Recent studies have suggested a large, sudden increase in observed hurricane intensities. This increase has been linked to warming sea surface temperatures, which may in turn be associated with global warming. Theory and modelling predict that hurricane intensity should increase with increasing global temperatures, but work on the detection of trends in hurricane activity has focused mostly on their frequency.

Dr. Kerry Emanual of MIT argued that the potential destructiveness of hurricanes has increased markedly since the mid-1970s. This trend is due to both longer storm lifetimes and greater storm intensities. The hurricane power is correlated with tropical sea surface temperature. Future warming, Dr. Emanuel warned, may lead to an upward trend in hurricane destructive potential, and—taking into account an increasing coastal population—a substantial increase in hurricane-related losses in the twenty-first century.

In another study, Dr. PJ Webster and his colleagues at Georgia Tech examined the number of hurricanes and hurricane days over the past 35 years. A large increase was seen in the number and proportion of hurricanes reaching categories 4 and 5. The largest increase occurred in the North Pacific, Indian, and Southwest Pacific Oceans, and the smallest percentage increase occurred in the North Atlantic Ocean. The increases have taken place while the number of hurricanes and hurricane days has decreased in all basins except the North Atlantic during the past decade.

Over at the Live site, somebody stated, “On pg 452 of the July 28 Science, four authors, two from NOAA, conclude that some reports of a quick [span of two decades] increase in storm intensities is mostly a product of increasing precision of instrumentation and the bias in the old readings was toward an underestimation of storm intensity. Meteorology and climate studies are not my bailiwick so I could not refute their main claim: the uneven quality of the data gathered for tropical cyclones over the history of all such records in databases now used to seek trends probably makes the calculated trends an overstatement and reanalysis is in order.”

Actually, that’s a pretty good summary of the article. I downloaded a copy of the article, (“Can We Detect Trends in Extreme Tropical Cyclones?” by Christopher Landsea, Bruce Harper, Karl Hoarau and John Knaff), and think that the commenter at the Live site shouldn’t underestimate his or her abilities with meteorology and climate studies.

First of all, however, there is no particular reason to automatically refute the claims. Science is a legitimate, peer-reviewed forum for publication of scientific research, and any paper published therein has already been through a vigorous examination, and will be open to future comment and questioning by the scientific community.

In fact, the mere existence of this paper in a peer-reviewed, scientific journal refutes the claim that those who don’t unquestioningly adhere to every premise of global climate change are censored and excluded from the scientific literature. Science is as mainstream a scientific journal as they get and it has published numerous articles on the science of global warming, and yet here’s a paper skeptical of the reported trend of increasing hurricane intensity. Go figure.

Of course, the paper does not actually refute, or even question, sea temperature increases in particular or global climate change in general, like virtually the entirety of the peer-reviewed literature on the subject. It merely poses an interesting argument that holds that the record of hurricane intensity during the period of 1970 to 1990 is not as reliable as the post-1990 record, and that it's possibly biased away from extreme events. Therefore, any analyses of trends in global hurricane intensities should be undertaken with this in mind.

Nonetheless, the press has jumped on the paper and are sensationalizing it as a refutation of the entire science of climate change. “If Dr. Landsea and his co-authors are correct,” the Associated Press reported, “the previous studies are fundamentally flawed.” Dr. Landsea told the AP, “The methodology is fine. There’s no problem with the way they analyzed the data. The problem is with the data itself.”

However, all that Dr. Landsea and company have questioned was whether the global databases are of sufficient reliability to ascertain long-term trends in hurricane intensity, particularly for extreme events (categories 4 and 5 on the Saffir-Simpson Hurricane Scale).

The argument seems reasonable. The main method used for estimating hurricane intensity derives from a satellite-based pattern recognition scheme known as the Dvorak Technique. However, the Dvorak Technique does not directly measure maximum sustained surface wind. Even today, application of this technique is subjective, and it is common for different forecasters and agencies to estimate significantly different intensities on the basis of identical information.

The Dvorak Technique was invented in 1972 and was soon used by U.S. forecast offices, but the rest of the world did not use it routinely until the early 1980s. Until then, there was no systematic way to estimate the maximum sustained surface wind for most hurricanes. And since the Dvorak Technique was first developed for visible imagery, it precluded obtaining intensity estimates at night and limited the sampling of maximum sustained surface wind.

In 1975, only two geostationary satellites were available for global monitoring. Today, eight satellites are available, with far greater resolution. The higher resolution images and more direct overhead views of hurricanes result in greater and more accurate intensity estimates in recent years when using the Dvorak Technique.

For example, Atlantic Hurricane Hugo was estimated to have a maximum sustained surface wind of 59 meters/second on September 15, 1989 based on use of the Dvorak Technique. But aircraft reconnaissance data obtained at the same time revealed that the hurricane was much stronger (72 meters/second) than estimated by satellite. This type of underestimate was probably quite common in the 1970s and 1980s in all basins because of application of the Dvorak Technique in an era of few satellites with low spatial resolution.

The 1970 Bangladesh cyclone - the world’s worst tropical-storm disaster, with 300,000 to 500,000 people killed - does not have an official intensity estimate, despite indications that it was extremely intense. Inclusion of this and similar storms as extreme events would boost the frequency of such events in the 1970s and 1980s to numbers indistinguishable from the past 15 years, suggesting no systematic increase in extreme tropical cyclones for the North Indian basin.

These examples are not likely isolated exceptions. Reanalysis of satellite images in the Eastern Hemisphere basins suggest that there are at least 70 additional, previously unrecognized category 4 and 5 hurricanes during the period 1978-1990. The pre-1990 tropical hurricane data for all basins are replete with large uncertainties, gaps, and biases. Trend analyses for extreme events are unreliable because of operational changes that have artificially resulted in more intense hurricanes being recorded, casting severe doubts on any such trend linkages to global warming.

Scientific acceptance of the basis for global warming does not mean unquestioning acceptance of every claim, every theory and every idea made. A truly scientific approach would be one of intense questioning and inquiry, sort of like the practice of Zen.