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