Transcript Climate 3

Multi-year time scale variations
• El Nino and La Nina are important
phenomena
• Occur every ~2 to 7 years when typical
ocean-atmosphere circulation breaks
down
During normal years, warm surface
waters in the Pacific lie in the east
off Indonesia
When the pattern oscillates to an
“El Nino”, the warm water shifts east
“La Nina” is characterized by colder
sea-surface temperatures and
stronger trade winds in the eastern
tropical Pacific
During “Normal Years”
Warm water in the western Pacific causes low pressure and high rainfall;
pressure system drives tradewinds from east to west;
tradewinds drive warm water to the west;
causing cold water to rise off South America and flow west.
South
America
During “El Nino”
Warm water shift to the eastern Pacific causes drought in western Pacific;
low pressure over the warm eastern Pacific causes heavy rains
and inhibits upwellings along the coast of South America.
South
America
During “El Nino”
Warm water shift to the eastern Pacific causes drought in western Pacific;
low pressure over the warm eastern Pacific causes heavy rains
and inhibits upwellings along the coast of South America.
South
America
Strong El Nino year 1982-83:
1982-83 El Nino
• Floods in Peru-Ecuador (600 fatalities)
• California flooding led to $300 million
damages
• Hurricanes in Hawaii, Tahiti
• Australia: drought and wildfires
1997-1998 El Nino Effects
La Nina hazards
• Can bring warming and low rainfall to
much of U.S.
– Can lead to fires
• Allows growth of hurricanes in Atlantic
Climate Change
2003
1958
Records of Climate Change
National Academy of Science Report, 2006
Records of Climate Change
• Historical data
• Proxy data
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Marine sediment
Ice
Coral
Lake sediment
Tree Rings
Boreholes
Glacial advance/retreat
Old glacial deposits, etc.
Oxygen isotopes
• Same atomic number (8)
• Different atomic mass
concise.britannica.com
99.63%
0.0375%
0.1995%
Delta notation
Ice data
• Influence of temperature on ice
composition
• Record of atmospheric composition
Composition of precipitation versus temperature
earthobservatory.nasa.gov
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Greenland and
Antarctic Ice
Sheet Records
>700,000 yrs
Layers counted
like tree rings
Photos: NASA
Figure 21.5A
Interpreted from Greenland ice core O-isotope data
Seafloor record
• Microfossils of
organisms in surface
and bottom water
• Limited by age of
oceanic crust (oldest
~180 my)
Source: NOAA
Influence of ice volume on Oisotope composition of seawater
Influence of ice volume on Oisotope composition of seawater
• Ice is depleted in 18O
• Residual seawater is enriched in 18O
• Positive (18O-enriched) values of
organisms indicate larger ice volume
Figure 21.4
Temperature effects
The ratio of 18O to 16O in foraminifera shells varies slightly
depending on the temperature of the surrounding water, as well the
water's salinity.
Dealing with temperature effect
• Use benthic organisms in from deep
bottom waters (relatively constant
temperature)
• Use trace element ratios tied to
precipitation temperature (e.g., Sr/Ca)
Figure 21.8
Annual growth rings in x-rayed coral (NASA)
Chapter 21 Opening Figure
Figure 21.6
Ring thickness and density a function of climate (e.g., high latitude and
altitude trees sensitive mainly to temperature)
Cross dating in
dendrochronology
Mapping glacial deposits
300 my old glacial
deposits on
Pangaea
Figure 18.32
Long term climate record
Climate Variations over Time
• Early earth: atmosphere full of CO2
• Surface would have been much hotter
because of greenhouse effect
• What changed? Much CO2 has gone into
rock form (limestones primarily)
Figure 21.5B
Interpreted from Greenland ice core O-isotope data
• Dust can be a large scale
process