One of the world's most prominent hurricane researchers, the Massachusetts Institute of Technology's Kerry Emanuel, has proposed a stunning theory that suggests the AMO has a minor effect on hurricanes - and may not even exist at all.

"I'm worried about what the data is telling us," Emanuel said. "It's a pessimistic message, but barring a major (El Niño event), and barring a big volcanic eruption, there just isn't an objective basis for expecting a downturn in Atlantic hurricane activity."

During large El Niño events, when the Pacific Ocean warms, hurricane activity in the Atlantic generally diminishes. Volcanoes spew ash that reduces sunlight, lowering temperatures and likely also diminishing hurricane activity.

The recent upswing in storms is largely because of human-induced climate change, Emanuel contends. The unrelated, noncyclical events that reduce hurricane activity, including volcanic eruptions, have masked a progressive rise in sea temperatures because of global warming, he said.

Emanuel and a handful of other scientists previously have courted controversy with articles suggesting that climate change already is making hurricanes more forceful, with measurably stronger winds.

Global warming debate

This earlier work, especially after the 2004 and 2005 hurricane seasons, has ignited a scientific debate about the effect of a warming world on hurricane activity. If there's a general consensus, however, it's that climate change is likely to have some yet unknown effect on tropical storms, and that such an effect would be too small to measure yet.

A majority of scientists think if climate change is affecting hurricanes around the globe, its effect on the North Atlantic basin is minor compared with the influence of the AMO. Indeed, near the end of the record 2005 season, the National Oceanic and Atmospheric Administration released this statement:

"NOAA research shows that the tropical multi-decadal signal is causing the increased Atlantic hurricane activity since 1995, and is not related to greenhouse warming."

Emanuel first presented his new theory late last month at a hurricanes and climate change conference at Columbia University.

Among those in attendance was Phil Klotzbach, a hurricane researcher at Colorado State University who now does much of the research for Bill Gray's seasonal hurricane predictions, the oldest and best-known annual forecast. Klotzbach said he remains unconvinced.

"Dr. Gray and I believe that the AMO plays a large role in North Atlantic sea surface temperatures," he said.

Klotzbach said the data indicates a large increase in tropical Atlantic sea surface temperatures in 1994 and 1995. This sudden spike, he said, does not fit well with a greenhouse warming theory that would likely exhibit a smoother trend.



Other climate scientists who viewed Emanuel's talk admitted, however, that uncertainty exists within the AMO theory. Most agree it's difficult to determine exactly what is driving late summer temperatures in the tropical Atlantic - be it natural climate variability, greenhouse gases or some other factor, such as volcanic eruptions.

Arriving at solid answers is difficult because of limited data. Although reliable sea surface temperature records exist back to the mid-1850s, hurricane records are less reliable. It is difficult for scientists to compare modern accounts of storm frequency and, more importantly, wind speeds with historical records because of vastly more measurements today from satellites, airplanes and sophisticated equipment in the seas.

A modern hurricane's windspeed is measured dozens if not hundreds of times before landfall. The great Galveston storm of 1900 has just one such measurement.

The AMO theory holds that an active period ended in 1900, followed by relative calm until 1930, high activity until about 1970, and calm again until the recent period of higher-than-normal storm activity began in 1995. The oscillation closely tracks the ups and downs in Atlantic sea temperatures.

About a decade ago, a hurricane researcher named Chris Landsea re-examined wind and pressure data for hurricanes from the last active period, between the 1930s and 1960s. He found that the intensity of storms from the era may have been slightly overestimated, and suggested a "bias correction."

Looking for an explanation

Emanuel has seized upon Landsea's correction and inserted it into his measure of a storm's intensity called the "power dissipation index," which estimates the overall destructive potential of a storm.

Emanuel's calculations show a rise in activity to about 1950, followed by a decline to about 1980, then a rapid increase. This does not conform to any AMO, he says. Rather, it follows the entire northern hemispheric temperature record, which shows a similar pattern.

The cooling between 1950 and 1980, he and some other climate scientists say, is a consequence of sulfate aerosols, which blacken the atmosphere and block some sun rays from reaching the Earth's surface.

Landsea, now a meteorologist at the National Hurricane Center, and Emanuel have sparred about whether the bias correction should be employed in current theories without verification.

Although he says the AMO doesn't explain all of the cyclical nature of hurricanes in the Atlantic, Landsea still thinks the Americas will continue to experience active and inactive periods of storminess.

"I thought his analysis was interesting, but I think it's far from definitive," Landsea said of Emanuel's presentation.

Landsea is leading a collaborative work among hurricane scientists to reanalyze the storm record and try to reach consensus about the data.

For example, the study led to raising 1992's Hurricane Andrew to Category 5 status a decade after it struck land. With better data, Landsea said, perhaps scientists can achieve a final answer on the role of the AMO and hurricanes.

One problem with the AMO idea is that despite the apparent relationship between oscillating sea temperatures, atmospheric changes and hurricane activity, scientists have yet to find an explanation in nature for why such a cycle would exist. There's some thought that it may be because of large-scale circulations of water deep in the oceans, but no one's sure.

For this reason, Florida State University hurricane specialist James Elsner said he finds Emanuel's theory plausible.

But for now, most leading hurricane scientists will continue to adhere to the idea that at some point, storm activity will quiet down again.

But when the laughing stopped, an expert theorized it probably fell from the wheel well of a plane landing at Oakland or San Francisco International airports. It also could be an unexplained "ice fall," one expert said. Big balls of ice sometimes fall from the sky without any real explanation.

Wherever it came from, it's arrival was heart-stopping and dramatic.

Brooks and Judith Mencher said they were standing on their back porch on 59th Street near the park when they heard a sound like a very loud rocket. "It kind of went 'whoosh!'" Brooks Mencher said.

The impact hole looked like it was created by a hand grenade, said Oakland Police Sgt. Ron Lighten. "It knocked turf 20 feet away."

Lt. Charles Glass of the Oakland Fire Hazardous Materials Team said the ice was pure water. " It didn't come from a toilet on a plane or anything like that."

Glass said the ice that firefighters pulled from the hole was about the size of the hole, three by three feet and two and a half feet deep. It also broke a ceramic irrigation pipe at the bottom of the hole.

At Oakland International, a spokeswoman said she had no idea if a plane might have been going overhead at that moment. "We'll have to wait until Monday, when that information is available," she said.

Web sites that track commercial flights show a spike in arrivals at Oakland International at about the time, 10:05 a.m., that the ice ball put a hole in Bushrod Park. Two runway approaches for San Francisco International also go almost directly overhead.

An operations manager at the Federal Aviation Administration in Los Angeles said he had never heard of such a thing.

"I've been here 15 years and what usually falls from planes is 'blue ice,' that's methylene glycol. They put it in airplane toilets. Sometimes there are leaks and it falls out," he said.

But Tony Hirsch, a Columbus, Ohio-based aviation expert, said ice falls of pure water are not uncommon: "Ice builds up on airplanes and falls off as they prepare to land."

But Hirsch said the airplane "would have to descend through what we call visible moisture, rain or clouds, for ice to build up." The skies were partly cloudy Saturday morning.

Hirsch said a large chunk of ice could build up on the vertical stabilizer or in a wheel well: "When they lower their landing gear, it falls off."

As bad as Bay Area weather has been, the National Weather Service said none of the storms has been violent enough to hatch a gigantic hailstone on its own. "There's nothing meteorological that would create a piece that big falling into Oakland," said weather service forecaster Diana Henderson.

Electrical engineer Richard Spalding thinks there must be another explanation. He tracks meteors as part of work on satellite instruments and became interested in balls of ice that smash down from time to time.

"Ice falls do happen fairly frequently," Spalding said. "Just about every year, there's a news item somewhere. I think it came from a natural process that we're ignorant of, where it can form at altitude and fall as a chunk," he said.

There's at least one recorded incident of ice from a plane hitting a house. It happened in 2004 in Kent, near Seattle. Homeowner Troy Halte said Saturday a chunk of ice made a basketball size hole in his roof and the ice landed in softball-size pieces on this daughter's bed.

"Fortunately, nobody was home," he said.

The broadcaster said there is no danger of tsunami, powerful ocean waves caused by seismic activity.

Japan, one of the world's most earthquake-prone countries, is located in a zone where the Eurasian, Pacific, Philippine and North American tectonic plates meet and occasionally shift, causing quakes. Quakes of magnitude 5 and more can cause considerable damage.

In India, as many as 160 people were injured when three large cloth tents collapsed in flames on top of those gathered inside to view new stereos, TV sets, washing machines and other appliances.

The trade show was being held in Meerut, a city located in the state of Uttar Pradesh about 80 kilometres northeast of New Delhi.

"Dead bodies are strewn around, most of them are charred beyond recognition," witness Prakash Arya told the Associated Press.

"The bodies were dumped into trucks, jeeps and ambulances and taken away from the public glare."

Witnesses blamed a short circuit that ignited plastic sheeting hung over an air conditioner. They also said many people died because the first tent to catch fire had only one exit.

The late-afternoon blaze at a park in the centre of Meerut was extinguished quickly, authorities said.

Meanwhile, in China an explosion rocked a hospital parking garage, killing at least 27 people.

But the death toll could rise as rescuers remove the rubble of an underground garage, the official Xinhua news agency said .

The employer, Xuangang Coal and Electricity Co. Ltd. in Shanxi province, had "no idea how many people were missing" or what caused the explosion, the news agency said.

Most of the victims were hospital staff and their family members.

Further to the west, in Gansu province, a truck crashed into a minivan and a passenger bus after its brakes failed, killing at least 26 people and injuring 24, Xinhua said. Seven people were killed on the spot and 19 died later.

An additional six people, including a three-year-old child, were seriously injured.

Personalities including Hillary Clinton have attended a memorial service for Dana Reeve, actress and widow of Superman actor Christopher Reeve.

Actor Philip Seymour Hoffman was among those at the New York service.

New York senator Mrs Clinton said Reeve was "one of the most exceptional people I have ever known".

Reeve, 44, cared for her husband after he was paralysed in an accident, and led his charity fund. She died of lung cancer in March.

Speaking after the service, Mrs Clinton - wife of former President Bill Clinton - said it had been "a very fitting tribute".

"She had a light within her that was captured by the way people talked about her today, especially her son and stepchildren," she said.

The Producers actor Matthew Broderick said the two-hour private service had been "beautiful but very, very sad".

CNN news presenter Paula Zahn, a long-time friend, said she had not resorted to self-pity after being diagnosed with cancer and "had a positive impact on everyone and everything she touched".

"She really expected to come home," said Zahn. "She truly believed she had more time."

Other celebrities attending included actor and comedian Robin Williams, cyclist Lance Armstrong and US TV presenter Barbara Walters.

Reeve, a non-smoker all her life, was a singer when she met her husband.