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Presented by Andrew Wittenberg Geophysical Fluid Dynamics Laboratory 17 October 2012

Tropical Climate Change and ENSO. Presented by Andrew Wittenberg Geophysical Fluid Dynamics Laboratory 17 October 2012. NOAA GOES-11 5 Oct 2011 1800 UTC. The Tropics: Firebox of the global circulation. Thompson Higher Education. 2. Projected surface temperature changes.

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Presented by Andrew Wittenberg Geophysical Fluid Dynamics Laboratory 17 October 2012

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  1. Tropical Climate Change and ENSO Presented by Andrew Wittenberg Geophysical Fluid Dynamics Laboratory 17 October 2012 NOAA GOES-11 5 Oct 2011 1800 UTC

  2. The Tropics: Firebox of the global circulation Thompson Higher Education 2

  3. Projected surface temperature changes Vecchi et al. (2008) Vecchi & Wittenberg (2010) Collins et al. (2010) Xie et al. (2010) Strongest warming over land & equatorial Pacific More warming in calm areas, and where winds weaken Feedbacks from low clouds & ocean advection 3

  4. Projected water vapor changes Vecchi & Wittenberg (2010) Collins et al. (2010) Xie et al. (2010) Tropics today: ~40 kg of water vapor 2050: +4 kg Warming pumps water vapor into the atmosphere 4

  5. Projected rainfall changes Held & Soden (2006) Vecchi & Wittenberg (2010) DiNezio et al. (2010) Xie et al. (2010) Broadly: “the wet get wetter, the dry get drier”. Over tropical oceans: “the warmer get wetter”. 5

  6. Projected tropospheric temperature changes Held & Soden (2006) Vecchi et al. (2006) Frierson et al. (2007) Collins et al. (2010) Increased static stability of atmosphere Helps expand Hadley Cell Weakens convective mass fluxes & trade winds 6

  7. Projected upper-ocean temperature changes DiNezio et al. (JC 2009, EOS 2010) Collins et al. (2010) Tropical ocean more stratified Stronger, shallower, and flatter equatorial thermocline 7

  8. Earth's dominant interannual climate fluctuation Normal El Niño NOAA/CPC 8

  9. Projected ENSO changes (CMIP3/AR4) Weak/ambiguous near-term anthropogenic impacts on ENSO Intrinsic modulation Reviews: Meehl et al. (IPCC-AR4 2007) Guilyardi et al. (BAMS 2009) Vecchi & Wittenberg (WIREs CC 2010) Collins et al. (Nature Geosci. 2010) CM2.1 std(SLP.PC1 of SRES.A2 (2051-2100)) / std(SLP.PC1 of 20C3M) 30S-30N, 30E-60W van Oldenborgh et al. (OS 2005) correl(SST trend of 1%/yr, SST.PC1 of PICTRL) 10S-10N, 120E-80W Yamaguchi & Noda (JMSJ 2006) 9

  10. Intrinsic modulation of ENSO: Observed Vecchi & Wittenberg (WIREs CC 2010) Historical SSTA (ERSST.v3) Palmyra corals (Cobb et al., Nature 2003) Multiproxy reconstructions: Emile-Geay et al. (2011abc, subm.) 10

  11. Intrinsic modulation of ENSO: Simulated Wittenberg (GRL 2009) 11

  12. The most extreme ENSO epochs Wittenberg et al. (in prep.) 12

  13. Initial conditions for “perfect” reforecasts Wittenberg et al. (in prep.) 13

  14. 40 “perfect” reforecasts – best possible skill Wittenberg et al. (in prep.) 14

  15. 286 ppmv 1860: Spread of 100yr NINO3 SST spectra Wittenberg (2009) 15

  16. 353 ppmv 1990: Stronger annual cycle & ENSO Wittenberg (2009) 16

  17. 2xCO2: A perfect climate for ENSO? 572 ppmv Wittenberg (2009) 17

  18. 4xCO2: Stronger annual cycle, weaker ENSO 1144 ppmv Wittenberg (2009) 18

  19. Competing changes in ENSO feedbacks 1. Amplifiers - stronger rainfall & wind stress responses to SSTAs - stronger thermocline, shallower mixed layer - weaker replenishment of surface waters from below2. Dampers - stronger evaporative & cloud-shading responses - weaker upwelling -> surface less connected to thermocline - smaller dynamic warm pool -> less room for warming3. Ambiguous effects - stronger intraseasonal wind variability Guilyardi et al. (BAMS 2009); Vecchi & Wittenberg (WIREs CC 2010) Collins et al. (Nature Geosci. 2010); DiNezio et al. (JC 2009; EOS 2010; JC 2011 subm.) Ongoing activities with CLIVAR Working Groups, D. Battisti, A. Atwood, M. Cane, C. Karamperidou, F.-F. Jin, J. Brown, F. Graham 19

  20. Summary 1. Projections of tropical climate change - tropics moisten, stratify, expand - circulation weakens; ocean thermocline shoals & flattens - SST: calm(er) get warmer; ocean advection changes - rainfall: wet get wetter; warmer get wetter - distinct from El Niño2. Is ENSO changing? - diverse projections - competing feedbacks + optima + model biases -> uncertainty3. Risk of intrinsic ENSO modulation - ENSO capable of wide swings in behavior on its own - interannual predictability only, except after a big event 20

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