NOAA Reports Explains Increase in Hurricane Activity

Amen. Maybe the national media should put that on the news. They won't. Instead, we'll get more of Bill Nie "the Science Guy"(who doesn't know a damn thing about meteorology) going on about how global warming is causing the hurricanes. I'm glad to see NOAA finally came out and said something. Now all we need is NHC to come out and say the same thing.
Meteorologists have known about the inter-decadal cycle and that we had entered a newly active phase of the cycle for a long time. This doesn't mean that it is the sole factor in increased activity, the same problem that applies with disattributing a single event to global warming applies to attributing it at least some partial factor; there's just no way to really discern. Certainly, there have been several highly anomalous things that are NOT normal and that have not been observed before. They could just be flukes, and our modern observation infrastrucutre certainly makes a difference in the quantity and quality of information.

The bottom line is just because a natural cycle predicts an increase, in the scheme of things, not much is really known about the details of that cycle (we've only observed a couple). In the same manner that one should be skeptical of any claims of global warming causation, one shouldn't automatically leap to the conclusion that all answers with increased activity lie in the multi-decadel signal either. Indeed, from the NOAA release (emphasis added):
There is consensus among NOAA hurricane researchers and forecasters that recent increases in hurricane activity are primarily the result of natural fluctuations in the tropical climate system known as the tropical multi-decadal signal.

Recent work finds a 30-year global increase in hurricane intensity strongly correlated with rising SSTs, although not conclusive such a strong signal on a global scale which effectively cancels out local cycles is quite interesting. Other factors are involved of course, but more ocean heat makes for more intense storms all things being equal, and the other factors involved require refining as does actual water temp influence. Also, the occurrence of "Hurricane Catarina", only the second named storm ever observed in the south Atlantic (a TS formed off the African coast in the early 90s before the current active part of the cycle began), the first named storm ever observed in the western south Atlantic, and the first known hurricane ever in the enitre south Atlantic, in 2004 was unheardof; textbook meteorology says storms don't form in the southern Atlantic due to cooler temps and/or shear. but the occurrence of tropical cyclones there is predicted by some climate change models, and this occurred in an area that is expected to be drier in the current stage of the multi-decadel cycle (from NOAA release):

"The first South Atlantic hurricane: Unprecedented blocking, low shear and climate change" by Alexandre Bernardes Pezza and Ian Simmonds, Geophysical Research Letters (Vol 32, L15712, doi:10.1029/2005GL023390, 2005).

All this said, I agree that the current rise is (probably) primarily resultant of the tropical multi-decadal signal, and that the media has been irresponsible in how it has presented the information and floated unsubstantied claims about global warming causing the rise in hurricanes and specifically Katrina.


Increasing destructiveness of tropical cyclones over the past 30 years by Kerry Emanuel, Nature (Vol 436, 4 August 2005, doi:10.1038/nature03906).

Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment by P. J. Webster et al, Science (16 September 2005, Vol 309, 10.1126/science.1116448).

Uncertainty in Hurricanes and Global Warming by Kevin Trenberth, Science (17 June 2005, Vol 308, 10.1126/science.1112551).

Hurricanes and Global Warming by R. A. Pielke Jr., et al (Bulletin of the American Meteorological Society, November 2005).
American Meteorological Society’s
Environmental Science Seminar Series
Hurricanes: Are They Changing and Are We Adequately Prepared for the Future?

Dr. Anthony Socci, Senior Fellow, American Meteorological Society
Dr. Kevin Trenberth, Head of the Climate Analysis Section, National Center for Atmospheric Research (NCAR), Boulder, CO
How are hurricanes changing with global warming
Dr. Judith Curry, Professor and Chair of the School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA
Changes in hurricane intensity in a warming environment
Dr. Kerry Emanuel, Professor of Atmospheric Science, Massachusetts Institute of Technology, Cambridge, MA
Hurricanes and Climate

Are the bonanza Atlantic hurricane seasons of 2004 and 2005 becoming the norm? Is the record breaking number of typhoon hits in Japan in 2004 a wave of the future? Does the first known hurricane, Catarina, in the South Atlantic in March 2004 signal more? The climate is changing, and humans are partly responsible. Global mean temperatures continue to increase and are running 1°F or more above pre-1970s values. While 1998 remains the warmest year on record, 2002, 2003 and 2004 follow closely behind. These changes have been definitively linked to increases in greenhouse gases in the atmosphere, most notably carbon dioxide, which has increased 30% in the past century and half of that increase has occurred since 1970. This increase is from human activities and especially the burning of fossil fuels. As part of this global warming, sea surface temperatures (SSTs) in the tropics have increased 0.9°F since the early 1970s, and this increase is unprecedented over at least the last 150 years and perhaps the last several thousand years. It is almost certainly a result of the additional greenhouse gases mankind has put into the atmosphere. Associated with this is an observed increase in atmospheric moisture (water vapor) on the order of 4%.
Recent scientific research suggests that the duration and intensity of hurricanes worldwide has increased dramatically over the last 30-50 years. Analysis of global hurricane data from satellites (which is available since 1970) shows that the strongest hurricanes (categories 4+5) have almost doubled for the period 1970-2004, and this increase is seen in each of the ocean basins for which hurricanes occur. This increase in hurricane intensity is coincident with a global increase in tropical sea surface temperature, which is evident in each of the ocean basins. In fact, tropical ocean temperature has increased by about 1°F over the past 50 years, and this increase is unprecedented over at least the last 150 years and perhaps the last several thousand years. While sea surface temperature is not the only thing that determines hurricane intensity, there is strong empirical and theoretical evidence that on average an increase in sea surface temperature will increase the average intensity of hurricanes. What has been producing this warming? Solar and volcanic activity have actually been working during this period to produce a slight global cooling. As stated above, the decadal scale variability seen in the North Atlantic is regional and cannot explain the global increase in tropical sea surface temperatures. Particularly during the period since 1970, greenhouse warming is the best explanation that we have for this temperature increase.


Position Paper on Tropical Cyclones and Climate Change (Revised and Updated, Sept., 2005) (An update to Kerry Emanuel's August 2005 paper in Nature)