The incredible 2005 hurricane season, one of the deadliest and by far the most expensive on record, has inflamed worries about global warming.

Some of the country's most respected hurricane experts say it is impossible to indict global warming as the driving agent behind Katrina and the season's record numbers of storms.

A team of hurricane researchers has documented that tropical storms follow 25- to 40-year cycles in which busy periods alternate with lulls. These cycles are part of the Atlantic Multidecadal Oscillation (AMO).

The latest warm phase took hold in the mid-1990s. Right on schedule, an extraordinarily quiet hurricane period that began around 1970 ended abruptly in 1995. The last 11 seasons have wrought a level of activity unmatched in the era of reliable records.

What drives the oscillation?

These changes are far more subtle than the ones that could disrupt climate, but they are significant nonetheless.

The big question for researchers is whether the latest warm phase and the ferocity of the 2005 hurricane season got a charge from global warming.

They don't know. What they do know is that the cycle is far from over.

That is a chilling forecast, both for owners of coastal property and for taxpayers. Driven largely by hurricane damages, federal disaster expenses are off the charts.

Hurricane Katrina alone, blamed for hundreds of deaths and the biggest relocation in history, will cost every househould at least $100 in disaster expenses.

The Federal Emergency Management Agency has spent about $30 billion in direct disaster aid since 1995 - more than triple what it spent in the 40-year history of the program.