Shipwreck rates reveal Caribbean tropical cyclone response to past radiative forcing
Proceedings of the National Academy of Sciences of the United States of America
Assessing the impact of future climate change on North Atlantic tropical cyclone (TC) activity is of crucial societal importance, but the limited quantity and quality of observational records interferes with the skill of future TC projections. In particular, North Atlantic TC response to radiative forcing is poorly understood and creates the dominant source of uncertainty for twenty-first-century projections. Here, we study TC variability in the Caribbean during the Maunder Minimum (MM;
... 5 CE), a period defined by the most severe reduction in solar irradiance in documented history (1610-present). For this purpose, we combine a documentary time series of Spanish shipwrecks in the Caribbean (1495-1825 CE) with a tree-growth suppression chronology from the Florida Keys (1707-2009 CE). We find a 75% reduction in decadal-scale Caribbean TC activity during the MM, which suggests modulation of the influence of reduced solar irradiance by the cumulative effect of cool North Atlantic sea surface temperatures, El Niño-like conditions, and a negative phase of the North Atlantic Oscillation. Our results emphasize the need to enhance our understanding of the response of these oceanic and atmospheric circulation patterns to radiative forcing and climate change to improve the skill of future TC projections. Caribbean | tropical cyclone | Maunder Minimum | dendrochronology | documentary data L andfalling tropical cyclones (TCs) bring devastation to natural and human landscapes with floods, winds, and storm surges. In recent decades, TC-related human mortality and economic losses have risen in step with increasing populations in high-risk coastal communities (1). TC damage is expected to further increase in the near future with rising exposure and projected anthropogenic climate change (2). This is particularly the case for the North Atlantic Basin, which is one of the most TC-active basins globally. The development of successful adaptation and mitigation strategies relies on skillful projections of North Atlantic TC activity, as well as an improved understanding of the drivers of its variability. Modeling studies of twenty-first-century global TC activity generally converge in their projections of increased TC intensity and decreased frequency, but the magnitude range of projected North Atlantic TC variability is wide (3). Uncertainties in twentyfirst-century North Atlantic TC projections are largely driven by the chaotic nature of the climate system and by our limited understanding of TC response to radiative forcing, including anthropogenic greenhouse gases and aerosols, as well as natural variability in volcanic and solar activity (4). Response uncertainty is the dominant source of uncertainty toward the end of the twenty-first century (4), with different model runs resulting in TC responses of opposing sign to projected radiative forcing (3). Our understanding of TC response to radiative forcing-and thus the skill of future TC projections-is restricted by limitations in the time-series length and quality of observational records (5) that hinder trend detection and attribution (3). To attribute significant TC changes to specific climate forcings, recent TC activity needs to be placed in a longer-term context (6). The Maunder Minimum (MM; 1645-1715 CE), the most severe change in solar irradiance in documented history (7, 8) , is of particular interest in this context, but TC proxy records that cover this period are scarce, often present a conservative estimate of the total number of storm events (9), and largely have insufficient time resolution to distinguish the MM (6, 10-12). Documentary data sets are the main source of paleotempestology information of appropriate temporal resolution, but most document-based TC studies have primarily focused on long-term TC climatology (e.g., seasonality, recurrence intervals) rather than interannual or decadal-scale variability (13, 14) . Here, we combine two annual resolution proxy records-a documentary time series of Spanish shipwrecks in the Caribbean (TC ship ) and a tree-growth suppression chronology from the Florida Keys (TC supp )-to extend the observational Caribbean TC (CTC) record back over the last 500 y and thus to cover the MM. Over the past centuries, TCs have caused destruction of human settlements and wreaked havoc at sea. In the Caribbean, TCs were the primary documented cause of shipwrecks in the sixteenth through eighteenth centuries (15) and they left their mark on regional history. For instance, Spanish hegemony over Cuba was secured in 1640 after a hurricane decimated a Dutch fleet poised to attack Havana (15), leading to an additional century of Spanish monopoly over trade between the Caribbean and Europe. We make use of the well-documented maritime TC legacy in the Caribbean region to reconstruct CTC variability. Our reconstruction (TC ship ) is based on a comprehensive documentary compilation (16) of 657 ships of Spanish origin that wrecked in the Caribbean Basin ( Fig. 1A and Tables S1 and S2) over the period 1495-1825 CE due to storms or unspecified factors. Significance Twenty-first-century North Atlantic tropical cyclone (TC) projections are crucial for the development of adaptation and mitigation strategies, but they are subject to large uncertainties, particularly with respect to TC response to radiative forcing. We used a combination of tree-ring data and historical shipwreck data to show that TC activity in the Caribbean was distinctly suppressed during the Maunder Minimum (1645-1715 CE), a period when solar irradiance was severely reduced. This solar fingerprint on decadal-scale Caribbean TC variability implies modulation by a combination of basin-wide climatic phenomena. Our findings highlight the need to enhance our understanding of the response of atmospheric circulation patterns to radiative forcing and climate change to improve the skill of future TC projections.