Hurricane Upsurge Not Linked to Global Warming, NOAA Concludes

Published February 1, 2006

The U.S. National Oceanic and Atmospheric Administration (NOAA) has concluded the upsurge in recent hurricane activity is not related to global warming.

In a study released November 29, 2005 NOAA concludes the Atlantic Ocean is experiencing more hurricanes because it is in a peak period of a 20- to 30-year natural hurricane pattern.

Natural Cycle Is Peaking

According to NOAA, the U.S. has been in a cycle of heightened Atlantic Ocean hurricane activity for the past 11 years. The cycle began in 1995 and is expected to continue for at least another decade. Importantly, the cycle is part of a naturally occurring pattern and is not in any way related to global warming activity, concluded NOAA.

“NOAA attributes this increased activity to natural occurring cycles in tropical climate patterns near the equator,” states the NOAA study. “These cycles, called ‘the tropical multi-decadal signal,’ typically last several decades (20 to 30 years or even longer). As a result, the North Atlantic experiences alternating decades long (20 to 30 year periods or even longer) of above normal or below normal hurricane seasons. NOAA research shows that the tropical multi-decadal signal is causing the increased Atlantic hurricane activity since 1995, and is not related to greenhouse warming.”

The current upsurge in hurricane activity is similar to the previous cycle of heightened hurricane activity lasting from the late 1920s to the late 1960s. An intervening cycle of below-normal hurricane activity occurred from 1970 to 1994, the NOAA study concludes.

“Since 1995, the tropical multi-decadal signal has produced lower wind shear (changing winds with height) and warmer waters across the tropical Atlantic, along with conducive winds coming off the west coast of Africa. This key combination of conditions produces active hurricane seasons,” explains NOAA. “With an active hurricane era comes many more landfalling tropical storms, hurricanes and major hurricanes in the United States. … The United States can expect ongoing high levels of landfalling tropical storms and hurricanes while we remain in this active era.”

CO2 Not to Blame

Regarding the warmer Atlantic waters, the lower wind shear, and the conducive winds coming off the west coast of Africa, NOAA observes, “Research by NOAA scientists Gerry Bell and Muthuvel Chelliah, currently in press with the Journal of Climate, describes the tropical multi-decadal signal and shows that it accounts for the entire inter-related set of conditions that controls hurricane activity for decades at a time.”

The NOAA study affirms the findings of most hurricane researchers. “There is consensus among NOAA hurricane researchers and forecasters that recent increases in hurricane activity are primarily the result of natural fluctuations,” reports NOAA.

In interviews for this article, three of the nation’s leading hurricane experts agreed with the NOAA assessment.

Chris Landsea, science and operations officer at the NOAA National Hurricane Center in Miami, Florida, observed any impact global warming might have on hurricane activity is neither large nor immediate.

“We may be looking at stronger hurricanes by 5 percent,” Landsea said. “And even that is a very small change that is still way off in the future.”

Even the potential 5 percent change in hurricane strength may be too small to measure. According to Landsea, hurricane experts can estimate a storm’s winds “only to the nearest 5 mph.”

“We can’t even measure that [5 percent change], it’s so small,” Landsea said.

Current Activity Is Normal

Jeff Masters, director of meteorology for the popular Web site Weather Underground, confirmed global warming cannot be blamed for even the warmer Atlantic Ocean temperatures, let alone the other factors necessary for heightened hurricane conditions.

“Everyone agrees the tropical oceans have warmed a half-degree Fahrenheit over the last 100 years,” Masters said. However, he noted, multiple studies on the subject have reached conflicting conclusions on causation.

It is “way too early to say one way or the other” if global warming is responsible, Masters said.

William Gray, head of Colorado State University’s Tropical Meteorology Project, reported that despite media claims to the contrary, most hurricane researchers are skeptical of asserted connections between global warming and recent hurricane activity.

“There is no evidence of changes in tropical storms compared to what we would normally expect during this current cycle,” Gray said.

Kerry Jackson ([email protected]) is a freelance writer.

For more information …

The National Oceanic and Atmospheric Administration’s November 2005 report, “NOAA Attributes Recent Increase in Hurricane Activity to Naturally Occurring Multi-Decadal Climate Variability,” is available online at