 0.62º CAnnual global temperatures have risen 0.62º C• Warmest years in the record have all fallen in 1990sWarmest years in the record have all fallen in 1990s• Warmest 20-year periods: 1925-1944, 1978-1997Warmest 20-year periods: 1925-1944, 1978-1997• Slight cooling in-between these yearsSlight cooling in-between these years

Climate System Components

Climate Change BackgroundClimate Change Background The earth has been in a warming trend for the The earth has been in a warming trend for the

past few centuriespast few centuries Mainly due to the increase in greenhouse gas Mainly due to the increase in greenhouse gas

emissions emissions COCO22, CH, CH44, N, N22O, HO, H22OO

Atmosphere warmer because it can retain Atmosphere warmer because it can retain more heat (larger greenhouse effect)more heat (larger greenhouse effect)

The Greenhouse EffectThe Greenhouse Effect

• Greenhouse gases:– Greenhouse gases are transparent to incoming Greenhouse gases are transparent to incoming

solar radiation (short wave) radiation, but absorb solar radiation (short wave) radiation, but absorb outgoing long-wave radiation.outgoing long-wave radiation.

• Greenhouse gases act to warm the atmosphere• The most abundant greenhouse gas is water vapor.

The Enhanced “Runaway”The Enhanced “Runaway”Greenhouse EffectGreenhouse Effect

• Burning of fossil fuels increases greenhouse gas concentrations– Fossil fuels are coal, petroleum, natural gas

• Clearing of forests– Increases CO2 because plants remove CO2 from

the air

• Enhanced greenhouse gases lead to a warmer climate.

Current CO2: ~380 ppm

Greenhouse GasesGreenhouse Gases

Greenhouse Gases Warming EffectivenessGreenhouse Gases Warming Effectiveness• Different gases vary in their ability to act as a Different gases vary in their ability to act as a

greenhouse warmer.greenhouse warmer.GasGas Concentration (ppm)Concentration (ppm) Greenhouse Greenhouse

Warming Warming Strength Strength ((WW/m/m-2-2))

Water VaporWater Vapor 30003000 ~100~100Carbon DioxideCarbon Dioxide 353353 ~50~50MethaneMethane 1.721.72 1.71.7Nitrous oxideNitrous oxide 0.310.31 1.31.3

Recent WarmingRecent Warming• Primarily a decrease in exceptionally cold Primarily a decrease in exceptionally cold

temperaturestemperatures• Also increases in exceptionally warm temperaturesAlso increases in exceptionally warm temperatures

– Night minimum temperatures have increased more rapidly Night minimum temperatures have increased more rapidly than daytime maximum temperaturesthan daytime maximum temperatures

• Diurnal temperature range has decreased 0.08º C Diurnal temperature range has decreased 0.08º C per decadeper decade

• Most pronounced warming – northern continentsMost pronounced warming – northern continents• Marked coolingMarked cooling

– NW Atlantic OceanNW Atlantic Ocean– Less in north central PacificLess in north central Pacific

• Changes appear most clearly in winterChanges appear most clearly in winter

Recent WarmingRecent Warming

Mt. Pinatubo - Global Cooling1991 - Changing forcing changes the temperature (and water vapor, etc.)

Warming Measurements

Future projections of COFuture projections of CO22 ConcentrationsConcentrations

• What happens in the future depends on how much more What happens in the future depends on how much more COCO22 we release into the atmosphere we release into the atmosphere

• Even the low-emission scenarios result in greatly Even the low-emission scenarios result in greatly increased COincreased CO22 concentrations by the year 2100 concentrations by the year 2100

– Current Concentration: 380 ppmCurrent Concentration: 380 ppm– Max scenario: 970 ppmMax scenario: 970 ppm– Min scenario: 550 ppmMin scenario: 550 ppm

Future Temperature ProjectionsFuture Temperature Projections

GCM ForecastsGCM Forecasts

Notes on Temperature ProjectionsNotes on Temperature Projections

• Projected Warming (2000 – 2100)Projected Warming (2000 – 2100)– From ~2.5From ~2.5°F to ~10.5°F°F to ~10.5°F– Not all places will warm at the same rateNot all places will warm at the same rate

• Curves represent seven independent scenariosCurves represent seven independent scenarios• Each bar on right represent range of warming Each bar on right represent range of warming

produced by models of differing sensitivities for a produced by models of differing sensitivities for a specific scenario.specific scenario.

Potential Climate Change ImpactsPotential Climate Change Impacts

““Median” Scenario Temperature ProjectionsMedian” Scenario Temperature Projections• Land areas projected to warm more than oceansLand areas projected to warm more than oceans• Greater warming at high latitudesGreater warming at high latitudes

Some areas are projected to become wetter, others Some areas are projected to become wetter, others drier with an overall increase projecteddrier with an overall increase projected

Annual mean precipitation change: 2071 to 2100 Relative to 1990

““Median” Scenario Precipitation ProjectionsMedian” Scenario Precipitation Projections

Sea Level ProjectionsSea Level Projections

Main Climate Change SummaryMain Climate Change Summary• Higher temperatures – Higher temperatures –

• Especially on landEspecially on land• Polar RegionsPolar Regions

• Hydrological cycle more intenseHydrological cycle more intense• Storms have more “fuel,” so they can be more Storms have more “fuel,” so they can be more

powerful, bringing more intense rainfalls powerful, bringing more intense rainfalls • Sea levels riseSea levels rise

• Oceans expand with extra heatOceans expand with extra heat

• Melting of polar iceMelting of polar ice

Other Possible ChangesOther Possible Changes• As Poles warm quickly relative to the tropics…As Poles warm quickly relative to the tropics…

– The jet stream will weaken and move northThe jet stream will weaken and move north• The storm track will also move northThe storm track will also move north• Latitude bands 30-40 degrees should get drierLatitude bands 30-40 degrees should get drier• Rain events begin to replace snow eventsRain events begin to replace snow events• Reduction in the # of strong tornadoes in U.S.Reduction in the # of strong tornadoes in U.S.• Tornado Alley migrates northTornado Alley migrates north• Atlantic hurricanes will more easily form and be Atlantic hurricanes will more easily form and be

generally strongergenerally stronger

Predictions For the Bay AreaPredictions For the Bay Area

• Decreased winter precipitation as jet stream moves Decreased winter precipitation as jet stream moves northnorth

• Increased summer precipitation as water is Increased summer precipitation as water is warmer/more subtropical moisturewarmer/more subtropical moisture

• Weaker sea breezes due to warmer ocean Weaker sea breezes due to warmer ocean temperatures results in hotter summerstemperatures results in hotter summers

• Less snowpack in Sierra Nevada, leading to water Less snowpack in Sierra Nevada, leading to water shortagesshortages

Feedback MechanismsFeedback Mechanisms

• Climate is linked with many physical processesClimate is linked with many physical processes– A change in part of the climate system may cause A change in part of the climate system may cause

subsequent changes in other partssubsequent changes in other parts– Subsequent changes could support or act against Subsequent changes could support or act against

the original changethe original change

Positive FeedbackPositive Feedback• When the response in a second variable reinforces the

change in the initial variable• Example of positive feedback:

– Global temperatures increase– Increase in temperature melts the ice and snow in

the upper latitudes– Loss of ice and snow results in a lower albedo at the

surface in the upper latitudes– Lower albedo leads to less reflection and more

insolation– More insolation results in warmer temperatures

Negative FeedbackNegative Feedback• When the response in a second variable lessens the When the response in a second variable lessens the

change caused by the initial variablechange caused by the initial variable• Example of negative feedback:Example of negative feedback:

– Global warming leads to more atmospheric water Global warming leads to more atmospheric water vaporvapor

– Increased water vapor leads to increased cloud coverIncreased water vapor leads to increased cloud cover– Increased cloud cover leads to a higher albedoIncreased cloud cover leads to a higher albedo– Higher albedo results in less insolation at the surfaceHigher albedo results in less insolation at the surface– Reduced insolation at the surface leads to coolingReduced insolation at the surface leads to cooling

Week 15 NotesOut of fairness, I have decided to Out of fairness, I have decided to

give a general 24-hour extension to give a general 24-hour extension to ALL students on their term papers. ALL students on their term papers.

The very latest I will accept any The very latest I will accept any paper is at 6 PM tomorrow (5/6) paper is at 6 PM tomorrow (5/6)

evening via email only. No evening via email only. No exceptions.exceptions.