By: Dr. Jeff Masters , 12:33 PM GMT on July 24, 2007

The July 2007 issue of Scientific American has an article called "Warmer Oceans, Stronger Hurricanes" (referred to as "Warmer Water, SUPER HURRICANES" on the cover). The article is written by Dr. Kevin E. Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, and a lead author on the landmark 2007 climate report issued by the UN's Intergovernmental Panel on Climate Change (IPCC). The article makes the case that "evidence is mounting that global warming enhances a cyclone's damaging winds and flooding rains." The article presents some solid evidence to substantiate that point of view, which I will share below. However, I was disappointed in the general tone of the piece, which was over-hyped and did not paint an objective view of the current scientific thinking on the global warming/hurricane issue.

The hype
First off, the reader is hit with a dramatic full-page artist's depiction of the global super-hurricane of the future--a massive 5000-mile diameter Caribbean storm the size of North America. The storm's 200-mile eye is wider than the Florida Peninsula! Whoa, I said when looking at the whopper "SciAmicane". No doubt many readers perusing the magazine, trying to decide whether to buy it, had the same reaction and plunked down their $5 to read about this grim threat. OK, lets talk reality here. The largest tropical cyclone on record, Supertyphoon Tip of 1979, had a diameter of 1380 miles--less than one third the size of the SciAmicane. A storm like the SciAmicane cannot physically exist on Earth unless the oceans were to super-heat to about 122°F (50°C). Only an asteroid impact or similar calamity could create such a hypercane. Even the most extreme global warming scenarios do not heat the oceans to 122°, so the SciAmicane is there to sell magazines, not to illustrate what global warming might do to hurricanes.

Figure 1. Comparison of sizes: the Earth, the largest tropical cyclone on record (Supertyphoon Tip of 1979, 1380 miles in diameter), and the recently discovered hurricane-like vortex on Saturn (the Saturnicane). The "SciAmicane" is about the same size as the Saturnicane--5000 miles across.

The article also calls attention to 2004, when "an unprecedented four hurricanes hit Florida, and 10 typhoons made landfall in Japan". I've erroneously made this statement, too, but the truth is that Japan was hit by only four typhoons in 2004. Ten tropical cyclones that were of typhoon strength at some point during their life did hit, yes, but six of these had decayed to tropical storm or tropical depression strength by the time they hit Japan. The article then refers to a "consensus explanation" emerging to explain recent hurricane activity patterns, and "that explanation forebodes meteorological trouble over the long term." I'd say that the issue is still very much under dispute. In fact, the consensus statement on hurricanes and climate change adopted by the World Meteorological Organization in December 2006, in response to the recommendations of a panel of 125 hurricane researchers was thus: "Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point." Trenberth's article gives a list of four publications to read in the "more to explore" section, but none of these include the recent articles that call into question the strength of the global warming/stronger hurricane connection. (I apologize for not reviewing the many excellent articles that have appeared on this subject of late!)

The good science
There's quite a bit of good science in the article, which is worth reading if one keeps in mind its biases. In particular, I like the discussion of how global warming has affected precipitation and atmospheric water vapor. The 0.6°C (1.0°F) rise in Sea Surface Temperatures (SSTs) globally since 1970 has increased water vapor in the atmosphere by 4%, thanks to increased evaporation. This in turn has led to an 8% increase in global precipitation. Trenberth makes the point that no given hurricane can be blamed on global warming, but one can say 8% of a given storm's rainfall is due to global warming. There's also a nice discussion about how weaker than normal trade winds over the tropical Atlantic in 2005 caused less evaporational cooling than normal, allowing the ocean to heat to record temperatures. Finally, the conclusion of the article is one I certainly agree with:

We would all be wise to plan for more extreme hurricane threats.

Both theory and computer models predict a 3-5% increase in hurricane winds per degree C increase in tropical SSTs, and there is concern that the actual increase may be much more than this.

Jeff Masters

For a technical treatment of hypercanes, see Dr. Kerry Emanuel's paper, Hypercanes: a possible link in global extinction scenarios.

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2039. KoritheMan
11:00 PM CDT on July 25, 2007
Yeah that too mlc, thanks for clearing that up.
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2037. moonlightcowboy
3:58 AM GMT on July 26, 2007
Tropicdude, it's my understanding that when the Itcz comes up in latitude, it becomes easier for coriolis to take place with developing storms. JMHO

Good point, too, Kori...more latitude from the moisture in the Itcz would weaken the SAL. I need to post that one on my blog, thanks!
Member Since: July 9, 2006 Posts: 184 Comments: 29617
2036. KoritheMan
10:58 PM CDT on July 25, 2007
Bad news, tropicaldude. It not only washes out SAL, but allows more disturbances to develop, as well as tropical waves to ride along its axis. If a vigorous disturbance (like the one over Africa) can break free of the ITCZ, development can occur.
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2035. moonlightcowboy
3:56 AM GMT on July 26, 2007
Tropic'man...TAZ is a "favorite" hear on the blog and a good poster. We affectionately call it "Taz Speake"...so go easy, sometimes he just types too fast.

TAZ, you're too quick for us...lol. Hey, man, which one of these waves are gonna spin up first?
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2033. moonlightcowboy
3:54 AM GMT on July 26, 2007
Also, forgot to mention that over half of the Itcz in the Atlantic has been above 10n, some near Africa as high as 15n. Hasn't been that high all season that I can remember.
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2027. moonlightcowboy
3:49 AM GMT on July 26, 2007
Pardon me, Bama is right, shear is higher there, especially se of the wave, but tendency does relax further west. (my bad!)
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2026. Tazmanian
8:47 PM PDT on July 25, 2007
that wave most have a T # of 2.5 or 3.0 right now buy looking at this

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2025. benirica
3:49 AM GMT on July 26, 2007
lol michael
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2022. RL3AO
10:45 PM CDT on July 25, 2007
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2021. Tazmanian
8:43 PM PDT on July 25, 2007
LOL her the right one

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2020. benirica
3:43 AM GMT on July 26, 2007
ummm MARCH 06
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2017. RL3AO
10:43 PM CDT on July 25, 2007
TD298, I have a feeling that SSTs are not in the 60s and 70s in the GOM.
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2014. Tazmanian
8:39 PM PDT on July 25, 2007
wind shear map

wind shear is low for that wave about 1o to 15kt

i dont ues the cimss wind shear map be come it nevere tells you what you need to no her the map i like uesing

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2013. benirica
3:40 AM GMT on July 26, 2007
lol mlc i was about to light candles in your name if that actually happened and call my cousin over in texas to get out while she still can!
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2011. Rodek
3:37 AM GMT on July 26, 2007
Thanks TropicalMan07. I will lurk as much as possible over the next few days in order to watch this one. My goal is to learn a little and this wave may be a good teacher.
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2010. Bamatracker
3:39 AM GMT on July 26, 2007
if it keeps it identity till about 45-60W...it has a shot. Diffently wont hurt to watch it between times though....well im off to sleep...have a great night!!
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2009. RL3AO
10:38 PM CDT on July 25, 2007
The wave over Africa may be dead by the time it hits the ocean.
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2008. moonlightcowboy
3:36 AM GMT on July 26, 2007
LOL, Benerica, that's just a wild hunch, and not substantiated. Don't give it much credence!

ALSO, the wave that's already off the African coast is better in a few ways.

1. Already more convection
2. QScat already showing some rotation
3. Moisture plentiful and expanding further west because of help from previous waves.
4. Shear is a bit high, but tendency is relaxing

805 TWD:
Tropical wave will be introduced along 27w S of 17n moving W
about 15 kt. There are several indications of this wave. 1...a
weak signal is noted in the dakar sounding between 00z and 12z
on the 23rd. 2...a signal is noted in the sal sounding between
12z on the 24th and 00z on the 25th mainly in 850-900 mb level.
3...a 1946z Quikscat pass shows a weak circulation centered W of
the cape verdes near 13n27w. Scattered moderate convection is
from 12n-15n between 25w-28w.
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2007. Bamatracker
3:35 AM GMT on July 26, 2007

this link shows wind shear extremely high right off the coast.

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2005. benirica
3:32 AM GMT on July 26, 2007
im leaning towards bamatracker's side on this one, dont get over excited on this they always look impressive and just completely like a storm when over Africa but then they have to completely switch what they are and they never look the same...
not sure if im just making it up, but they have to transition from a land energy based system to a water energy based system
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2004. Bamatracker
3:34 AM GMT on July 26, 2007
not saying it wont ever develop...just going to take it a few days over the ocean before it has a chance to get its act together.
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2003. Rodek
3:32 AM GMT on July 26, 2007
Thanks Bama... That's the kind of info I was looking for. The water right off of Africa must be a heck of a barrier for a wave.
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2000. benirica
3:29 AM GMT on July 26, 2007
quite a prediction
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1998. Bamatracker
3:28 AM GMT on July 26, 2007
the waves always look real impressive over Africa. Then after they hit the water they tend to dissipate rather quickly..usually withing 24 hours. The sst's are still a bit cool in the eastern atlantic so the wave will have to wait until it gets further west before it has a legit chance to develop.
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1996. moonlightcowboy
3:27 AM GMT on July 26, 2007
Notice the heavy amount of moisture that has built back in off the African coast. The vapor field is also expanding further west, too!

I think we'll get an invest from either wave, CATL, or EATL with more moisture, adequate sst's and low shear.

There is more "updated" info on the current CV waves and SAL here.

Member Since: July 9, 2006 Posts: 184 Comments: 29617
1995. Rodek
3:25 AM GMT on July 26, 2007
My question of the nihgt:

Concerning the wave about to come off Africa, how is it's size/intensity compared to waves that actually generated a storm in the past?
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Dr. Masters (r) co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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