The number of hurricanes in the most powerful categories -- like Katrina and Andrew -- has increased sharply over the past few decades, according to a new analysis sure to stir debate over whether global warming is worsening these deadly storms.
While studies have not found an overall increase in tropical storms worldwide, the number of storms reaching categories 4 and 5 grew from about 11 per year in the 1970s to 18 per year since 1990, according to a report in Friday's issue of the journal Science.
Peter Webster, of the Georgia Institute of Technology, said it's the warm water vapor from the oceans that drives tropical storms, and as the water gets warmer the amount of evaporation increases, providing more fuel for the tempests. Between 1970 and 2004 the average sea surface temperature in the tropics rose nearly 1 degree.
PHOTO: AP
Co-author Greg Holland of the National Center for Atmospheric Research said the researchers can't say rising sea-surface temperatures caused Hurricane Katrina. But their study shows the potential for more Katrina-like events to occur, he said.
Katrina was a category 5 storm at sea and was category 4 when it made landfall. The increase in storms they found is for category 4 and 5. Category 4 storms have wind speeds of 211kph to 249kph and Category 5 is for storms with sustained winds of 251kph and over.
Co-author Judith Curry of Georgia Tech said the team is confident that the measured increase in sea surface temperatures is associated with global warming, adding that the increase in category 4 and 5 storms ``certainly has an element that global warming is contributing to.''
There is a natural variability of the climate and some would interpret the changing number of storms to be part of that variability, Holland said. But the variability in the past has been over 10-year periods, and this is sustained over 30 years.
Webster added that sea surface temperatures ``are rising everywhere in the tropics and that is not connected to any natural variability we know.''
In their analysis of hurricanes -- known as typhoons or cyclones in other parts of the world -- the researchers counted 16 category 4 and 5 storms in the Atlantic-Caribbean-Gulf of Mexico from 1975 to 1989. This increased to 25 in the 1990 to 2004 period.
In the eastern Pacific the increase was from 36 to 49 storms and it went from 85 to 116 in the western Pacific. In the southwest Pacific the increase was from 10 to 22 powerful storms, while the total went from one to seven in the north Indian Ocean and from 23 to 50 in the south Indian Ocean.
Kerry Emanuel, a climatologist at Massachusetts Institute of Technology, reported in August in the journal Nature that hurricanes in both the Atlantic and Pacific have increased in duration and intensity since the 1970s.
While the new study looks at the problem differently, ``we are clearly seeing the same signal in the data,'' Emanuel said.
But other researchers were cautious.
Christopher Landsea, a meteorologist at the National Oceanic and Atmospheric Administration's Hurricane Research Division in Miami, questioned the data showing an increase in major storms, saying the estimates of the wind speed in storms in the 1970s may not be accurate.
The study looked at storms worldwide, and ``for most of the world there was no way to determine objectively what the winds were in 1970,'' he said. The techniques used today were invented later and infrared satellite studies weren't available until the 1980s, Landsea said.
The Atlantic-Caribbean-Gulf of Mexico region is the best monitored in the world and that region had the smallest increase, he noted.
``This really highlights the need to go back and get all the original data ... and reanalyze the storms with today's
techniques,'' Landsea said in a telephone interview. ``These are billion-dollar questions and we need to better answer them.''
Holland agreed there have been changes in the observing system since the 1970s but noted the increase has been steady over the period, ``it didn't just kick in when the new measurement methods kicked in.''
The fact that the trend is smaller in the Atlantic basin is beside the point, he added, because it has gone up there too.
``The end result is that there is no doubt that there is a substantial increase here,'' Holland said.
Roger Pielke, director of the Center for Science and Technology Policy Research at the University of Colorado, said the report ``reinforces the view that we should pay even greater attention to preparing for the inevitability of future intense hurricanes striking vulnerable locations around the world. In the context of ever-growing coastal development, the costs of hurricanes are going to continue to escalate.''
Emanuel, Landsea and Pielke were not part of Webster's research team. Webster's research was funded by the National Science Foundation and the National Center for Atmospheric Research.
A few weeks ago I found myself at a Family Mart talking with the morning shift worker there, who has become my coffee guy. Both of us were in a funk over the “unseasonable” warm weather, a state of mind known as “solastalgia” — distress produced by environmental change. In fact, the weather was not that out of the ordinary in boiling Central Taiwan, and likely cooler than the temperatures we will experience in the near-future. According to the Taiwan Adaptation Platform, between 1957 and 2006, summer lengthened by 27.8 days, while winter shrunk by 29.7 days. Winter is not
Taiwan’s post-World War II architecture, “practical, cheap and temporary,” not to mention “rather forgettable.” This was a characterization recently given by Taiwan-based historian John Ross on his Formosa Files podcast. Yet the 1960s and 1970s were, in fact, the period of Taiwan’s foundational building boom, which, to a great extent, defined the look of Taiwan’s cities, determining the way denizens live today. During this period, functionalist concrete blocks and Chinese nostalgia gave way to new interpretations of modernism, large planned communities and high-rise skyscrapers. It is currently the subject of a new exhibition at the Taipei Fine Arts Museum, Modern
March 25 to March 31 A 56-year-old Wu Li Yu-ke (吳李玉哥) was straightening out her artist son’s piles of drawings when she inadvertently flipped one over, revealing the blank backside of the paper. Absent-mindedly, she picked up a pencil and recalled how she used to sketch embroidery designs for her clothing business. Without clients and budget or labor constraints to worry about, Wu Li drew freely whatever image came to her mind. With much more free time now that her son had found a job, she found herself missing her home village in China, where she
In recent years, Slovakia has been seen as a highly democratic and Western-oriented Central European country. This image was reinforced by the election of the country’s first female president in 2019, efforts to provide extensive assistance to Ukraine and the strengthening of relations with Taiwan, all of which strengthened Slovakia’s position within the European Union. However, the latest developments in the country suggest that the situation is changing rapidly. As such, the presidential elections to be held on March 23 will be an indicator of whether Slovakia remains in the Western sphere of influence or moves eastward, notably towards Russia and