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Climate Change: Impacts on the Caribbean

Climate Change: Impacts on the Caribbean. Dr. Greg Holland. Anthropogenic Influences on Tropical Cyclone Activity in the North Atlantic. Greg Holland National Center for Atmospheric Research. Summary: Trend and Variability Issues on Data Reliability Attribution of Changes The Future.

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Climate Change: Impacts on the Caribbean

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  1. Climate Change: Impacts on the Caribbean Dr. Greg Holland Holland Jamaica 0607…Slide 1

  2. Anthropogenic Influences on Tropical Cyclone Activity in the North Atlantic Greg Holland National Center for Atmospheric Research Summary: Trend and Variability Issues on Data Reliability Attribution of Changes The Future Basic References: Holland and Webster (2007a, PRS; 2007b in preparation) Holland Jamaica 0607…Slide 2

  3. TC1 TC 2 TC3 The Trend 9-year running mean Based on the archived data an accelerating upward trend is one logical choice, though a series of steps is a more logical choice (both TCs and SSTs) Holland Jamaica 0607…Slide 3

  4. 150% Increase 5-y running mean The SST/Tropical Cyclone Relationship We emphasize that the SST-TC relationship is not entirely direct, but also arises from related atmospheric environmental changes (e.g. Goldenberg et al 2001; Delworth 2006; Kossin and Vimont 2007; Holland and Webster 2007b). 2005 1906 Holland Jamaica 0607…Slide 4

  5. The SST/TC, Hurr, Maj Hurr Relationship 10 TCs 4 Hurricanes 2 Maj Hurr Holland Jamaica 0607…Slide 5

  6. Mean Peak Intensity Holland Jamaica 0607…Slide 6

  7. Data Issues Summary of Past Hurricane Proportions • Stable proportions of hurricanes to all tropical cyclones over the past 50-100 years (the higher earlier proportions are considered due to analysis errors); • Stable major hurricane proportions but with a marked, multi-decadal oscillation (peaks associated with equatorial developments and expansion of the warm pool). Holland Jamaica 0607…Slide 7

  8. Summary of Past Hurricane Numbers Holland Jamaica 0607…Slide 8

  9. Are the Observed Increases Real? Holland Jamaica 0607…Slide 9

  10. Missing Early Data? • Neumann (2005) ~1 storm per year based on shipping routes • Landsea (2006) 0-4 storms per year early 1900s and up to 6 before 1900 based on HURDAT reanalysis • Landsea (2007) 2-3 prior to 1970 based on landfalling ratios • Holland and Webster (2007) ~ 1-2 storm per year before 1950 based on proximity to land and shipping routes, increase in subtropical systems 1970 due to changing NHC practice • Vecchi et al (2007) ~ 2 storms per year in early 1900s, dropping to zero by 1960 based on simulated ship movements, still leaves significant trend since 1906 • Kossin et al (2007) confirmed the intensity trend since 1983 • Nyberg et al (2007) ~3 major hurricanes in late 1900s based on coral cores Holland Jamaica 0607…Slide 10

  11. Landfalling Tropical Cyclones • Landfall on US does not show a marked trend, though recent experience is at an all-time high; Curry (2007) Holland Jamaica 0607…Slide 11

  12. nwest neast GOM seast swest Considering All the Data Holland Jamaica 0607…Slide 12

  13. Eastern vs Western Genesis Changing landfall numbers is due more to decreasing western region genesis than to an eastward expansion!! Note that the step changes in numbers are due equally to western and eastern region genesis! Holland Jamaica 0607…Slide 13

  14. Regional Genesis Breakdown Holland Jamaica 0607…Slide 14

  15. 1956-2005 Genesis 1906-1955 Genesis + + - + Why the Landfall Inconsistency? • Genesis increases have been mainly in eastern tropical regions (the infamous Cape Verde Storms); • Western Caribbean and southern Gulf of Mexico have decreased; • Leads to lowered probability of Jamaican Impacts. Holland Jamaica 0607…Slide 15

  16. Hurricanes Major Hurricanes Occurrence Frequency: Jamaica, Bahamas and Barbados Florida Jamaica Barbados Holland Jamaica 0607…Slide 16

  17. Error Bars Vecchi et al (2007) find 2-3 missing storms before 1900 decreasing to zero at 1960; This agrees with a simple test of assuming constant hurricane proportionality at post 1970 values; Holland Jamaica 0607…Slide 17

  18. 9-year running mean The Trend with Errors After adjusting for probable maximum errors, a trend remains; Knutson (pers comm) has shown that this is significantly different from chance at 95% from 1900, but not from 1885; Note that the bulk of the trend is in the satellite era. Holland Jamaica 0607…Slide 18

  19. Attribution of Changes Holland Jamaica 0607…Slide 19

  20. Attribution by Peak Bodies • WMO IWTC-VI: • Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point. • IPCC: • Likely that increases have occurred in some regions since 1970; • More likely than not a human contribution to the observed trend; • Likely that there will be future increasing trends in tropical cyclone intensity and heavy precipitation associated with ongoing increases of tropical SSTs. 9-year running mean SST has same characteristic variability as cyclone numbers and explains >60% of the variability Holland Jamaica 0607…Slide 20

  21. Natural Variability vs Climate Trend? We address the causal relationship: SST signal Relationship between SST and Hurricanes Natural variability or Climate Trend (After Curry Webster and Holland 2006) Holland Jamaica 0607…Slide 21

  22. SST-Hurricane Relationship • Webster et al (2005), Emanuel (2005) and Hoyas et al (2006) noted a strong global relationship with climatological intensity changes. • Gray (1990), Landsea et al (1999), Goldenberg et al (2001), Vitart and Anderson (2001) all find a strong relationship between eastern North Atlantic SSTs and tropical cyclones. • We have shown that Eastern North Atlantic SSTs explain >60% of smoothed variance in Atlantic Tropical Cyclones since 1905 (due entirely to regime changes); • We again emphasize that the SST-TC relationship is not entirely direct, but arises also from related atmospheric environmental changes. Holland Jamaica 0607…Slide 22

  23. Global Surface Temperature Variability Volcano Greenhouse Gases Solar “Natural” Forcing Sulfate There is no known natural forcing mechanism that can explain the surface temperature increases since 1960 (Meehl et al 2004, 2006). IPCC concluded that it was virtually certain that the SST increases are substantially due to anthropogenic causes. Ozone Holland Jamaica 0607…Slide 23

  24. Atlantic SST Variations and Trends Atlantic Multidecadal Oscillation or North Atlantic Oscillation? Various claims of a relationship (Bell and Chelliah 2005, Goldenberg et al 2001) BUT Mann and Emanuel (2006), Trenberth and Shea (2005), Bryden et al (2005), Santer et al. (2006) and others disagree. Conclude a small contribution by NAO, but major contribution has been anthropogenic. Peak Trough EA= Eastern North Atlantic; WA=Western North Atlantic; GM=Gulf of Mexico; and EPAC=Eastern North Pacific. All filtered by 9-year running mean. Holland Jamaica 0607…Slide 24

  25. Interim Conclusion • The increasing frequency of tropical cyclones over the past century cannot be explained by data errors alone; • The logical conclusion is that there has been a substantial anthropogenic contribution arising from the warming of the oceans; • This is consistent with the climate change modeling studies by Oochi et al (2006), Bengtsson et al 2007, and recent unpublished modeling work by Knutson et al.; • There has been no increase in either intensity or the proportion of major hurricanes, which is consistent with Henderson-Sellers et al (1998); • However, while the proportion of major hurricanes has no trend, the number has increased substantially. But what of the physical connections? Holland Jamaica 0607…Slide 25

  26. Why the Eastward Expansion? • Increases are consistent with the expansion of the North Atlantic Warm Pool. Hoyos and Webster (2007) Holland Jamaica 0607…Slide 26

  27. Global Cyclogenesis Regions Holland Jamaica 0607…Slide 27

  28. When Waves Accumulate Holland Jamaica 0607…Slide 28

  29. Compare 2005 with 1991-1993 • 2005: • Record 30% of AEWs spawned tropical cyclones and 10% became hurricanes (Avila pers. Corresp); • AEW developments provided 10 of the 14 hurricanes in 2005, all category 3-5 hurricanes, all tropical cyclones in July and August, and 8 of the 11 tropical cyclones in September and October; • Two AEWs also generated two tropical cyclones each, a rare event that last occurred in 1988; • 1991-1993: • Representative of a 20-year period of weakened equatorial cyclogenesis; • No tropical cyclones formed in July, only 1 in October, and only one hurricane developed from AEWs. Holland Jamaica 0607…Slide 29

  30. OLR a SST b U 200 hPa c U 850 hPa d Difference Fields 2005 to 1991-1993 Holland Jamaica 0607…Slide 30

  31. Cyclogenesis Relative to OLR/SST Max Most tropical cyclones and all but one of the major hurricanes formed west of the maximum OLR/SST anomaly, in decreased vertical wind shear and more negative dU/dx Holland Jamaica 0607…Slide 31

  32. Compare July Conditions 2005 1991-1993 Holland Jamaica 0607…Slide 32

  33. Equatorial Rossby Wave Note the merdional stretching, consistent with observations that two TCs formed from one wave on two occasions, the first time since 1988 Holland Jamaica 0607…Slide 33

  34. 2005 Equatorial Tropical Cyclones All formed in regions of wave accumulation (-dU/dx). See also Holland (1995), Maloney and Hartmann (2000, 2001) Holland Jamaica 0607…Slide 34

  35. Return to Changes in the Warm Pool Hoyos and Webster (2007) Holland Jamaica 0607…Slide 35

  36. Some Speculation Increasing eastern equatorial development… Results in cooler western oceans due to cyclone upwelling, locks in a climatic regime… Explains the lower activity in the Caribbean compares to the total basin… Results in a higher proportion of major hurricanes. Holland Jamaica 0607…Slide 36

  37. NCAR Prediction Across Scales • Finished: • Tropical Channel at 36 km for 1996-2005 • 2-way nests to 4 km resolution for up to 1 year • 12 km for entire North Atlantic Hurricane region for 2005 season…4km run planned • Future plan to include climate change period • Moving towards a new climate/weather model capable of <1km resolution predictions, with emphasis on decadal time scales • We encourage collaborations in this effort. Click: start simulation Holland Jamaica 0607…Slide 37

  38. “The future comes apace” William Shakespeare ? • 5-10Year Outlook • 1-2-Year Variability • 20-30-Year Outlook Holland Jamaica 0607…Slide 38

  39. 5-10 year Activity Outlook • Virtually certain that the current high level of activity will remain at the same or higher levels; • Note that: • The current upward surge in cyclone numbers has not yet stabilized, running at 14 per year on average since 1995; • NAO contribution will result in an increase until 2020 or thereabouts; • Simple historical extrapolation indicates that the proportion of major hurricanes will continue higher and take 10-20 years to return to lower levels; • But everything depends on El Nino Holland Jamaica 0607…Slide 39

  40. 30-50 Year Outlook • Must rely on climate models; • Considerable uncertainty and potential errors, esp El Nino; • Oochi et al 2006: • Increase in numbers in North Atlantic, decrease elsewhere; • Small increase in intensity globally; • Bengtsson et al 2007: • Stable or slightly increased numbers in North Atlantic and eastern North Pacific, decrease elsewhere; • General small increase in intensity, but 30% increase in major hurricanes in North Atlantic by 21st century. Holland Jamaica 0607…Slide 40

  41. Hurricanes Major Hurricanes Jamaica, Florida and Barbados Difficult to assess: Speculate a lower response than for the basin at large, but more major hurricane impacts; Sea-level rise and rainfall are major amplifying factors. Holland Jamaica 0607…Slide 41

  42. Other Factors • It is too late for preventive emission actions to have an effect for decades yet. Adaptation is required; • Sea Level Rise will substantially amplify impacts; • Rainfall will increases substantially ~ 7% per 1oC ocean warming (e.g. Trenberth and Fasullo 2007), which will increase the danger of flooding and related landslide problems; • Overland Damage from Tornadoes and Local Wind Bursts is unknown; • Demographic and Commercial Activity Changes: • Statement of concerned scientists; • In some quarters sold as implying no real importance of changes in hurricane characteristics (Pielke et al), whereas it really means the meteorological and oceanic changes become more important (e.g. Anthes etal 2007). Holland Jamaica 0607…Slide 42

  43. Summary • Substantial trend in North Atlantic tropical cyclones and hurricanes and both a multidecadal oscillation and trend in major hurricanes: • Cannot be explained entirely by data errors; • Strongly related to Atlantic SST and thus to both long-period oscillations, such as the North Atlantic Oscillation (NAO) and Greenhouse Warming; • GW is the dominant factor; • Physical reasoning indicates the changes are more related to associated circulation changes than direct SST response: • AEW accumulation; • Reduced and more easterly vertical shear; • Trap wave energy in lower atmosphere. • It is most likely that current elevated activity in the North Atlantic will continue for at least the next 5-10 years and will include a high proportion of major hurricanes. • The decadal trends are grim, with up to a 30% increase in major North Atlantic hurricanes being projected. Holland Jamaica 0607…Slide 43

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