Are Hurricanes Stronger GLOBALLY?

[Maestro]

I was reading an article about how some people are saying that global warming is causing an increase in the intensity and frequency of hurricanes. It appears to me that they are basing this theory on the stronger Atlantic storms headed to the U.S.

My question is this. If global warming is indeed increasing hurricance strength, then wouldn't hurricanes all over the globe be increasing in intensity and frequency? Is this indeed the case?

Thanks,
M

[x-y-no]

Intensity, yes.

Frequency, no.

Some enlightening discussion of this can be found in this article:

http://www.realclimate.org/index.php?p=181

EDIT:

Actually, more directly to the point may be this article:

http://www.realclimate.org/index.php?p=173

[iceangel]

http://news.nationalgeographic.com/news ... rming.html

[donsutherland1]

In his October 2005 discussion, Dr. Gray has weighed into this issue. Excerpts follow:


This year’s major hurricanes Dennis, Katrina and Rita and last year's four U.S. landfalling major hurricanes have spawned an abundance of questions concerning the role that global warming might be playing in these events. The ideas that global warming may have been partly responsible for the last two years of greater landfalling hurricane activity has been enhanced by two recent papers presenting data to show that global tropical cyclones have become more intense in recent years. They speculate that this increased hurricane activity may be due to human-induced global warming. These papers are:



a) Kerry Emanuel, 4 August 2005: Increasing destructiveness of tropical cyclones over the past 30 years. Nature, 436, 686-688.



b) P.J. Webster, G.J. Holland, J. Currie and P. Chang, 16 September 2005: Changes in tropical cyclone number, duration, and intensity in a warming environment. Science, 309, 1844-1846.



The first author’s comments concerning some of the flaws in the data sets that these papers used will be sent to the respective journals and will be put in the 2005 seasonal verification paper in a summarized form.



These papers’ implications that a Power Dissipation Index (PDI) (related to tropical cyclone intensity) has increased markedly in the Northwest Pacific and Atlantic over the last 30 years (Emanuel) and that global Category 4-5 tropical cyclone activity has gone up over the last 15 years (Webster et al.) from the prior 15 years are likely not valid. Several factors need to be considered when evaluating these papers:



1) The SSTs of the ocean basins where TCs form have warmed very little in the last 30 years (~0.2-0.3oC). This warming is less than the 30 year warming of the whole globe. Ocean temperature change has been matched by upper tropospheric warming. Lapse rates and rainfall in the various tropical cyclone basins have shown no significant change. We have no theory to relate TC basin SST variation to hurricane frequency and intensity when SST variations are so small.



2) The Atlantic has special multi-decadal variations in major hurricane activity that are not present in other basins. These changes are not related to global temperature but to multi-decadal variations of the Atlantic thermohaline circulation, sometimes referred to as the Atlantic multidecadal oscillation (AMO). For example, there was naturally-occurring low major hurricane activity in the Atlantic from 1970-1994 and high major hurricane activity in the Atlantic from 1995-present.



3) There are special difficulties in using the NW Pacific data sets during the years of 1973-1986 when the Atkinson-Holliday (1977) wind pressure scheme was employed. This is now well-accepted to have given typhoon maximum wind speeds that were much too low. Much of the increase in a hurricane’s maximum winds from this period to the present is not real but due to erroneous wind under-estimates during the earlier period.



4) Major (Cat. 3-4-5) hurricane activity in the Northeast Pacific has gone down during the last two 15-year periods from 80 (1975-1989) to 74 (1990-2004), but the Webster et al. paper shows an increase in Category 4-5 tropical cyclones from 36 to 49. This requires that Category 3 tropical cyclones decreased from 44 during 1975-1989 to 25 during 1990-2004. This is highly unlikely. SSTs in the NE Pacific increased by only 0.1oC between these two periods.



5) Satellite technology and user training experience in the Southern Hemisphere in the period of 1975-1989 was not adequate to be able to make the fine distinction between a Category 4-5 hurricane and a Category 3 hurricane or the distinction of a storm with sustained surface winds above or below 130 mph. The Webster et al. paper states that Southern Hemisphere Category 4-5 hurricanes increased from 33 to 72 from 1975-1989 to 1990-2004. This requires that Category 3 hurricane increased from only 42 to 48 during the same period. This is not physically plausible. It is also not physically possible that Southern Hemisphere major (Cat. 3-4-5) hurricanes nearly doubled from 75 to 130 from 1975-1989 to 1990-2004. Physical features present during the last 15 years were not that different from the prior 15 years.

[jasons2k]

Thanks Don.

[x-y-no]

I haven't had opportunity to read the Emmanuel and Webster papers yet, although I've read discussion of them. One thing that jumps out is it was my understanding that Emmanuel used a data set back to circa 1950, and Webster back to 1970.

Also, if there are well understood problems with the NW Pacific data from 73 through 86, I find it hard to believe that Webster et. al. passed peer review without that issue having been raised and dealt with.

But I'll certainly keep Dr. Gray's comments in mind when reading these papers.

EDIT:

Just one more quick thought - my impression was that we've seen more than 0.2 to 0.3 degrees C anomaly in tropical SST's this year, but maybe that isn't true globally - not sure.

[donsutherland1]

X-y-no,

I believe Dr. Gray was referring to the long-term SST averages. This year--at least in the Atlantic--SSTs were at record warm levels as measured by the Tropical North Atlantic (TNA) Index. Given the ENSO region SSTs, the Pacific was probably reasonably close to somewhat warmer than the 30-year average.

I'll have to try to find Dr. Emmanuel's paper. It should make interesting reading. I expect more such papers in the years ahead and increasing debate, especially if a recent NASA study is reaffirmed by additional data from the years ahead.