1. Chapter 11 Climatic Change and Variability

2. Introduction Climatology considers: Climatology considers: Conditions and variabilityConditions and variability ExtremesExtremes Temporal variability can be Temporal variability can be Random (noise)Random (noise) PeriodicPeriodic TrendsTrends More permanent More permanent Step ChangeStep Change Different concepts of climate change Different concepts of climate change

3. Fig. 11.1

4. Climatic Changes in Geologic History Temperature Solar output: 25%-30% of today Solar output: 25%-30% of today Faint young sun paradox Faint young sun paradox Methanogens: Methanogens: Bacteria producing MethaneBacteria producing Methane 1 st Ice Age: 2.5 billion yrs ago 1 st Ice Age: 2.5 billion yrs ago Proterozoic EonProterozoic Eon 2 nd Ice Age: 800-600 million yrs ago 2 nd Ice Age: 800-600 million yrs ago 3 rd Ice Age: 460-430 million yrs ago 3 rd Ice Age: 460-430 million yrs ago

5. Geologic Time Scale Fig. 11.2

6. Current Ice Age may have begun 40-50 million yrs ago Current Ice Age may have begun 40-50 million yrs ago Glacial phases (ice advances)Glacial phases (ice advances) 50K-150 K yrs50K-150 K yrs Holocene Interglacial Phase (ice retreats) Holocene Interglacial Phase (ice retreats) Current (began 9000 yrs ago)Current (began 9000 yrs ago) Wisconsin Glacial Phase Wisconsin Glacial Phase 18K yrs ago18K yrs ago Table 11.1: Interglacial Phases in Pleistocene Ice Age

7. Ice Ages and Sea Level Ice Ages Ice Ages Sea level decreasesSea level decreases Coastline 20,000 yrs ago East Antarctic Ice Sheet Melted (170 ft) West Antarctic Ice Sheet Melted (22 ft)

8. Effect of 6 m Sea Level Rise Fig. 11.4

9. Recent Trends Younger Dryas Younger Dryas Cold period 13K – 11.5K yrs agoCold period 13K – 11.5K yrs ago Hypsithermal Hypsithermal Warmer period 8K-5K yrs agoWarmer period 8K-5K yrs ago Dark Ages Dark Ages Colder period 500 AD - 900ADColder period 500 AD - 900AD Medieval Warm Period Medieval Warm Period 900 AD – 1450 AD900 AD – 1450 AD Little Ice Age Little Ice Age 1450-18501450-1850

10. Fig. 11.5

11. How Do We Know What We Know about Past Climatic Changes? Formal meteorological records Formal meteorological records Mid – late 1800’sMid – late 1800’s Radiosondes Radiosondes Mid 1900sMid 1900s Satellite temperature data Satellite temperature data 1970s1970s

12. Radiometric Dating Used to determine approximate time Used to determine approximate time Radioactive Decay Radioactive Decay Rate at which spontaneous nuclear disintegration of isotopes occurRate at which spontaneous nuclear disintegration of isotopes occur

13. Lithospheric and Cryospheric Evidence Fig. 11.6 and 11.7 Grand Canyon Grand Canyon Evidence of alternating periods of above and below oceanEvidence of alternating periods of above and below ocean Glacial erratics Glacial erratics Provide clues that glaciations occurred in pastProvide clues that glaciations occurred in past Glacier advanceGlacier advance Equatorward or Poleward Equatorward or Poleward Ice cores Ice cores O 18O 18 More in warm periods More in warm periods Evaporates easier in warm periods Evaporates easier in warm periods

14. Biological Evidence Fossils Fossils Foraminifera: Marine protozoansForaminifera: Marine protozoans Oxygen isotopesOxygen isotopes Palynology Palynology Study of pollen and sporesStudy of pollen and spores DifficultDifficult Different plant species produce different amount of pollen/spores Different plant species produce different amount of pollen/spores Dendrochronology Dendrochronology Tree RingsTree Rings Tell Climate StressTell Climate Stress Others Others Calcium Carbonate produced by exoskeletonCalcium Carbonate produced by exoskeleton Ocean temperature clues Ocean temperature clues TreelinesTreelines

15. Historical Data Diaries Diaries Ship logs Ship logs Newspaper accounts Newspaper accounts Problems: Problems: Difficult to quantifyDifficult to quantify

16. Natural Causes of Climatic Change and Variability Geological Geological Astronomical Astronomical Solar Solar Oceanographic Oceanographic

17. Continental Drift and Landforms Fig. 11.8 Continent position has been used to explain Ice age/non Ice age Continent position has been used to explain Ice age/non Ice age Affects ocean currents Affects ocean currents Bering Strait nearly cuts off water Bering Strait nearly cuts off water Ice more likely to formIce more likely to form Mountains Mountains Affect weather patternsAffect weather patterns

18. Milankovitch Cycles Eccentricity Eccentricity Tilt Tilt Precession Precession

19. Eccentricity Fig. 11.9 Circularity of orbit around the sun Circularity of orbit around the sun Periodicity Periodicity 95,000 yrs95,000 yrs 0%-11% Perihelion difference0%-11% Perihelion difference Presently low eccentricity (3%) Presently low eccentricity (3%) Low eccentricity Low eccentricity Glacial periodsGlacial periods High eccentricity High eccentricity Interglacial periodsInterglacial periods

20. Tilt Fig. 11.10 Changes from 21.8°-24.4° Changes from 21.8°-24.4° Periodicity Periodicity 44,000 yrs44,000 yrs Low angle Low angle Less variabilityLess variability High angle High angle More variabilityMore variability

21. Precession Fig. 11.11 Wobble of the earth’s axis Wobble of the earth’s axis Periodicity Periodicity 23,000 yrs23,000 yrs 11,500 yrs 11,500 yrs Perihelion in JulyPerihelion in July Aphelion in JanAphelion in Jan

22. Combined Effects When all 3 in phase When all 3 in phase Amplifies Glacial/Interglacial periodsAmplifies Glacial/Interglacial periods

23. Volcanic Activity Fig. 11.12 Atmospheric CO 2 formed on long time scales Atmospheric CO 2 formed on long time scales Dust, debris produced on short time scales Dust, debris produced on short time scales Barringer Crater created by meteor impact near Winslow, AZ Barringer Crater created by meteor impact near Winslow, AZ Proof of short term dust related cooling 50K yrs agoProof of short term dust related cooling 50K yrs ago

24. Variations in Solar Output Sunspots – more output Sunspots – more output Max sunspots every 11 yrs Max sunspots every 11 yrs Magnetic field changes every 22 yrs Magnetic field changes every 22 yrs Correlation between 22 yr climate events Correlation between 22 yr climate events

25. Number of Sunspots since Maunder Minimum (Fig. 11.13)

26. ENSO Events Fig. 11.14 Monsoon circulations weaken Monsoon circulations weaken Atlantic hurricane activity weakens Atlantic hurricane activity weakens 3-7 yrs 3-7 yrs Frequency changing? Frequency changing?