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| The graph from the US National Oceanic and Atmospheric Administration shows the active cycle of Atlanic hurricanes and says there are many more hurricanes, major hurricanes (79 vs 36) and hurricane landfalls in active hurricane periods. | |
BRIDGEOWN, Barbados, June 1, 2007 - Today is the official start of the Atlantic hurricane season and Professor Bill Gray says that global warming has no relevance on the increase in the number of hurricanes and storms he has predicted for this year.
"We have no plausible physical reasons for believing that Atlantic hurricane frequency or intensity will change significantly if global ocean temperatures continue to rise," Gray and his colleague Philip Klotzbach said in their forecast which was issued yesterday calling for 17 named storms, 9 hurricanes, and 5 intense hurricanes - no change over their May 3 pre-season forecast.
The two researchers from the Colorado State University dedicated an unusually large section of their forecast to dealing with the contentious global warming debate. It was not unexpected since Gray had been the focus of much criticism, some of it very acid and acrimonious, from sections of the scientific community because he stood in opposition to predictions by the Inter-governmental Panel on Climate Change (IPCC) and some fellow hurricane forecasters.
This year the IPCC, for the first time, has categorically linked global warming to an increase in hurricanes stating that there was an observational increase in the number of cyclones since 1970 in correlation to increased sea surface temperature. Caribbean meteorologists and consultants writing in Caribbean360 have agreed with the IPCC assessment and pointed out that more intense tropical cyclones have been reported in the past 15 years (1990-2005) than in the previous 15 years (1975-1989) with the greatest increases in the North Atlantic. They argued that the only contributing factor was global warming.
Gray maintains that they are wrong to link the two.
"Despite the global warming of the sea surface that has taken place over the last 3 decades, the global numbers of hurricanes and their intensity have not shown increases in recent years except for the Atlantic, where recent hurricane increases are likely a result of naturally occurring multi-decadal Atlantic Ocean circulation variations. The Atlantic has seen a very large increase in major hurricanes during the 12-year period of 1995-2006 (average 3.9 per year) in comparison to the prior 25-year period of 1970-1994 (average 1.5 per year)," he said.
Gray and Klotzbach said historical data does not confirm that the upsurge occurred only during global warming episodes.
"There have been similar past periods (1940s-1950s) when the Atlantic was just as active as in recent years. For instance, when we compare Atlantic basin hurricane numbers over the 15-year period (1990-2004) with an earlier 15-year period (1950-1964), we see no difference in hurricane frequency or intensity even though the global surface temperatures were cooler and there was a general global cooling during 1950-1964 as compared with global warming during 1990-2004."
They said that although global surface temperatures have increased over the last century and over the last 30 years, there was no reliable data available to indicate increased hurricane frequency or intensity in any of the globe's seven tropical cyclone basins, except for the Atlantic over the past twelve years.
"In a global warming or global cooling world, the atmosphere's upper air temperatures will warm or cool in unison with the sea surface temperatures. Vertical lapse-rates will not be significantly altered. We have no plausible physical reasons for believing that Atlantic hurricane frequency or intensity will change significantly if global ocean temperatures continue to rise. For instance, in the quarter-century period from 1945-1969 when the globe was undergoing a weak cooling trend, the Atlantic basin experienced 80 major (Cat 3-4-5) hurricanes and 201 major hurricane days. By contrast, in a similar 25-year period of 1970-1994 when the globe was undergoing a general warming trend, there were only 38 major hurricanes (48% as many) and 63 major hurricane days (31% as many) in the Atlantic basin. Atlantic sea-surface temperatures and hurricane activity do not necessarily follow global mean temperature trends."
US government forecasters at the National Oceanic and Atmospheric Administration (NOAA) when it issued its hurricane prediction just over a week ago steered clear from linking the increased numbers with global warming. They said that "climate patterns responsible for the expected above normal 2007 hurricane activity continue to be the ongoing multi-decadal signal (the set of ocean and atmospheric conditions that spawn increased Atlantic hurricane activity), warmer-than-normal sea surface temperatures in the Atlantic Ocean and the El Niño/La Niña cycle."
NUMBERS GAME
What appears to be playing out between the proselytes and the unbelievers is a numbers game.
The year 1995 saw an upsurge in hurricane activity in the Atlantic Ocean, shattering all records to become the most active season in the history of record keeping.
Those wanting to prove a statistical link with global warming include the 2005 numbers to compare to a previous lull period. For example they use the 15 year period of 1990-2005 as a benchmark to compare to the previous period of 1975-1989 while Gray pegs his 15-year period as 1990-2004 which would include 28 less storms.
Gray's argument however has been consistent over the years that the period between the 1960s-1990s was a lull cycle in Atlantic hurricane activity. Prior to 2005 he has consistently said at the annual National Hurricane Conference that this phase would end and be replaced by a cycle of high activity which would last for approximately 30 years.
FORECAST AND HURRICANE NAMES
Gray and Klotzbach have forecast 17 named storms which are expected to span 85 days; 9 hurricanes over 40 days and 5 intense hurricanes lasting 11 days.
Other hurricane forecasters have predicted similar numbers.
The names of the storms for 2007 are: Andrea (which formed in early May), Barry, Chantal, Dean, Erin, Felix, Gabrielle, Humberto, Ingrid, Jerry, Karen, Lorenzo, Melissa, Noel, Olga, Pablo, Rebekah, Sebastien, Tanya, Van, Wendy.
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