The ferocity of last year's season gave ammunition to a growing chorus of voices that says humans and their greenhouse gas-spewing cars and factories could be making hurricanes more destructive.

But it did nothing to convince a hard core of hurricane researchers who insist there's no evidence that people are responsible for the recent intensity, and growing number, of tropical cyclones.

The stakes are high. An estimated 50 million people live along the hurricane-vulnerable US east and Gulf coasts.

Millions more live in flood-prone mountains in Haiti and Central America, where hurricanes take thousands of lives.

The US hurricane tab last year was more than US$100 billion. Major storms in the 2004 season caused another US$45 billion in damage.

"The coastal regions are in jeopardy. The Miami area and the New Orleans area are very much at risk. We have a 10-year window to do something about greenhouse gases," said Professor Judith Curry, chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.

"STUNNING INCREASES"

Curry said leading scientists with published research have compelling evidence that human-induced global warming is heating the seas from which hurricanes draw their strength. In the North Atlantic -- as the Atlantic north of the equator is called -- that has increased both the number and intensity of hurricanes in the last decade, she said.

"They are stunning increases that are way outside the bounds of natural variability," she said.

Tropical ocean temperatures have risen about one degree Fahrenheit since 1970, said Curry. "This one degree is playing havoc with hurricanes. It's a lot of extra energy for these storms."

When Wilma's internal pressure hit 882 millibars, beating a record held by 1988's Gilbert, climatologists took notice. It was the first time a single season had produced four Category 5 hurricanes, the highest stage on the 5-step Saffir-Simpson scale of storm intensity.

The 28 tropical storms and hurricanes crushed the old mark of 21, set in 1933.

While some hurricane researchers accept that the sea is warming, they believe it's part of a natural cycle, rather than caused by humans.

They say the Atlantic entered a period of heightened hurricane activity around 1995 and may not settle down for another 20 or 30 years due to a cycle called the "Atlantic multidecadal oscillation."

With hurricane records for only 150 years, some say there isn't enough historical data to blame the greenhouse effect.

"We don't have any facts because we don't have any long-term records," said Neil Frank, a former director of the US National Hurricane Center.

The debate has taken center-stage among hurricane and climate scientists in the United States, where President George W. Bush's rejection of the Kyoto agreement to cut greenhouse gases enraged environmental groups and foreign nations.

Some US scientists say Washington has stifled dissenters. Others deny it. "No one has put any pressure on me, from the White House or anywhere else," US National Hurricane Center director Max Mayfield said.

GROWING EVIDENCE

After two of the worst seasons on record -- 2004 produced 15 storms -- US researchers are speaking more boldly.

At an American Meteorological Society conference in Monterey, California, last week, a US government researcher blamed last year's record season on global warming.

On the Web site of the government's Geophysical Fluid Dynamics Laboratory, the subject is broached frankly.

"The strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases....," it says.

Kerry Emanuel, a professor at the Massachusetts Institute of Technology, wrote in Nature magazine last August that the power dissipated by hurricanes in the North Atlantic has doubled in the last 30 years, possibly because storms have been more intense for longer periods of time.

"My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential," he wrote.

A study by Curry and her colleagues published in Science magazine last autumn found the proportion of hurricanes reaching Category 4 and 5 has nearly doubled in the last 35 years.

But Frank, the former hurricane centre director who now is a weatherman for KHOU television in Houston, said he does not believe hurricanes are more frequent or more intense than they were in the last warming period, in the 1930s, '40s and '50s.

Only since the 1970s have researchers had satellites that allow them to look directly at hurricanes. As a result, he believes, storms that might have escaped detection in mid-ocean decades ago are now tracked from birth to death.

Scientists who believe human-induced global warming is linked to hurricane formation and strength rely too heavily on numerical models, Frank said.

"These same numerical models that I can't put faith in for a two-week forecast, we're told can be accurate out 200 years," he said. "Ridiculous."

Whatever the outcome of the debate, forecasters say the damaging seasons of 2004 and 2005 could be just the beginning.