Global warming is causing more frequent hurricanes in the North Atlantic and Gulf of Mexico, according to a study from the National Center for Atmospheric Research.

The increased frequency of tropical cyclones “is largely a response” to a 1 degree Celsius rise in sea water temperatures since 1905 that was caused by greenhouse gases, the study found. Since 1995, the North Atlantic has experienced an average of 15 tropical storms a year, of which eight became strong enough to be called hurricanes. That compares with 10 tropical storms and five hurricanes a year from 1930 to 1994, the report says.

“There is an 80% chance that the majority of the current increases have been impacted by global warming,” said Greg Holland, director of the research center in Boulder, Colo., and co-author of the study. “The bad news is that we’ve gone up in numbers overall, and in the proportion of major hurricanes as well.”

The study by Mr. Holland and Peter Webster of the Georgia Institute of Technology adds weight to a U.N. panel’s conclusion this year that climate change is likely caused by humans and will increase floods and droughts, change growing seasons, and harm wildlife.

Hurricanes are so-called tropical cyclones, characterized by a circular wind pattern fed by warm ocean waters. Tropical storms become hurricanes when their winds reach 74 miles an hour and are categorized as major hurricanes at 111 mph. Mr. Holland said the increased hurricanes since 1995 may be a transition to a period in which the number of killer storms could be higher than at any time in the past.

William Gray, head of the Tropical Meteorological Project at Colorado State University, said an increase in sea temperatures that is creating more hurricanes in the North Atlantic is the result of natural processes, not global warming induced by human activity. The current cycle of warmer water temperatures and more hurricanes should end in 10 or 20 years, he said.

Holland “misrepresented the data,” Mr. Gray said in an interview yesterday. “We’re coming out of a little ice age and yes, the Atlantic has gotten a little warmer in the last 100 years, but this is due to natural processes,” Mr. Gray said. “It’s a terrible paper.” Chris Landsea, science and operations officer at the National Hurricane Center, said Messrs. Holland and Webster erred by not accounting for storms that were missed before the introduction of satellite tracking in 1965 and other technologies.

“At a minimum, we missed three to four storms a year from 1900 to 1965,” Mr. Landsea said in an interview. Global warming “is not having an affect,” on hurricane frequency, he said.

Growing concern about climate change has prompted at least five attempts in Congress to set limits on U.S. emissions of carbon dioxide and other gases that can heat the atmosphere. The record 2005 hurricane season and the flooding of New Orleans after Hurricane Katrina helped change U.S. public opinion about global warming.

Hurricanes in 2005 killed more than 1,300 people, destroyed towns along the Gulf Coast, left New Orleans submerged and depopulated, and disrupted oil and natural gas production.

“There’s nothing that focused the public mind on global warming more than Hurricane Katrina,” David Doniger, climate policy director for the Washington-based Natural Resources Defense Council, said in an interview.

Senator Bingaman, a Democrat of New Mexico, and Senator Specter, a Republican of Pennsylvania, proposed a bill to cut U.S. greenhouse gases 20% by 2030. President Bush has rejected mandatory limits on greenhouse gases arguing they would hurt the U.S. economy. Energy Secretary Samuel Bodman followed the U.N. report by saying that the human causes of climate change are no longer up for debate.

Mr. Holland said a 2005 report from the National Oceanic and Atmospheric Administration that denied links between increased hurricanes and greenhouse gases was “unfortunate.” Released after Hurricanes Katrina and Rita, the study failed to reference peer-reviewed scientific literature contrary to its conclusion, Messrs. Holland and Webster write in their study.

The report from NOAA, which is part of the U.S. Commerce Department and the parent agency of the National Hurricane Center, “was neither necessary nor was it good advice to the American public,” Mr. Holland said in the interview.

Because the increases in hurricane frequency occur in steps, they cannot be attributed to changes in the way data on storms is collected, Mr. Holland said.

“Collectively, this causal chain leads to the strong conclusion that the current level of tropical cyclone activity in the North Atlantic is largely a response to climate change from anthropogenic causes,” says the report, to be published by the Royal Society in London.