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

SouthAmerica

During “Normal Years”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.

SouthAmerica

During “El Nino”During “El Nino”

Warm water shift to the eastern Pacific causes drought in western Pacific;low pressure over the warm eastern Pacific causes heavy rainsand inhibits upwellings along the coast of South America.

SouthAmerica

During “El Nino”During “El Nino”

Warm water shift to the eastern Pacific causes drought in western Pacific;low pressure over the warm eastern Pacific causes heavy rainsand inhibits upwellings along the coast of 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

19582003

Climate Change

Records of Climate ChangeRecords of Climate Change

National Academy of Science Report, 2006

Records of Climate Change

• Historical data • Proxy data

– 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

99.63% 0.0375% 0.1995%concise.britannica.com

Delta notation

Ice data

• Influence of temperature on ice composition

• Record of atmospheric composition

earthobservatory.nasa.govComposition of precipitation versus temperature

Greenland and Antarctic Ice Sheet Records

>700,000 yrs Layers counted

like tree rings

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 O-isotope composition of seawater

• Ice is depleted in 18O

• Residual seawater is enriched in 18O

• Positive (18O-enriched) values of organisms indicate larger ice volume

Influence of ice volume on O-isotope composition of seawater

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

Figure 18.32300 my old glacial deposits on Pangaea

Long term climate recordLong 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