ORLANDO, Fla. (WTXL) -- The past 15 to 20 years of hurricane seasons have generally features higher numbers of developed tropical systems and memorable, intense major hurricanes reaching land and causing mass devastation.
Some sources cite the impacts of a general warming of the earth's water and surface temperatures over the years, often referred to as "global warming," as a driving force behind the increase in the quantity and strength of tropical cyclones.
But is the connection a solid one?
Chris Landsea, a research meteorologist with an extensive background in hurricane analysis, stated at the annual National Hurricane Conference in Orlando in April that the impacts of possible warmer earth temperatures may not rev up the tropical storm engine.
Landsea pointed to the existence of a cycle of tropical activity, called the multi-decadal oscillation, which shows periods of time with higher tropical activity stretching about 25 to 40 years, blended with similar lengths of time of less tropical activity. The decades of the 1940s through the '60s featured active hurricane seasons, while the 1970s through the early '90s had a general decrease in the number of tropical storms and hurricanes.
With few exceptions, hurricane seasons since 1995 have encountered a drastic uptick in activity, including the record-breaking season of 2005 in which 28 tropical storms formed, exhausting the established list of names and forcing the backup method of using the Greek alphabet to identify the excessive number of late-season storms. Landsea believes the current cycle of more-than-average activity may persist for several more years to come, but not necessarily because of a warmer environment.
Landsea suggests that, even if gradual warming continues, future hurricane seasons won't maintain a level of hyperactivity. Warmer sea surface temperatures may alter upper-level wind patterns that could cause faster winds aloft, which generally hinder a tropical storm's or hurricane's strengthening efforts. The upper atmosphere would also likely warm, causing slightly less of a contrast between lower and upper atmosphere temperatures.
After conducting a series of theory testing through sophisticated computer modeling methods, it was shown that, even with a strong amount of long-term warming, hurricane strength would only increase about 1% by the year 2100. When applied to the peak wind force of Hurricane Katrina, winds would only go from 170 mph to about 172 mph.
However, with the higher amount of wind shear in the upper levels, the number of tropical storms and hurricanes would actually fall. Also, areas of atmospheric drying and sinking air motion could also limit the number of developing storms. In addition, the current water temperature threshold of 80° to sustain a forming tropical cyclone may increase a bit, meaning it would take a warmer sea surface temperature to keep a storm growing.
Additional background into Chris Landsea's findings and research can be found through the website of the Hurricane Research Division of the Atlantic Oceanographic and Meteorological Laboratory.
