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The Tropical Ocean: Limiting Global Warming?

The Tropical Ocean: Limiting Global Warming?. Nathan Banaski Senior-Physical Geography. Background-Why Do We Care?. Ocean covers more than 70% of planet Small changes in sea-surface temperatures (SST) can cause large climate changes

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The Tropical Ocean: Limiting Global Warming?

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  1. The Tropical Ocean: Limiting Global Warming? Nathan Banaski Senior-Physical Geography

  2. Background-Why Do We Care? • Ocean covers more than 70% of planet • Small changes in sea-surface temperatures (SST) can cause large climate changes • Ocean circulation plays a large role in continental climate regions • SST warming can cause breakdown in THC and abrupt climate change • First Question-whether positive feedbacks will cause runaway SST increase or negative feedbacks will balance and limit SST • Second Question-what role do ocean dynamics play in regulating SST? • The purpose of this study is to figure out whether the tropical ocean can be a thermostat and limit SST-also to prove that ocean dynamics play a large role in SST

  3. A Question of Feedbacks? • “Super Greenhouse Effect” • Positive feedback • SST rise, evaporation attempts to cool • More H2O in atmosphere • Water vapor traps more heat • SST rise more

  4. 2nd Feedback-Clouds • 2nd theory suggesting cirrus cloud negative feedback • Cirrus cloud cover over deep convective tropical areas act as thermostat • Cirrus cloud albedo high, block incoming radiation over warm pool • So, SST rise, more evaporation and convection, more cirrus cloud cover, more reflection, less radiation reaching surface, decrease SST

  5. 3rd Feedback-Evaporative Cooling Thermostat • 3rd theory suggesting evaporative cooling exceeds heat input • SST limited • As SST increase, evaporation increases • Evaporation requires energy, thus cooling ocean • As SST reach high levels, evaporative cooling will overcome positive water vapor feedback

  6. 4th Theory-”Radiation Fins” • 4th theory suggesting clouds have a net 0 effect • Clouds can reflect radiation as well as trap heat • Greenhouse trapping in deep convection areas cannot rid of energy to atmosphere • Instead-export energy to non-convective subtropics • Radiate to space

  7. Testing For Ocean Dynamics • A Zebiak-Cane model was used • Coupled ocean-atmospheric model • T˟ represents a heat flux constant that varied amongst trials • Intended to see how SST would react to varied forcing • Anomalies recorded after 4 month period and 1 year

  8. 4 Month Results 180 degrees Longitude going east between 5 N and 5 S Latitude-Smaller SST increase anomaly

  9. Between 5 degrees N and S latitude, 180 degrees longitude on eastward, SST less sensitive to forcing change • It is determined that western equatorial pacific and non-equatorial regions arebalancedby heat storage and surface flux-as forcing increases, SST increases so surface flux can balance forcing (and vice versa) • In eastern equatorial regions, forcing is balanced more through horizontal and vertical advection • So, eastern equatorial region SST changes less than surrounding areas • What does this cause???

  10. Forcing positive=Stronger easterly trade winds • East-west temp gradient increased due to eastern SST not increasing as much • (Like La Nina) • Stronger cold water upwelling in east

  11. Annual Anomalies Eastern-Equatorial SST anomalies opposite sign of forcing

  12. Cold water upwelling increasing in eastern equatorial pacific, where horizontal and vertical advection is maximum • Cold water spread to entire basin, limiting average SST! • (NINO3 Region (Eastern Equatorial Pacific: 90-150 degrees W longitude)) SST anomalies decrease as forcing increases in NINO3

  13. When forcing was reduced, NINO3 anomalies increased

  14. Summary • Many climate feedbacks exist including: Super GH effect (water vapor feedback), Cirrus cloud feedback, evaporative cooling feedback, radiator fins-each probably playing a role • But, ocean dynamics also play a role (tested by Clement, Seager, Zebiak, Cane) • Eastern-equatorial pacific less sensitive to forcing changes due to the region’s advection abilities horizontally and vertically • When forcing increases, west pacific SST rise more, temp gradient ↑, trade-winds ↑, upwelling ↑, cold water transport, limiting average SST • Thus proving that ocean dynamics play a large role in SST • Tropical ocean is like a thermostat and can limit global warming

  15. Future??? • Simple model • More to consider • If temp gradients are increased like suggested, walker and hadley circulation changes • This would cause a change possibly to the deep convective zone areas • If these areas are changed in size, radiator fin sizes are changed, which could limit or increase radiation loss to space • But, the tropical ocean thermostat will help limit sea-surface temperatures

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