Lecture 21: Global Climate Changes
• return HW#6 (to your right)
• pick up HW#4,5 (to your left)
• return trip1 on TABLE!
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
Where do Hurricanes Occur? Naming
12%
typhoons
30%
15%
hurricanes
12%
cyclones
12%
hurricanes
12%
Hurricane paths:
N hemisphere: clockw.
• most hurricanes in W. Pacific (typhoons)
S hemisphere: countercw.
• more hurricanes in E. Pacific than in Atlantic Hurricane winds:
• Indian Ocean: cyclones
N HS: ccw S HS: cw
Image: NASA’s Earth Observatory
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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 $3.2Mio Damage
Linda and Mainland
cut power to met. station on Socorro
closed resorts in Baja
flooding in mainland Mexico
15ft surge in So. Cal.
5 people swept off jetty in Newport Beach
severe flooding and mudslides in So. Cal.
(destroyed 2 houses, damaged 77)
SIO15-12:
Lecture 21: Long- and Short-term Climate Changes
http://en.wikipedia.org
S.D. Meteorological Observations
 no hurricane ever made landfall in So. Cal.
 landfall of a tropical storm in 1939
($ 2Mio damage)
 some came into SW but made landfall somewhere else
 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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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”
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
Recent Temperature and Atmospheric CO2
• T has increased nearly exponentially in last
50 years
• rate not seen in previous 950 years
• proxies: tree rings, pollen counts, etc
current CO2 changing
dramatically
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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 effect: see Lecture 15
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
Greenhouse Gases:
CO2, CH4, H2O
Radiative Forcing-Greenhouse Gases
relative ability of gas to add or reduce warming
from: Abbott “Natural Disasters”
-CO2 contribute 60%
-CH4 16% (less abundant but
more effective)
the 2most important greenhouse gases:
 natural and anthropogenic: CO2, CH4
* anthropogenic: CFC; destroys stratospheric ozone
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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)
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
Climate of the Early Earth
Venus: run-away greenhouse
Earth: moderate greenhouse
Early Earth: 98% CO2
Earth Today: 0.038%
290ºC
16ºC/61ºF
 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,
shells,
corals
as calcium
SIO15-12:fossil
Lecture
21: Longand etc.
Short-term
Climate carbonate
Changes
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!
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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!!
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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)
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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!
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
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!!
SIO15-12: Lecture 21: Long- and Short-term Climate Changes
Popquiz #10
your name and student ID
Name the three factors that
increase a hurricane surge.
(all three needed for full credit!)
SIO15-12: Lecture 21: Long- and Short-term Climate Changes