Gray's Hypothesis Doesn't Hold Water

The author of today’s post, Bill Chameides, Ph.D., is Chief Scientist at Environmental Defense.

This morning, the Wall Street Journal published an Op-Ed by Dr. William Gray titled "Hurricanes and Hot Air". In it, Dr. Gray argues that there is no link between global warming and the recent "increase in major hurricanes".

Unfortunately, this piece has several inaccuracies and omissions. Let me clear them up.

Dr. Gray makes three fundamental errors. First he says that "warming theorists" think global warming has increased the number of hurricanes since 1995. Actually, the studies indicate a link between warming water and stronger storms, not number of storms. Moreover, the increase is apparent since the 1970s, not just since 1995. Gray is certainly free to critique the research, but he shouldn’t misrepresent what the research indicates.

Second is his argument that hurricane frequency has increased because of a "the speed-up of water circulating in the Atlantic Ocean" (called the thermohaline circulation, or THC). The problem with this conclusion is that the THC has not accelerated. In fact, a recent study indicates that the THC may have decreased 30 percent over the past 50 years.

But because observations of this large-scale phenomenon are just beginning to come in, the conservative scientific consensus is that there is still "no coherent evidence for a trend" in the THC (see Box 5.1, page 397 in Chapter 5 of the IPCC report). Either way, it’s clear that Gray’s hypothesis just doesn’t hold water.

Gray’s third erroneous claim is that scientists studying the relationship between hurricanes and global warming "rely more on theory than on observation". In fact, most recent studies of the link between global warming and hurricanes are based on data. There’s a good summary of all the recent papers, including those by Dr. Gray and his colleagues, on our Web site.

The first study to indicate a link between global warming and hurricane intensity was based on actual measurements of sea surface temperature and hurricane intensity in the North Atlantic and North Pacific. The relationship was clear: the warmer the water, the stronger the storm. Starting in about 1975, sea surface temperatures began to increase dramatically, and the destructive potential of hurricanes followed suit.

Water Temperature and Storm Strength

The solid line shows the destructive potential of North Atlantic and North Pacific hurricanes; the dotted line shows average sea surface temperature in the two hurricane regions. Source: Figure 3 in Emanuel, 2005 [PDF].

Subsequent studies looked at all six hurricane basins – not just the Atlantic – and also found that storms have gotten stronger as the water has gotten warmer. One study showed that the number of Category 4 and 5 hurricanes almost doubled over the past 30 years.

Number of Intense Hurricanes

Percent of Intense Hurricanes

Source: Figure 4 in Webster et al, 2005 [PDF].

These measurement-based studies show a strong and real relationship between sea surface temperature and hurricane strength. They also indicate that warming water is producing stronger storms all over the world, not just in the Atlantic. That’s an important point to remember, since global warming is, well, a global phenomenon.

Unfortunately for those affected by hurricanes (and despite Dr. Gray’s claims to the contrary), the best available scientific evidence is that global warming due to human activities is contributing to the recent increase in storm strength.

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  1. Posted July 27, 2007 at 12:06 pm | Permalink

    Hey there,

    Someone just commented on our site ( that Climate 411 was a great resource and I couldn’t agree more, this is amazing content.

    Would be great to swap links on blogrolls, so all our readers can be directed to your blog.

    Let me know. Drop a line at desmogblog[at]


  2. Eddie
    Posted July 27, 2007 at 9:27 pm | Permalink

    I’ve been reading Climate 411 for months, and really appreciate how it takes complicated science and distils into highly readable posts without too much dumbing down. Great job, Bill!

    One thing I don’t understand: What’s the “411” stand for?

  3. Anonymous
    Posted July 28, 2007 at 8:30 pm | Permalink

    The Global Warming “Movement” is the new home of the “Nuclear Freeze”—anti-capitalist group of Marxists. This is obvious.

  4. aaron burton
    Posted July 29, 2007 at 3:14 pm | Permalink

    Do these anti-capitalists include the USCAP (United States Climate Action Partnership) whose members include GM, GE, Pepsi, and several other major corporations?

  5. Anonymous
    Posted July 29, 2007 at 10:13 pm | Permalink

    But how do these studies linking warmer temps to stronger storms take into account improvements in measurement and just the fact that there are more people living more expensive lifestyles near coasts than ever before?

    I think that when we look to these factors, we find that the link between warmer temperature and stronger storms isn’t really there, because we can’t be certain that the storms are stronger. They may be causing more damage than past storms, but that is because there is more to destroy.

    The hurricane link is too much of a stretch, we need to stick to the battles that can be won and stop risking losing support because we make claims that cannot be backed up by good science.

  6. Posted July 29, 2007 at 11:48 pm | Permalink

    I dont have a web site, myself, but the folks at that site I punched in above do and boy to they get it… Want to learn how much of a crock this global warming thing is? Go there.

    As for this site, well, please… Stop insulting our intelligence. The first chart shows two series on it. One is a “potential” value and the other is an “actual” value. Thats not very credible at all. If it were “actual vs actual” then it would hold water.

    It would also be nice to see the up-to-date data for the 2nd and 3rd sites, but that would destroy those graphs’ integrity. A nil hurricane season in 2006 and thus far 2007 is shaping up to be identical. You wouldnt have a very effective campaign for global warming with the past 2 years data in it. And, why are we talking about data from the 1970s, on? I mean, the planet has been around 4.5 BILLION years and we’re discussing data (when its in its entirety) of what? 30 years? Some talk about 150 years and others MAYBE 18,000 years IF we are lucky?

    Come on folks, get real. Unless you people KNOW for sure – the rest of us arent believing diddly from you.

    Since none of this adds up, and since THAT is the basis of this fear-uncertainty-doubt campain, global warming is STILL nothing more than a theory.

    Americans have had enough of paying for “theories”. The more we ignore the REAL problems facing our planet (crime of all sorts, lack of enforcement, children dropping out of school at a rate of 25-30%, and more) then those problems will continue to go unchecked and froo-froo issues will be given the spot-light.

  7. Anonymous
    Posted July 30, 2007 at 10:54 am | Permalink

    That site you “punched in above” is totally bogus. It’s just a bunch of amateur hacks ( a writer and software developer ) publishing all the right wing bogus misinformation they can find. My guess to make a little side money publishing Google ads.

    Calling it a discussion is laughable at best.

  8. Posted July 30, 2007 at 3:12 pm | Permalink

    > One thing I don’t understand: What’s the “411” stand for?

    “Information”. You know, you want a telephone number you dial 411 for Information? :)

  9. Posted July 30, 2007 at 4:37 pm | Permalink


    Thanks for you questions, here are my responses.

    1. The fact that more people now live on or near the coast has no bearing on whether storms have become more intense, or whether the increased intensity is related to sea surface temperature. In fact, the vast majority of storms – including those analyzed in the studies cited in my post – never make landfall.

    2. The improvement-in-measurements issue that you raise was discussed in the post. In brief, some have suggested that the finding that storm intensity has increased over the past few decades is an artifact caused by inaccurately classifying storms before 1990. However, a paper by Fasullo suggests that this is a non-issue. See .

    3. As for your statement that, “The hurricane link is too much of a stretch, we need to stick to the battles that can be won.” What can I say? I call them as I see them. I find the data linking hurricane intensity and increased sea surface temperatures compelling.

  10. Posted July 30, 2007 at 6:00 pm | Permalink

    Hey, Discuss Global Warming. I’m always a little surprised when I get posts like yours – a lot of anger. I’m just a scientist reporting the facts as I see them. Sorry if the facts upset you. Anyway, here are my responses.

    “Destructive potential” is an index comprised of actual measurements of a storm’s wind speed and duration. Together these give an idea of how much damage the storm has the potential do it.

    Including 2006 and 2007 in the figures would not affect the conclusion. Climate is the average weather pattern of a region over many years. Changes that occur over a few years cannot prove or disprove a climate trend.

    Yes, the planet is 4.5 billion years old and has changed on geologic time scales, but that doesn’t mean that the current climate change is also naturally induced. This type of logical error is called Igoratio Elenchi, or “irrelevant conclusion”.

    Also, climate change today has an impact it didn’t have billions of years ago. Today there are 6 billion people on Earth.

    As for “knowing for sure”… We take action based on probabilities all the time. You fasten your seat belt when you get into a car, don’t you? We just did a post on scientific uncertainty. Take a look – I think you’ll find it interesting.

    And yes, the world has many problems that must be addressed, but it’s not an either or proposition. Addressing global warming doesn’t mean ignoring all other issues.

  11. Posted August 2, 2007 at 2:45 am | Permalink


    How many years of lower-than-usual hurricane activity does it take to count? Seems that every year we have more-than-usual activity we hear cries of “human-caused global warming” from every corner, yet in slower years scare-mongers divert attention to other natural “crises” like fires in California, drought in the south, floods in the southwest…something. Anything to keep people frightened.

    Personally, I think it’s Henny-Penny.

    But you’re slick. If we start having rough winters again like the 70s, you’ll change tactics, adjust your bio, and find another way to profit, gain notoriety, and promote socialism.

    Why don’t we who love the environment do something worthwhile, like clean up our rivers, promote nuclear energy, preserve more land for wildlife, promote better waste management, etc. instead of this Henny-Penny nonsense? Let’s insist on clean air for the sake of beauty and health—not for the sake of unproven theories and Al Gore’s wallet. If (read: “When”) human-caused global warming is proven false, the real potential exists for mass discrediting of those in the scientific community who cried wolf. IT WILL HURT THE CAUSE OF CONSERVATION as Americans will sense they’ve been burned. And you will be an active coconspirator.

    Just wondering, what role does the sun play in our global warming crisis? I read the Russian scientist, Illarionov, who according to the Harvard University Gazette,

    “question[s] the science behind global warming, saying that the impact of human-caused carbon dioxide emissions on the global climate has not been proved. He cited normal variations in the sun’s strength as a major driver of the Earth’s climate and said the Earth’s temperature has a long, natural, history of rising and falling. In fact, Illarionov said, the Earth’s temperature in many places appears to be cooling, not warming.”

    BTW, I first found this website because of the completely irresponsible commercial that had the little girl being hit by the train (implied). When those nutcases on the right pull that kind of stunt we crucify them. I smell hypocrisy.