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El Ni ñ o-Southern Oscillation: Past, Present, and Future

El Ni ñ o-Southern Oscillation: Past, Present, and Future. Oceanography lecture, Kim Cobb. Why study the E l N i ñ o- S outhern O scillation? 1. It is the largest source of year-to-year global climate variability.

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El Ni ñ o-Southern Oscillation: Past, Present, and Future

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  1. El Niño-Southern Oscillation: Past, Present, and Future Oceanography lecture, Kim Cobb

  2. Why study the El Niño-Southern Oscillation? 1. It is the largest source of year-to-year global climate variability. 2. It carries negative societal consequences, both economic and humanitarian. 3. Improved forecasts minimize negative societal consequences. 4. It’s a fascinating, mysterious, and complex natural phenomenon.

  3. What is the El Niño-Southern Oscillation? A natural climate cycle in the tropical Pacific that alternates between warm (El Niño) and cold (La Niña) phases every 2-7 years. a birds-eye view of 2 of the largest El Niño events of the century: and the 2002/2003 El Niño event:

  4. This system is tightly coupled strong trade winds cool in East warm in West Average tropical Pacific conditions - trade winds blow from East to West - warm water piles up in West Pacific, driving deep atmospheric convection - cold, nutrient-rich water is brought to the surface in the East Pacific (upwelling)

  5. The Bjerknes Feedback: trade winds weaken upwelling slows Eastern Pacific warms Tropical Pacific conditions during El Niño Peruvian fisherman (1800’s): named mysterious warm, nutrient-poor waters “El Niño” Sir Gilbert Walker (1924): named East-West seesaw in sea-level pressure the “Southern-Oscillation” Jacob Bjerknes (1969): explains feedbacks that link the “El Niño” and “Southern Oscillation” phenomena http://www.pmel.noaa.gov/tao/elnino

  6. trade winds strengthen upwelling intensifies Eastern Pacific cools …and the reverse for La Niña

  7. In Oregon: ENSO influences - coho salmon spawning - agriculture - water resource management - ski conditions El Niño Impacts - the impacts are not confined to the tropical Pacific - these departures from “normal” climate carry serious economic and social costs - La Nina’s effects are roughly the opposite of El Nino’s effects - improved ENSO forecasts minimize the costs

  8. ENSO affects temperatures and rainfall in Georgia

  9. Predicting ENSO extremes 1982 El Niño 1997 El Niño El Niño La Niña Devastation caused by the 1982 El Niño made ENSO prediction a top priority for U.S. and other countries.

  10. I. Short-term Predictions 6-month prediction: - requires careful monitoring of tropical Pacific ocean + atmosphere - first ENSO model unveiled in 1987 - models predicted a weak El Nino event in 1997 The tropical Pacific observing system http://www.pmel.noaa.gov/tao/

  11. II. Long-term Predictions 1982 El Niño 1997 El Niño El Niño La Niña Are severe El Niño events becoming more frequent? How will ENSO change as the Earth warms?

  12. ENSO and Global Warming in the 21st century “This winter's El Niño gives us a taste of the extreme erratic weather that our children and grandchildren can expect more of unless we take action to reverse the trend of global warming.” then Vice President Al Gore, 1998 “Warm episodes of the El Niño-Southern Oscillation (ENSO) Phenomenon . . . have been more frequent, persistent and intense since the mid-1970s, compared with the previous 100 years.” Intergovernmental Panel on Climate Change, 2001 “Confidence in projections of changes in future frequency, amplitude, and spatial pattern of El Niño events in the tropical Pacific is tempered by some shortcomings in how well El Niño is simulated in complex models.” IPCC, 2001

  13. The instrumental record of ENSO is too short to answer some key questions: 1. Are late 20th century El Niño events more frequent and more severe than those of the recent past? 2. Is there a correlation between average global temperature and El Niño activity? 3. How much and how fast has ENSO changed in the past?

  14. Corals: The geologic record of ENSO CORALS from the tropical Pacific record ENSO in the geochemistry of their skeletons This live coral is ~50yrs old This fossil coral grew from ~1320-1390A.D. CORALS from 125 thousand years ago contain the signature of ENSO

  15. 1997 El Niño El Niño La Niña 2. ENSO only Coral reconstructions of tropical Pacific climate 1. Raw records Canals freeze in Europe “Little Ice Age” Greenland green “Medieval Warm Period” warmer 1°C colder

  16. Probing the coral record of ENSO: 1. Are late 20th century El Niño events more frequent and more severe than those of the recent past? Not necessarily. 2. Is there a clear relationship between average global temperature and El Niño activity? No. 3. How much and how fast can ENSO change? ENSO can double in strength in less than 5 years.

  17. Conclusions 1. The future of ENSO remains uncertain. 2. We have much to learn about ENSO from the geologic record. Food for Thought Coral reefs are disappearing at alarming rates worldwide, due to the combined influence of rising ocean temperatures and human disturbances (pollution, dynamite fishing, etc). Even if ENSO does not change in a “greenhouse world”, Man has perturbed the environment to the point that an El Niño event could be the “straw that breaks the camel’s back”.

  18. Web Resources This talk: http://www.gps.caltech.edu/~kcobb/osu.pdf General El Niño info: http://www.pmel.noaa.gov/tao/elnino NOVA El Niño page: http://www.pbs.org/wgbh/nova/elnino/

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