Holland told a packed hall at the American Meteorological Society's 27th Conference on Hurricanes and Tropical Meteorology that the wind and warmer water conditions that fuel storms that form in the Caribbean are "increasingly due to greenhouse gases. There seems to be no other conclusion you can logically draw."

His conclusion will be debated throughout the week-long conference, as other researchers present opposing papers that say changing wind and temperature conditions in the tropics are due to natural events, not the accumulation of carbon dioxide emissions clouding the Earth.

Many of the experts gathered in the coastal city of Monterey, California, are federal employees. The Bush administration contends global warming is an unproven theory.

While many of the conference's 500 scientists seem to agree that a warming trend in the tropics is causing more and stronger hurricanes than usual, not all agree that global warming is to blame.

Some, like William Gray, a veteran hurricane researcher at Colorado State University in Fort Collins, Colorado, attributed the warming to natural cycles. Gray said he believes salinity buildups and movements with ocean currents cause warming and cooling cycles. He predicted the Caribbean water will continue to warm for another five to 10 years, then start cooling.

MORE WARMING TO COME

Whatever the cause, computer projections indicate the warming to date -- about one degree Fahrenheit (half a degree Celsius) in tropical water -- is "the tip of the iceberg" and the water will warm three to four times as much in the next century, said Thomas Knutson, explaining projections from the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey.

Adam Lea, a postdoctoral student at Britain's University College London in Dorking, Surrey, presented research based on British, German, Russian and Canadian studies that concludes half of the increased hurricane activity in the tropics could be attributed to global warming.

Holland, director of the Mesoscale and Microscale Meteorology Division of the federal research center, said tropical storm anomalies in the 1940s and 1950s can be explained by natural variability.

But he said carbon dioxide started changing traceable patterns in the 1970s and by the early 1990s, the atmospheric results were affecting the storm numbers and intensities.

"What we're seeing right now in global climate temperature is a signature of climate change," said Holland, a native of Australia. "The large bulk of the scientific community say what we are seeing now is linked directly to greenhouse gases."

Hurricane Katrina, which tore onto the Louisiana and Mississippi coasts on Aug. 29, was the deadliest Atlantic hurricane in 77 years and the costliest ever, with property damages estimated at US$75 billion.