Study says hurricanes growing more fierce
Global warming likely culprit in recent upswing

by Martin Merzer

Knight Ridder Newspapers

The accumulated power of Atlantic hurricanes has more than doubled in the past 30 years, with a particularly dramatic spike since 1995, and global warming likely is a major cause, according to a study to be published this week.

Though a connection between global warming and hurricane ferocity might seem logical, the report by a reputable climatologist at the Massachusetts Institute of Technology is the first to draw a statistical relationship between the two.

"The large upswing in the last decade is unprecedented and probably reflects the effect of global warming," scientist Kerry Emanuel wrote in a study that will appear in the Thursday edition of the journal Nature. Copies of the article were made available Sunday. However, his study did not shed any light on the effect, if any, of global warming on the number of storms.

But that is of only modest consolation. One reason: Scientists at the National Oceanic and Atmospheric Administration's hurricane research division in Virginia Key have concluded that, because of long-term natural cycles, we are in the middle of a decades-long period of more frequent hurricane formation. The current season, with a record seven named storms by July 23, provides unpleasant support for that conclusion.

Another source of concern: Most experts expect global warning to persist. So, if both camps of scientists are correct, we could be facing stronger storms and more of them - a potentially catastrophic collision of phenomena.

"My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential and - taking into account an increasing coastal population - a substantial increase in hurricane-related losses in the 21st century," Emanuel wrote. He said his analysis of wind-speed reports by the National Hurricane Center and other sources show that the accumulated power of hurricanes in the Atlantic basin, which includes the Caribbean Sea and the Gulf of Mexico, has more than doubled since 1970.

A particularly steep increase began in 1995, according to the study. "This large increase in power dissipation over the past 30 years or so may be because storms have become more intense, on the average, and/or have survived at high intensity for longer periods of time," he wrote. He said the trend is closely linked to an increase of about one degree in the average ocean surface temperature, which might not seem significant but can be crucial.

The 'smoking gun'?

"It sounds like a small amount, but we know that as waters get even a little bit warmer, the potential exists for hurricanes to get dramatically stronger," said Chris Landsea, an NOAA scientist on Virginia Key and one of the nation's leading hurricane researchers. Still, he is not fully convinced by Emanuel's study. Landsea said the 1995-04 spike in accumulated hurricane power correlated precisely with the beginning of the period of increased hurricane formation.

"It's very difficult to separate out what's caused by this natural cycle of activity versus man-made warming," Landsea said. He also raised concerns about some statistical procedures employed by Emanuel, whom he described as "a very respected researcher." "This is a serious study, and it needs to be taken seriously," Landsea said. "But when you take a close look at it, there's a lot of caveats. So, at this point, I'm not convinced he's found the smoking gun between global warming and hurricanes."

In October, Tom Knutson, a hurricane researcher at the government's Geophysical Fluid Dynamics Laboratory in Princeton, N.J., said he had noticed persistently high water temperatures in the main Atlantic hurricane zone. "The latest 10-year average is warmer than anything else in the record" dating to 1870, he said. "More research is needed to try to figure out how much of this is attributed to natural fluctuations and whether any of it is related to a broad-scale, global warming factor."

Knutson, who did not participate in Emanuel's study, co-wrote a report that was published in September and sparked new interest in the topic. It found that by the 2080s, global warming could cause the typical hurricane to produce 6 percent stronger winds and 18 percent more rain. In some cases, those winds could raise the average storm a half-step on the five-category Saffir-Simpson scale of hurricane intensity.

"There's some uncertainty, but we're saying that environmental conditions will support stronger hurricanes," Knutson said.

Mock experts wrong to link hurricanes with global warming
Jim O'Brien, My View

There is some disagreement among climate scientists on the potential impact of global climate change on future hurricanes in the Atlantic Ocean.

Last year claims were made that we will have more hurricanes due to global climate change. This was proven false. Currently it is said that hurricanes will be stronger in the future. There is no scientific support for either assertion.

In 2004, after Bonnie, Charley and Frances hit Florida, even the prime minister of England, Tony Blair, and many prominent American scientists told the world that the hurricanes were the result of global warming. Luckily scientists who actually study hurricanes quickly responded with the facts that global warming is not creating more hurricanes.

For once the scientists won this battle of misinformation. But now the alarmists are at it again, claiming that global warming will increase the intensity of hurricanes. Don't worry, readers: There is absolutely no correlation of hurricane intensity or hurricane frequency with global warming.

Scientists believe that variations in the Atlantic Ocean Conveyer - a virtual conveyer belt of ocean water, warm and cold - not global temperatures, determine the frequency of hurricanes. It is predicted that we will see an increase in the number of Atlantic hurricanes for the next 10 to 15 years compared to recent years. This has occurred before, from 1930 to 1970.

More specifically, that Atlantic Ocean Conveyer includes water in the North Atlantic that sinks to the bottom in winter and is replaced by warm Gulf Stream water of the South Atlantic, which leaves the North Carolina coast, moving northeast, on to Ireland and Norway. This oceanic phenomenon changes the sea surface temperatures. Subsequently, when it is strong, as between 1930 and 1970 and between 1995 and up to recent years, there are more Atlantic hurricanes when it is weak. Hurricane seasons were mild in those periods, specifically, from 1905 to 1925 and from 1975 to 1994.

As for intensity, hurricanes have to keep moving or they die by drawing the cold water from below the warmer sea surface water. For example, in 1998 Hurricane Mitch stalled off Honduras when it lost its upper atmospheric steering currents. It died and dropped more than 6 feet of rain on the poor folks in Honduras and Nicaragua. A hurricane will also grow stronger as it moves over water that's warmer than 80 degrees, and that's why some people believe that global warming will increase hurricane intensity.

There are, however, no scientific calculations that show an increase in the size of areas where the water is this warm. In fact, many of the stronger storms from warm areas, such as Africa, never make landfall. The forecasts for the 2005 hurricane season appeared in early June. They will be revised early this month. But no one expects Florida to encounter four hurricanes in 2005.

Nature is very variable and weather records are always being broken, but the reason is not global warming.