Shipwreck rates reveal Caribbean tropical cyclone response to past radiative forcing Valerie Troueta,1, Grant L. Harleyb, and Marta Domínguez-Delmásc,d aLaboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721; bDepartment of Geography and Geology, University of Southern Mississippi, Hattiesburg, MS 39402; cDepartment of Botany, University of Santiago de Compostela, 27002 Lugo, Spain; and dDepartment of History I, University of Huelva, 21071 Huelva, Spain Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved February 2, 2016 (received for review October 2, 2015) Assessing the impact of future climate change on North Atlantic most severe change in solar irradiance in documented history (7, tropical cyclone (TC) activity is of crucial societal importance, but the 8), is of particular interest in this context, but TC proxy records limited quantity and quality of observational records interferes with that cover this period are scarce, often present a conservative the skill of future TC projections. In particular, North Atlantic TC estimate of the total number of storm events (9), and largely have response to radiative forcing is poorly understood and creates the insufficient time resolution to distinguish the MM (6, 10–12). dominant source of uncertainty for twenty-first-century projections. Documentary data sets are the main source of paleotempestology Here, we study TC variability in the Caribbean during the Maunder information of appropriate temporal resolution, but most docu- Minimum (MM; 1645–1715 CE), a period defined by the most severe ment-based TC studies have primarily focused on long-term TC reduction in solar irradiance in documented history (1610–present). climatology (e.g., seasonality, recurrence intervals) rather than For this purpose, we combine a documentary time series of Spanish interannual or decadal-scale variability (13, 14). Here, we combine shipwrecks in the Caribbean (1495–1825 CE) with a tree-growth two annual resolution proxy records—a documentary time series suppression chronology from the Florida Keys (1707–2009 CE). We of Spanish shipwrecks in the Caribbean (TCship)andatree-growth find a 75% reduction in decadal-scale Caribbean TC activity during suppression chronology from the Florida Keys (TCsupp)—to ex- the MM, which suggests modulation of the influence of reduced tend the observational Caribbean TC (CTC) record back over the solar irradiance by the cumulative effect of cool North Atlantic sea last 500 y and thus to cover the MM. – surface temperatures, El Niño like conditions, and a negative phase Over the past centuries, TCs have caused destruction of hu- of the North Atlantic Oscillation. Our results emphasize the need man settlements and wreaked havoc at sea. In the Caribbean, to enhance our understanding of the response of these oceanic TCs were the primary documented cause of shipwrecks in the and atmospheric circulation patterns to radiative forcing and cli- sixteenth through eighteenth centuries (15) and they left their mate change to improve the skill of future TC projections. mark on regional history. For instance, Spanish hegemony over Cuba was secured in 1640 after a hurricane decimated a Dutch Caribbean | tropical cyclone | Maunder Minimum | dendrochronology | fleet poised to attack Havana (15), leading to an additional documentary data century of Spanish monopoly over trade between the Caribbean and Europe. We make use of the well-documented maritime TC EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES andfalling tropical cyclones (TCs) bring devastation to natu- legacy in the Caribbean region to reconstruct CTC variability. Lral and human landscapes with floods, winds, and storm Our reconstruction (TCship) is based on a comprehensive docu- surges. In recent decades, TC-related human mortality and mentary compilation (16) of 657 ships of Spanish origin economic losses have risen in step with increasing populations in that wrecked in the Caribbean Basin (Fig. 1A and Tables S1 high-risk coastal communities (1). TC damage is expected to and S2) over the period 1495–1825 CE due to storms or further increase in the near future with rising exposure and unspecified factors. projected anthropogenic climate change (2). This is particularly the case for the North Atlantic Basin, which is one of the most Significance TC-active basins globally. The development of successful adap- tation and mitigation strategies relies on skillful projections of North Atlantic TC activity, as well as an improved understanding Twenty-first-century North Atlantic tropical cyclone (TC) pro- of the drivers of its variability. jections are crucial for the development of adaptation and Modeling studies of twenty-first-century global TC activity mitigation strategies, but they are subject to large uncer- generally converge in their projections of increased TC intensity tainties, particularly with respect to TC response to radiative forcing. We used a combination of tree-ring data and historical and decreased frequency, but the magnitude range of projected shipwreck data to show that TC activity in the Caribbean was North Atlantic TC variability is wide (3). Uncertainties in twenty- distinctly suppressed during the Maunder Minimum (1645– first-century North Atlantic TC projections are largely driven by 1715 CE), a period when solar irradiance was severely reduced. the chaotic nature of the climate system and by our limited un- This solar fingerprint on decadal-scale Caribbean TC variability derstanding of TC response to radiative forcing, including an- implies modulation by a combination of basin-wide climatic thropogenic greenhouse gases and aerosols, as well as natural phenomena. Our findings highlight the need to enhance our variability in volcanic and solar activity (4). Response uncertainty understanding of the response of atmospheric circulation pat- is the dominant source of uncertainty toward the end of the terns to radiative forcing and climate change to improve the twenty-first century (4), with different model runs resulting in TC skill of future TC projections. responses of opposing sign to projected radiative forcing (3). Our understanding of TC response to radiative forcing—and thus the Author contributions: V.T., G.L.H., and M.D.-D. designed research, performed research, skill of future TC projections—is restricted by limitations in the analyzed data, and wrote the paper. time-series length and quality of observational records (5) that The authors declare no conflict of interest. hinder trend detection and attribution (3). This article is a PNAS Direct Submission. To attribute significant TC changes to specific climate forc- 1To whom correspondence should be addressed. Email: [email protected]. ings, recent TC activity needs to be placed in a longer-term This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. context (6). The Maunder Minimum (MM; 1645–1715 CE), the 1073/pnas.1519566113/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1519566113 PNAS | March 22, 2016 | vol. 113 | no. 12 | 3169–3174 Downloaded by guest on September 26, 2021 TCship does not overlap in time with the North Atlantic TCsupp captures 40 of the 44 storms—occurring during 31 out Hurricane Database (HURDAT; 1851–2010 CE) (17) and there- of a total of 34 storm years—that tracked within 160 km of Big fore we used TCsupp (1707–2009 CE) to assess its validity as a Pine Key over the instrumental period (Figs. 1A,2A, and S1; CTC proxy. TCsupp is based on 38 south Florida slash pine (Pinus Tables S3 and S4). Widespread suppressions in tree growth (high 2 elliottii var. densa) trees from Big Pine Key that show common TCsupp values) corresponded to storm years (χ = 255, P < 0.001) 0 patterns of suppressed growth (Fig. 1B). The primary causes of and typically occurred the same year (t ; P < 0.001) or 1 y after +1 tree-growth suppressions in the Florida Keys are high-energy (t ; P < 0.01) a TC event (Figs. 1C and 2A). We interpret the winds and storm-surge-induced saltwater intrusion and TCsupp double peak in the superposed epoch analysis (SEA) results to thus reflects interannual variability in landfalling CTCs. Owing represent the immediate or delayed effect of wind and storm to the geography and regional positioning of the Florida Keys surge damage on tree growth. The timing of a TC event during relative to the Caribbean Sea and Atlantic Ocean (Fig. 1A) and the hurricane season (August to October) relative to the growing to the decadal-scale relationship between landfalling and basin- season of trees (February to November) (20) likely dictates 0 +1 wide TC dynamics (18, 19), TCsupp canalsobeinterpretedtore- whether suppression in growth occurs at t or t , but a signifi- flect Caribbean basin-wide TC dynamics. cant pattern was not found. A BC0.6 0.4 0.2 simulated) 0 PDSI (departure actual from -0.2 -3 -2 -1 01 23 Lag year Fig. 1. Geographical location, storm-induced tree growth suppression, and its climatic signal at Big Pine Key, Florida. (A) Geographical location of the BPK tree-ring site (red dot), HURDAT-derived (1851–2010 CE) (17) category 1–5 TCs (white lines; n = 44) that tracked within 160 km (red buffer ring) of the site, and countries/states for which shipwrecks were recorded (black shading) (16); (B) Slash pine (P. elliottii var. densa) section (dated over 1707–1829 CE) with tree- growth suppressions (multiple consecutive narrower-than-average annual rings) resulting from TC events indicated by date of recorded TC event; (C)SEA (1895–2009 CE) of TCsupp event series (defined as years when >75% of samples showed growth suppression; n = 12) with July–November Palmer Drought Severity Index (PDSI) for Florida climate division 7. 3170 | www.pnas.org/cgi/doi/10.1073/pnas.1519566113 Trouet et al. Downloaded by guest on September 26, 2021 AB C Fig. 2. Instrumental and reconstructed CTC activity. SEA of the TCsupp time series with instrumental [HURDAT, ref. 17; 1851–2010 CE] (A); and reconstructed (TCship; 1495–1825 CE) (B) CTC events.