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Lecture 21: Global Climate Changes PowerPoint Presentation
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Lecture 21: Global Climate Changes
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  1. Lecture 21: Global Climate Changes • return trip1 on TABLE! • return HW#6 (to your right) • pick up HW#4,5 (to your left) office hour: Tue, Nov 20 4-5:50 pm York3030 aquarium trip 1 (HW7) last day tomorrow aquarium trip 2 (HW8) assignment is now online (and available here) midterm 2 (NOV 30) study guide will be online Nov 23

  2. Where do Hurricanes Occur? Naming typhoons 30% 12% 15% 12% hurricanes hurricanes 12% 12% cyclones Hurricane paths: N hemisphere: clockw. S hemisphere: countercw. Hurricane winds: N HS: ccw S HS: cw Image: NASA’s Earth Observatory • most hurricanes in W. Pacific (typhoons) • more hurricanes in E. Pacific than in Atlantic • Indian Ocean: cyclones

  3. Location and Frequency of Hurricanes hurricanes do not cross equator (Coriolis Effect) Image: NASA’s Earth Observatory • strongest hurricanes in W. Pacific • no hurricanes in S. Atlantic • (1 exception: hurricane Catarina, Mar 2004) • “ “ “ S.E. Pacific winds unfavorable strong cold currents

  4. El Nino and Atlantic Hurricanes Image: Abbott “Natural Disasters” • 1997 El Nino • cooler trop. Atl. • dry summers in West Africa • - less Atl. hurricanes • 1998 La Nina • warmer trop. Atl. • wet summers in West Africa • - more Atl. hurricanes

  5. Hurricanes close to home (Baja California) 1997: Cat 5 Hurricane Linda (strongest ever recorded in E.P.) • sustained winds: 185mph • gusts: 220mph • pressure: 902 mbar • no landfall but hit Socorro Island • no fatalities but $3.2Mio Damage Linda and Mainland cut power to met. station on Socorro closed resorts in Baja flooding in mainland Mexico 15ft surge in So. Cal. 5 people swept off jetty in Newport Beach severe flooding and mudslides in So. Cal. (destroyed 2 houses, damaged 77) http://en.wikipedia.org

  6. S.D. Meteorological Observations • meteorological records don’t go back very far • newspaper accounts -> Oct 2 1858 San Diego Hurricane • from winds speeds and pressure -> category 1/F2 winds • ships blown ashore • house completely destroyed • 1860 population of New San Diego county: 4325 Damage if such a hurricane would strike today: several $100Mio • no hurricane ever made landfall in So. Cal. • landfall of a tropical storm in 1939 ($ 2Mio damage) • some came into SW but made landfall somewhere else

  7. Hurricanes in Southern California? • HURRICANES • need warm water to grow/sustain • cold California Current protects us • “no hurricane has ever made landfall in SoCal” • - global warming could shift currents from: Marshak “The Earth: Portrait of a Planet”

  8. Long- and Short-term Climate Changes ….why do we have to know?... “hurricanes over Scotland; new ice age over a few weeks” ONLY IN HOLLYWOOD (2004) BUT NEVERTHELESS WORTH WATCHING

  9. Recent Temperature and Atmospheric CO2 current CO2 changing dramatically • T has increased nearly exponentially in last • 50 years • rate not seen in previous 950 years • proxies: tree rings, pollen counts, etc • Why do we care about this in a natural disasters class? • climate changes can happen rapidly (over several years) • clues of what to expect may lie in past

  10. Review: Composition of Earth’s Atmosphere Before Life Now • + other stuff • CO2 353ppm (0.0353%) • (1992); 391 ppm (2012) • - Ne 18ppm • - He 5ppm • - CH4 2ppm • - Kr 1ppm • - H2O variable (water vapor) - before life: mainly CO2 - today: mainly N2 and O2 Greenhouse Gases: CO2, CH4, H2O Greenhouse effect: see Lecture 15

  11. Radiative Forcing-Greenhouse Gases relative ability of gas to add or reduce warming • CO2 contribute 60% • CH4 16% (less abundant but • more effective) from: Abbott “Natural Disasters” • the 2most important greenhouse gases: • natural and anthropogenic: CO2, CH4 • * anthropogenic: CFC; destroys stratospheric ozone

  12. Radiative Forcing – H2O relative ability of H2O to add or reduce warming clouds: negative (reflects sunlight) AND positive (reflects IR emitted by Earth) water vapor: positive Radiative Forcing - Aerosols relative ability of substance to add or reduce warming radiative forcing of aerosols (e.g. SO2): negative in upper atmosphere positive in lower atmosphere

  13. Feedback Mechanisms feedback: secondary process that responds to and influences a change positive feedback: enhances change (e.g. warming melts ice sheets -> decrease in albedo -->> more warming) (e.g. warming thaws tundra -> release of methane -->> more warming!!) negative feedback: counteracts/moderates change (e.g. warming melts ice sheets -> cold fresh water floats on warm ocean -->> inhibits oceanic heat transport -> cooling) (e.g. warming causes more evaporation -> clouds -->> cooling)

  14. Climate of the Early Earth Early Earth: 98% CO2 290ºC Earth Today: 0.038% 16ºC/61ºF Venus: run-away greenhouse Earth: moderate greenhouse • young faint sun paradox: sun only 70% of today’s output • but 1 Ga old Earth too hot for water on Earth most CO2 is stored in limestones from chemical weathering, fossil shells, corals etc. as calcium carbonate

  15. Sun, Plate Tectonics and Climate Change • changes in solar output on scales of millions of years • early sun was fainter than today; 10% per Ga (billion years) • rifting and volcanism affect climate • spreading rates affect sea level (shallow seas) • position of continents affect climate - albedo (large continents near pole -> cooling) - arrangement of continents affect ocean circulation • INDITCATORS: • glacial striations • sedimentary rock • fossil content • - plant casts igneous rocks cannot tell past climate!

  16. Climate over Time T and Precipitation • recent long-term trend is cooling • Earth was mostly warmer than today! • glaciation very rare • colder periods tend to be drier Cretaceous: a lot warmer than today --> 3 times more CO2???? current long-term trend: COOLING

  17. Changes in Global Sea Level Sea level has changed by many 100m over time • lower sea level during glaciation • higher sea level in warm periods • sea level dropped by 200m in last 10 Mio yrs • sea level also depends on sea floor spreading!! • -> cannot infer T directly!!

  18. Short-Term Changes (1000s of years) recent short-term trend: WARMING • short-term changes NOT cause by • plate tectonics • possible causes: • Milankovich cycles • change in solar output • volcanism • ocean currents • indicators: • ice cores (CO2/oxygen isotopes) • coral rings (oxygen isotopes) • tree ring • pollen composition

  19. The Milankovitch Cycles Amount of insolation changes with Earth’s orbital parameters • eccentricity • (100,000 yrs) • tilt of spin axis/obliquity • (41,000 yrs) • precession • (25,000 yrs)

  20. The Milankovitch Cycles Earth’s orbital parameters: eccentricity, obliquity, precession - Milankovich cycles change T by up to 4oC - However: DT during ice age 5-7oC/coast and 10-13oC inland something else needed: feedback mechanisms!

  21. Milankovitch and the Positive Feedback • - saw-tooth pattern: warming happens faster than cooling • positive feedback mechanisms stronger for warming • than for cooling research done at SIO/UCSD!!

  22. Popquiz #10 your name and student ID Name the three factors that increase a hurricane surge. (all three needed for full credit!)