In a June 25 Washington Post op-ed headlined “Gloom and Doom in A Sunny Day,” Slate.com contributing writer Emily Yoffe wrote that former Vice President Al Gore “and others say that [Hurricane] Katrina was a product of global warming and that we can expect more and bigger storms. But there is actually brisk scientific debate over the role global warming plays -- if any -- in the creation of hurricanes.” In fact, while Gore reported in his book An Inconvenient Truth (Rodale Books, May 2006) that “less than a month before Hurricane Katrina hit the United States a major study from MIT supported the scientific consensus that global warming is making hurricanes more powerful and destructive,” he did not claim that Katrina itself was a “product” of global warming. In fact, just two weeks after Katrina made landfall in New Orleans, Gore gave a speech before the National Sierra Club Convention in San Francisco on September 9, 2005, saying:

Here's what I think we here understand about Hurricane Katrina and global warming. Yes, it is true that no single hurricane can be blamed on global warming. Hurricanes have come for a long time, and will continue to come in the future. Yes, it is true that the science does not definitively tell us that global warming increases the frequency of hurricanes -- because yes, it is true there is a multi-decadal cycle, twenty to forty years that profoundly affects the number of hurricanes that come in any single hurricane season. But it is also true that the science is extremely clear now, that warmer oceans make the average hurricane stronger, not only makes the winds stronger, but dramatically increases the moisture from the oceans evaporating into the storm -- thus magnifying its destructive power -- makes the duration, as well as the intensity of the hurricane, stronger.

Further, during his March 21 testimony before the House Committee on Energy and Commerce Gore stated:

There is no consensus linking the frequency of hurricanes to global warming and I've never said there is -- it's the intensity of hurricanes. It's also true, the scientists say, you can't take an individual storm and say, “This is caused by global warming.” But the odds of stronger storms are going up.

Moreover, Gore's assertion in his book that global warming may be linked “to a significant increase in both the duration and intensity of hurricanes” is supported by the 2007 Intergovernmental Panel on Climate Change (IPCC) report, which concluded that "[b]ased on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs [sea surface temperatures]." [Emphasis in original.]

From the IPCC report:

Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs. There is less confidence in projections of a global decrease in numbers of tropical cyclones. The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period.

In the op-ed, Yoffe wrote:

Recall that the experts told us last year would be a record-setting hurricane season, but the series of Katrinas never materialized.

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It's also hard to believe assertions that the science on the future of our climate is settled when climate scientists can't agree about the present -- or the past (there is contention about the dates, causes and even the existence of the Medieval Warm Period and the Little Ice Age that followed). Now, Gore and others say that Katrina was a product of global warming and that we can expect more and bigger storms. But there is actually brisk scientific debate over the role global warming plays -- if any -- in the creation of hurricanes.

In his book, Gore attributed the claim “that global warming is even leading to an increased frequency of hurricanes” to “some” scientists. However, he also acknowledged that "[t]here is less agreement among scientists about the relationship between the total number of hurricanes each year and global warming." From the book (Page 81):

A growing number of new scientific studies are confirming that warmer water in the top layer of the ocean can drive more convection energy to fuel more powerful hurricanes.

There is less agreement among scientists about the relationship between the total number of hurricanes each year and global warming -- because a multi-decade natural pattern has a powerful influence on hurricane frequency. But there is now a strong, new emerging consensus that global warming is indeed linked to a significant increase in both the duration and intensity of hurricanes.

Brand-new evidence is causing some scientists to assert that global warming is even leading to an increased frequency of hurricanes, overwhelming the variability in frequency long understood to be part of natural deep-current cycles.

In the update to the film Gore said: “There is no scientific consensus linking the absolute number of hurricanes to global warming.” From the update:

GORE: In the year that has passed by since the end of filming An Inconvenient Truth, there have been several brand-new scientific studies that have further firmed up the emerging consensus that links stronger hurricanes with higher ocean temperatures, particularly higher temperatures in the top layer, the top 200 feet, where the heat energy drives strength into these ocean-based storms. There is no scientific consensus linking the absolute number of hurricanes to global warming. There's some indication that on a worldwide basis, the number stays fairly steady. But when hurricanes do form out of these delicate and mysterious atmospheric conditions in the oceans, then global warming makes them stronger. And, when they get stronger with more moisture, they become more destructive.

In support of her claim that “there is actually brisk scientific debate over the role global warming plays -- if any -- in the creation of hurricanes,” Yoffe wrote:

A study from the Woods Hole Oceanographic Institution [WHOI] last month, looking at 5,000 years of Atlantic hurricanes, found “large and dramatic fluctuations in hurricane activity, with long stretches of frequent strikes punctuated by lulls that lasted many centuries” -- with the stormier periods occurring during cooler ocean temperatures. But talking about Earth's constant, and still inexplicable, climate changes and cycles is not useful if you're trying to shock.

Although the WHOI study's news release does report that the authors “found large and dramatic fluctuations in hurricane activity, with long stretches of frequent strikes punctuated by lulls that lasted many centuries,” it does not appear to contradict Gore's assertion that "[a] growing number of new scientific studies are confirming that warmer water in the top layer of the ocean can drive more convection energy to fuel more powerful hurricanes." Rather, it states: "[I]ndeed, warmer sea surface temperatures provide more fuel for the formation of tropical cyclones." From the WHOI news release:

Much media attention has been focused recently on the importance of warmer ocean waters as the dominant factor controlling the frequency and intensity of hurricanes. And indeed, warmer sea surface temperatures provide more fuel for the formation of tropical cyclones. But the work by Donnelly and Woodruff suggests that El Niño and the West African monsoon appear to be critical factors for determining long-term cycles of hurricane intensity in the Atlantic.