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Is the AMO a Natural Climate Mode and How Does it Affect Hurricanes?

Relevant publication:. Enfield, D.B., and L. Cid-Serrano, 2007: Secular and multidecadal warmings in the North Atlantic and their relationships with major hurricanes. Journal of Climate, submitted . Is the AMO a Natural Climate Mode and How Does it Affect Hurricanes?. David Enfield

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Is the AMO a Natural Climate Mode and How Does it Affect Hurricanes?

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  1. Relevant publication: Enfield, D.B., and L. Cid-Serrano, 2007: Secular and multidecadal warmings in the North Atlantic and their relationships with major hurricanes. Journal of Climate, submitted. Is the AMO a Natural Climate Mode and How Does it Affect Hurricanes? David Enfield NOAA Atlantic Oceanographic & Meteorological Lab Miami, Florida Luis Cid-Serrano Dept. Statistics, Universidad de Concepción, Chile NOAA Atlantic Oceanographic & Meteorological Laboratory

  2. In this talk, we shall …. … review and assess recent arguments to the effect that the AMO is negligible or anthropogenically forced, … review contrary evidence from paleoclimate and models that AMO is a natural climate mode, … discuss the Atlantic warm pool (AWP) and its impact on hurricanes, … introduce a simple scheme for separating secular and multidecadal variability in long SST time series, … assess the relative impact of secular & multidecadal components of NA-SST on the AWP, … discuss what this may mean for the future. NOAA Atlantic Oceanographic & Meteorological Laboratory

  3. … A multidecadal oscillation of SST found mainly in the North Atlantic — the Atlantic multidecadal oscillation (AMO)

  4.   Global warming model w/ greenhouse gases & solar forcing (red) • …residual fluctuations (blue) not explained by GHGs (red) • …implies that residual reflects natural fluctuations in SST NOAA Atlantic Oceanographic & Meteorological Laboratory

  5. Correlation of AMO vs. July-September rainfall NOAA Atlantic Oceanographic & Meteorological Laboratory

  6. Warm Atlantic • 1953-1970 & 1995-2000 ==> 25 years of AMO warm phase. • 33 major hurricanes and frequent US landfalling hurricanes. • Now: Windstorm insurance skyrockets. Wide public consciousness of the AMO-related shift in risk. Cool Atlantic Goldenberg et al. (Science, 2001) • 1971-1994 ==> 25 years of AMO cool phase. • Only 15 major hurricanes and US landfalling hurricanes are infrequent. • Then: Windstorm insurance is cheap. Underwriters and actuaries are unaware of climate risk shifts. NOAA Atlantic Oceanographic & Meteorological Laboratory

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  10. Gray et al. (2004) AMO reconstruction Eastern US and European tree rings have been “calibrated” to give an extended 425-year index of the AMO. The extended AMO proxy (b) correlates highly with the instumental index (a) and allows us to identify long and short regime intervals of the AMO (c). Strong evidence that the AMO is a natural climate mode, not anthropogenic. NOAA Atlantic Oceanographic & Meteorological Laboratory

  11. Enfield & Cid (2006) regime interval analysis Gamma (A,B) distribution fit to proxy interval distributions with Monte Carlo resampling (spectral randomization) We repeat the Monte Carlo re-samplings for shorter 141-year data segments A, B for 20th century are within the range for the past proxy data - consistent with 20th century being natural NOAA Atlantic Oceanographic & Meteorological Laboratory

  12. Coupled GCMs with a dynamical ocean & without external foring suggest that the engine for the AMO involves the Atlantic Meridional Overturning Circulation          (A-MOC) …References: Delworth (1993)Delworth and Mann (2000)Latif et al. (2004)Knight et al. (GRL, 2005) The A-MOC mechanism is also consistent with observations …Reference: Dima & Lohmann (2006) AMO <==> Overturning circulation (A-MOC) NOAA Atlantic Oceanographic & Meteorological Laboratory

  13. Of the 18 years with small warm pools 3 busy years, 23 storms Of the 18 years with large warm pools 11 busy years, 82 storms 54 Years of Atlantic Hurricanes (1950-2003) Busy hurricane years = years for which the number of late-season hurricanes fall within the top tercile of all years NOAA Atlantic Oceanographic & Meteorological Laboratory

  14. How is the NCAR AGCM (CAM 3.1) affected if the summer (ASO) Atlantic warm pool (AWP) is suppressed?(Wang et al. 2006) ==> Vertical wind shear is decreased by 36% (5 m/sec) NOAA Atlantic Oceanographic & Meteorological Laboratory

  15. The impact of the summer AWP is to increase the convective available potential energy (CAPE) The impact of greater vertical wind shear and CAPE is to favor deep convection & major hurricanes, as observed NOAA Atlantic Oceanographic & Meteorological Laboratory

  16. Nonlinear Decompostition of NA-SSTLeast-squares fit ==>T(t) = 0 + 2 t2 NOAA Atlantic Oceanographic & Meteorological Laboratory

  17. How are secular & multidecadal changes distributed? For 1975-2000 T = +0.14 °C Over MDR (ASO) For 1975-2000 T = +0.37 °C Over MDR (ASO) NOAA Atlantic Oceanographic & Meteorological Laboratory

  18. Impact of 1975-2000 warming on Atlantic Warm Pool Secular increase T = +0.14 °C 1975 area ==> +14% Multidecadal T = +0.37 °C 1975 area ==> +36% Total warming T = +0.51 °C 1975 area ==> +54% NOAA Atlantic Oceanographic & Meteorological Laboratory

  19. IPCC multi-model ensemble IPCC 4th Assessment projection for 2011-2030 surface temperatures relative to 1980-1999 (multi-model ensemble, three emission scenarios -- B1, A1B and A2). 0.6 x IPCC Future TSFC warming TNA(2000-2025) ~ +0.25 ±0.10 °C Future NA-SST (quadratic) TNA(2000-2025) ~ +0.2 °C ==> We may never see 1975 major hurricane activity levels again, but possibly some easing from present levels NOAA Atlantic Oceanographic & Meteorological Laboratory

  20. Impact of 1975-2025 warming on Atlantic Warm Pool 1975 => 2000 warming T = +0.51 °C 1975 area +54% => 2025 with AMO reversal T = .51+.25-.37 = +0.39 °C 1975 area ==> +38% => 2025 without AMO rev. T = .51+.25 = +0.76 °C 1975 area ==> +84% NOAA Atlantic Oceanographic & Meteorological Laboratory

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  22. References: Andronova, N. G. and M. E. Schlesinger, 2000: Causes of global temperature changes during the 19th    and 20th centuries. Geophys. Res. Lett., 27, 2137-2140. Elsner, J. B., 2006: Evidence in support of the climatic cange — Atlantic hurricane hypothesis.    Geophys. Res. Lett., 33, doi:10.1029/2006GL026869. Enfield, D. B., A. M. Mestas-Nuñez, and P. J. Trimble, 2001: The Atlantic multidecadal oscillation and    its relation to rainfall and river flows in the continental U.S. Geophys. Res. Lett., 28, 2077-2080. Enfield, D. B. and L. Cid-Serrano, 2006: Projecting the risk of future climate shifts. Int. J. Climatol., 26,    885-895. Enfield, D. B. and L. Cid-Serrano, 2007: Secular and multidecadal warmings in the North Atlantic and    their relationships with major hurricane activity, J. Climate, submitted. Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nuñez, and W. M. Gray, 2001: The recent increase in    Atlantic hurricane activity: Causes and implications. Science, 474-479. Gray, S. T., J. L. Graumlich, J. L. Betancourt, and G. T. Pederson, 2004: A tree-ring based    reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D. Geophys. Res. Lett., 31,    L12205, doi:10.1029/2004GL019932. Knight, J. R., R. J. Allan, C. K. Folland, M. Vellinga, and M. E. Mann, 2005: A signature of persistent    natural thermohaline circulation cycles in observed climate. Geophys. Res. Lett., 32,    doi:10.1029/2005GL024233. Mann, M. E. and K. Emanuel, 2006: Atlantic hurricane trends linked to climate change. Eos, Trans. of    AGU, 87, 233-244. Sato, M., J. E. Hansen, M. P. McCormick, and J. B. Pollack, 1993: Stratospheric aerosol optical depths,    1850-1990. J. Geophys. Res., 98, 22,987-22,994. Trenberth, K. E. and D. J. Shea, 2006: Atlantic hurricanes and natural variability in 2005. Geophys.    Res. Lett., 33, doi:10.1029/2006GL026894. Wang, C., S.-K. Lee, and D. B. Enfield, 2007: Impact of the Atlantic warm pool on the summer climate    of the Western Hemisphere. J. Climate, submitted. NOAA Atlantic Oceanographic & Meteorological Laboratory

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