Scientists Find No Trend in 370 Years of Tropical Cyclone Data

With Senators Barbara Boxer (D-Calif.) and Frank Lautenberg (D-N.J.) citing Hurricane Sandy as a reason to have another go at climate legislation, to say nothing of the media spin depicting Sandy as punishment for our fuelish ways, it’s useful to look at some actual science.

In a study published in the journal Climatic Change, scientists Michael Chenoweth and Dmitry Divine analyze the history of tropical cyclone activity in the Lesser Antilles from 1638 to 2009. The Lesser Antilles are the string of islands lying along the eastern Caribbean Sea.

The Lesser Antilles intersect the “main development region” for Atlantic hurricane formation, making storm data there “our best source for historical variability of tropical cyclones in the tropical Atlantic in the past three centuries,” the researchers explain.

Using instrumental data on wind speeds (going back to 1900) plus wind-force and wind-induced damage reports for earlier periods, Chenoweth and Divine estimate the Lesser Antilles Accumulated Cyclone Energy (LACE) for each year along the 61.5°W meridian from 18 to 25° N latitude.

Storms forming in this area include most that do or could make landfall in the U.S. In the researchers’ words: “About 60% of all tropical cyclones moving from waters off of Africa pass through 61.5°W south of 25.0°N, the remaining 40% either moving north of 25.0°N, dying out or re-curving to the east of 61.5°W.” Chenoweth and Divine note that LACE is “highly correlated” with Carribbean basin-wide Accumulated Cyclone Energy (ACE) since 1899.

So what did they find? In their words: “Our record of tropical cyclone activity reveals no trends in LACE in the best-sampled regions for the past 320 years. Likewise, even in the incompletely sampled region north of the Lesser Antilles there is no trend in either numbers or LACE.”

Chenoweth and Divine do find a “~50–70 year variability in ACE across the 18–25°N transect.” This wave-like pattern ”is possibly associated with the low-frequency variations in the Atlantic Multi-Decadal Oscillation (AMO), a mode of SST [sea surface temperature] variability that is global in extent but strongest in the Atlantic.” The scientists consider their data “sufficiently complete to be a reliable record back to 1785 and extends the evidence of this pattern further back in time.”

An obvious implication of the study, although not spelled out by the authors, is that natural variability dominates tropical storm activity in the Atlantic to the point that any global warming influence, if it exists, is still undetectable.

For a more detailed review of the study, visit the Center for the Study of Carbon Dioxide and Global Change. Also informative is World Climate Report’s review of Chenoweth and Divine’s 2008 study on tropical cyclones in the Lesser Antilles.