Watching storm after powerful storm plow into the U.S. coastline this year, I can't help wondering if the world's weather is actually trying to tell us something. Perhaps it was only coincidence that Hurricane Frances was covering the whole of Florida with blinding winds and torrential rains just as George W. Bush climbed the podium in New York to speak to the Republican National Convention (while poor brother Jeb was forced to stay home in Tallahassee). But to someone like me, who has been tracking global warming and its effects around the world for several years, it almost seemed as though the storm was trying to deliver a forceful reminder of the reality of climate change and the need to act now to address it.

The intensity of this storm season has brought the issue of global warming to many minds. And with reason. So far, 2004 has been an extraordinarily potent one for hurricanes. But how much of it is due to global warming?

Let's look at the facts. Despite a late start to the season, the total of eight tropical cyclones (the catchall term for low-pressure systems over tropical waters) reaching tropical storm or hurricane strength last month set a new August record -- the average is four for that stage in the season. The run of storms has continued unabated into September. Hurricanes are essentially heat engines, forming over warm ocean waters and gaining strength from the latent heat released as evaporated water from the sea surface condenses and falls back to Earth in the form of pounding tropical rain. This released heat drives rapid updrafts that cause more water to evaporate from the ocean surface and form a self-reinforcing vortex of swirling clouds generating wind speeds, as in Hurricane Ivan's case, of up to 160 miles per hour.

Buried deep in the Web site of the National Oceanic and Atmospheric Administration (NOAA) is a graph that shows how tropical Atlantic sea surface temperatures have steadily risen between 2000 and 2004. NOAA classifies all but one of these hurricane seasons as "above normal" -- the exception is 2002, which suffered the hurricane-suppressing influence of a weak El Nino, the warm-water current that occasionally crosses the Pacific Ocean from west to east. To many, this suggests a global warming fingerprint: The accumulation of greenhouse gases -- principally carbon dioxide -- has driven world temperatures to new heights (2002 and 2003 tied for second place after 1998 as the warmest years ever). The seas are slowly heating up, too, providing more energy for tropical storms.

Case closed? Not quite. The true picture is actually a good deal more complex. Oceanic heat is just one factor favoring stronger and more numerous storms this year. Another is lower levels of so-called "wind shear" -- horizontal winds that can chop storms in half and prevent them from intensifying. And historically speaking, a busy hurricane season may not be so unusual. The mid-1920s through the 1960s were very active, whereas the 1970s through the early 1990s were deathly quiet. Yet this same period, from about 1975 onward, coincided with the steepest rise in global temperatures -- a rise that is still continuing today.

Despite this rising warmth, only one major hurricane (Andrew in 1992) struck Florida between 1966 and 2003. This partly reflected a multi-decade shift in Atlantic currents and wind patterns, but also, the state was just lucky (although I'm sure those in Andrew's path didn't think so); the few storms that did form struck elsewhere or veered harmlessly out to sea. In the cooler period between 1926 and 1965, meanwhile, 14 major hurricanes made landfall in the Sunshine State. So on mathematical probability alone, you'd expect a good many more storms to be hitting Florida in the years ahead.

Commentators have also pointed to the enormous rise in property damage as proof that hurricanes are more severe. But the 25-year quiet period also coincided with massive development and population growth in U.S. coastal areas. Quite simply, everyone wanted to be near the beach. More people live in South Florida's Dade and Broward counties now than lived in the entire southeastern United States in 1930. As Florida International University tropical meteorologist Hugh Willoughby told me: "The hurricane damage statistics are driven entirely by economic factors -- there's just more stuff sitting around on the beach waiting to be blown or washed away."

But before you dismiss global warming as mere hype and rush out to buy another SUV, consider this: Climate models developed by tropical meteorologists predict significant changes in hurricane intensity as greenhouse gases accumulate in the atmosphere and add more heat to the oceans. According to Tom Knutson and Bob Tuleya, tropical climate modelers at the Princeton, N.J.-based Geophysical Fluid Dynamics Laboratory, we can expect a 20 percent increase in rainfall, and damage due to increased wind speeds might rise as much as 10 percent. That 10 or 20 percent may not sound like much, but add it to a top-ranked Category 5 monster headed for Mobile, Ala., and you've got a major disaster in the making. A bit like Ivan, in fact. Indeed, the authors conclude that "a greenhouse gas-induced warming may lead to a gradually increasing risk in the occurrence of highly-destructive Category 5 storms."

Already this year, as the NOAA graph suggests, the additional warming effect may be making itself felt. Although it's statistically impossible to isolate a tiny change among the sheer volatility of hurricane behavior, that all becomes rather academic to those in harm's way once the storms come onshore. After all, just a 2 percent increase in hurricane strength -- my rough guess for global warming's impact this year -- means that many more people in Port Charlotte, Fla., lost the roofs to their houses last month thanks to Hurricane Charley. An inch of extra storm surge might not sound like much, but that just might be the inch -- coming on top of a total 15 feet of higher water -- that overtopped coastal embankments and flooded large areas of vulnerable low-lying Gulf coastline during the passage of Hurricane Ivan. It would certainly have made a major difference to me driving along the North Carolina Outer Banks during the height of Tropical Storm (later Hurricane) Gustav two years ago. I remember streamers of sand blowing off the tops of the dunes and a combination of torrential rain and horizontal spray reducing visibility to almost zero at times.

We meddle with nature's fury at our peril, and strange things are happening to the world's weather these days. In March, the first-ever hurricane formed in the South Atlantic, striking Brazil with 90 mph winds and causing up to a dozen deaths. Meteorologists were left scratching their heads in bewilderment as the familiar swirl of clouds, complete with a well-defined eye, appeared in an oceanic basin where none had been spotted before. The Brazilian weather service, with no established naming sequence, had no idea what to call it, eventually settling on Catarina, after the state where it made landfall. Hurricane monitoring and warning services may now have to be extended 2,000 miles to the south of the equator to deal with the new threat. Scientists might have dismissed Hurricane Catarina as a sheer fluke, except that two other tropical storm-like formations also occurred in the same Southern Hemisphere summer.

The Pacific season has also been active: Japan has suffered its highest number of typhoon strikes on record, and the storms -- which hit at the rate of one a week for much of the summer -- wreaked havoc in Taiwan, China and the Korean Peninsula. While the link between these events and global warming is still disputable, clearer evidence of climate change is flooding in from around the planet. In my journey across the world investigating its impacts for my book, I climbed up to rapidly diminishing glaciers in the Peruvian Andes, suffered blinding dust storms in Inner Mongolia and waded through floodwaters in the drowning Pacific island archipelago of Tuvalu.

Whatever the scientific caveats about this Atlantic hurricane season, climate change remains a global reality -- and America is the only country in the world where the political debate has still not caught up with this fact. The current administration stands alone in its refusal to face up to the threat: Last week, George Bush's ally Tony Blair gave a major speech on the issue that brought the differences between the two governments into stark relief. The British prime minister said he considered climate change to be "a challenge so far-reaching in its impact and irreversible in its destructive power that it radically alters human existence," and pledged to make climate "a top priority" when Britain takes over the presidency of the G8 group of industrialized nations -- the United States, Britain, Canada, France, Germany, Italy, Japan and Russia -- in 2005.

To Blair and many others here in Europe, the Bush administration's laggard stance on global warming is a source of great frustration. Indeed, Blair began his speech by reminding the audience that "apart from a diminishing handful of skeptics, there is a virtual worldwide scientific consensus on the scope of the problem." As long as the U.S. government is counted among the ranks of these skeptics, the Europeans know that the chance of a meaningful global agreement is slim.

With only 4 percent of the Earth's population, the United States is responsible for a quarter of global greenhouse gas emissions. Hence the quiet hope expressed by many on this side of the Atlantic that Alex, Charley, Frances and Ivan -- and possibly Jeanne -- might help open Washington's eyes to the increasingly urgent need to confront climate change.

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Mark Lynas, a journalist specializing in climate change, is the author of "High Tide: The Truth About Our Climate Crisis" (Picador). He lives in Oxford, England.

Waves of wrath: Will powerful storms like Ivan destroy more property, like this condominium in Orange Beach, Ala.?