Meteorologists who keep records for the National Oceanographic and Atmospheric Administration say that the United States is having its deadliest tornado season in a decade and that this year may be on pace to set a record for the most tornadoes.

At least one Arkansas family already knows that 2008 has been a devastating year for tornadoes.

John Hill, 31, lost his job on Feb. 2 when a huge twister demolished the boat factory in Clinton where he worked as a welder. Little more than three months later, Hill, who was struggling to provide for his family, lost his house, cars and cash savings to another tornado.

"I don't know what this is," said Hill, whose family survived the second tornado with bruises and gashes. "I've lived in Arkansas most of my life and I've never seen this many tornadoes. They're all over the place."

Meteorologists who keep records for the National Oceanographic and Atmospheric Administration say that the United States is having its deadliest tornado season in a decade and that this year may be on pace to set a record for the most tornadoes.

At least 100 people have been killed through mid-May, the highest number of fatalities since the same period in 1998. A preliminary tally shows 868 tornadoes were reported through May 18, a pace on par with 2004, which saw an unprecedented 1,819 tornadoes, according to records kept by the National Weather Service Storm Prediction Center in Norman, Oklahoma.

"It will be one of the biggest years, when all is said and done," said Harold Brooks, a research meteorologist at the center.

The numbers have the attention of Richard Heim, a meteorologist at the federal government's National Climatic Data Center who is responsible for keeping weather records and putting them in context. "It's been very, very active and very unusual," Heim said.

This tornado season has been atypical because of its early start. From 1953 to 2005, an average of 19 tornadoes struck in January and 21 in February, Heim said. In 2008, 136 tornadoes were reported in January and 232 in February.

The South, outside the storm belt where scientists expect to see tornadoes, has been especially hard hit. According to the Storm Prediction Center, Missouri and Mississippi have each had more than 100 twisters this year. Alabama, Arkansas and Georgia have seen more than 80 each.

The increase, the unusual timing and the geographic distribution are tougher questions to tackle, experts said.

The season probably got started earlier this year, Heim said, because of La Niña, a weather phenomenon that causes warmer winter temperatures in the Southeast. It also is likely that more tornadoes have been reported because meteorologists have gotten better at detecting them. But several groups of researchers have started to ask if the country is seeing more severe weather because of climate change.

"Our work suggests that the trend, the sign, is that conditions for severe weather will increase," said Robert Trapp, an associate professor of atmospheric science at Purdue University.

Trapp found that if human contributions to greenhouse gas emissions raised the global mean temperature by two to six degrees Celsius by the end of the century, the number of days with conditions that could create severe thunderstorms could double in cities in the South and along the Eastern Seaboard, including New York. His study was published in December in the Proceedings of the National Academy of Sciences.

Trapp warned that having the right conditions did not necessarily mean a thunderstorm or a tornado would form, and that his models could not predict when they would occur. So for now, Trapp and other experts agree, there is not enough good data to say if climate change is causing more tornadoes.

But in Arkansas, Hill's wife, Jackie, said she needed no more evidence about the cause of the twisters.

"I think people are just using too much of the resources," she said. "They're just messing with the ecosystem too much."