Paleotempestology is a field of science with important practical and social implications.[20] The insurance industry factors in paleotempestological information in risk prediction analysis[90] and when setting insurance rates,[69] and it also funds paleotempestological research.[91] Archeologists, ecologists, forest and water resource managers could also make use of paleotempestology information.[11]
Recurrence rates
The recurrence rate is an important metric with which one can estimate tropical cyclone risk, and it can be determined by paleotempestological research. In the Gulf of Mexico, catastrophic hurricane strikes at given locations occur once about every 350 years in the last 3,800 years[22] or about 0.48%-0.39% annual frequency at any given site,[92] with a recurrence rate of 300 years or 0.33% annual probability at sites in the Caribbean and Gulf of Mexico;[93] category 3 or more storms occur at a rate of 3.9 - 0.1 category 3 or more storms per century in the northern Gulf of Mexico.[94] Elsewhere, tropical cyclones with intensities of category 4 or more occur about every 350 years in the Pearl River Delta (China),[95] 1 storm every 100–150 years at Funafuti and a similar rate in French Polynesia,[80] 1 category 3 or stronger every 471 years in St. Catherines Island (Georgia),[96] 1 storm every 140–180 years in Nicaragua,[97] 1 intense storm every 200–300 years in the Great Barrier Reef[48] - formerly their recurrence rate was estimated to be one strong event every few millennia[98] - and 1 storm of category 2-4 intensity[99] every 190–270 years at Shark Bay on the other side of Australia.[100]Steady rates have been found for the Gulf of Mexico and the Coral Sea[101] for timespans of several millennia.[92]
However, it has also been found that the occurrence rates of tropical cyclone measured with instrumental data over historical time can be significantly different from the actual occurrent rate. In the past, tropical cyclones were far more frequent in the Great Barrier Reef[48] and the northern Gulf of Mexico than today;[102] in Apalachee Bay, strong storms occur every 40 years, not every 400 years as documented historically.[103] and serious storms in New Yorkoccurred twice in 300 years[104] not once every millennium or less.[105] In general, the area of Australia appears to be unusually inactive in recent times by the standards of the past 550–1500 years,[106] and that the historical record underestimates the incidence of strong storms in Northeastern Australia.[107]
Long term fluctuations of tropical cyclone activity
Long-term variations of tropical cyclone activity have also been found. The Gulf of Mexico saw increased activity between 3,800 - 1,000 years ago with a fivefold increase of category 4-5 hurricane activity,[108] and activity at St. Catherines Island and Wassaw Island was also higher between 2,000 and 1,100 years ago.[109] This appears to be a stage of increased tropical cyclone activity spanning the region from New York to Puerto Rico,[110] followed by an inactive interval since 1,000 years that also affected the Gulf Coast.[111] The US Atlantic coast and the Caribbean saw low activity between 950 ADand 1700 with a sudden increase around 1700.[40]Such fluctuations appear to mainly concern strong tropical cyclone systems, at least in the Atlantic; weaker systems have a more steady pattern of activity.[112] Rapid fluctuations over short timespans have also been observed.[11]
In the Atlantic Ocean, the so-called "Bermuda High" hypothesis stipulates that changes in the position of this anticyclone can cause storm paths to alternate between landfalls on the East Coast and the Gulf Coast[19][113] but also Nicaragua.[114]Paleotempestological data support this theory[115]although additional findings on Long Island and Puerto Rico have demonstrated some complexity in the patterns[111] as active periods appear to correlate between the three sites.[116] A southward shift of the High has been inferred to have occurred 3,000[117]-1,000 years ago[118] and has been linked with the "hurricane hyperactivity" period in the Gulf of Mexico between 3,400 - 1,000 years ago.[119]Furthermore, a tendency to a more northerly storm track may be associated with a strong North Atlantic Oscillation[120] while the Neoglacial cooling is associated with a southward shift.[119] A north-south anti-correlation has also been found in West Asia between the South China Sea and Japan.[121]
Influence of climate modes on tropical cyclone activity
The influence of natural trends on tropical cyclone activity has been recognized in paleotempestology records, such as correlation of Atlantic hurricanetracks[122] and activity with the status of the ITCZ,[123][124] position of the Loop Current (for Gulf of Mexico hurricanes),[92] North Atlantic Oscillation, sea surface temperatures[125] and the strength of the West African Monsoon,[126] and correlation between Australian cyclone activity and the Pacific Decadal Oscillation.[127] Increased insolation - either from solar activity[128] or from orbital variations - have been found to be detrimental to tropical cyclone activity in some regions.[129] In the early Common Era, warmer sea surface temperatures in the Atlantic as well as more restricted anomalies may be responsible for stronger regional hurricane activity.[130]
Among the known climate modes that influence tropical cyclone activity in paleotempestological records are ENSO phase variations, which influence tropical cyclone activity in Australia and the Atlantic[131] but also their path as has been noted for typhoons.[132][133] More general global correlations have been found, such as anticorrelation between tropical cyclone activity in Japan and the North Atlantic[129] and correlation between the Atlantic and Australia on the one hand[134] and between Australia and French Polynesia on the other hand.[135]
Influence of long-term temperature variations on tropical cyclone activity
The effect of general climate variations have also been found. Hurricane[136] and typhoon tracks tend to shift north (e.g. Amur Bay) during warm periods and south (e.g. South China) during cold periods,[137]patterns that might be mediated by shifts in the subtropical anticyclones.[111] Such a behaviour (northward shift) has been observed as a consequence of man-made global warming and the end of the Little Ice Age[136] but also after volcanic eruptions (southward shift).[138]
During the last 600 years in the Little Ice Age, there were more but weaker storms in the Gulf of Mexico[139] while hurricane activity did not decrease in western Long Island.[116] Increased hurricane activity during the last 300 years in the Caribbean may also correlate to the Little Ice Age.[140]
The response of tropical cyclone to future global warming is of great interest. The Holocene Climatic Optimum did not induce increased tropical cyclone strikes in Queensland and phases of higher hurricane activity on the Gulf Coast are not associated with global warming;[40] however warming has been correlated with typhoon activity in the Gulf of Thailand[141] and marine warming with typhoon activity in the South China Sea,[142] increased hurricane activity in Belize (which increased during the Medieval Warm Period)[143] and during the Mesozoic, when carbon dioxide caused warming episodes.[89]
https://en.m.wikipedia.org/wiki/Paleotempestology