'EXTREME HEAT' DAYS BOILING OVER.

Byline: Robert Monroe Staff Writer

The number of ``extreme heat'' days per year has nearly doubled in Los Angeles and nationwide over the past half-century, according to a report released Wednesday by two environmental advocacy groups.

The report from Ozone Action and Physicians for Social Responsibility defines ``extreme heat'' days as those in Los Angeles that exceed an average of 74 degrees with humidity factored in.

In the 1950s, about 13 days a year rose above the threshold, as compared with 22 days in the 1990s, the report said.

The findings bolster what experts at the National Weather Service and elsewhere have reported: Temperatures have been increasing nationwide.

``It's costly, it kills and it's what scientists are telling us to expect a lot more of,'' said John Passacantando, executive director of Ozone Action.

The report's release was timed just a week before the Republican National Convention in an effort to make global climate change a top political priority.

It also comes as much of the nation is enduring a summer of record-breaking heat, and Los Angeles is experiencing triple-digit temperatures.

Temperatures on Wednesday reached as high as 96 in the San Fernando Valley and similar weather is expected today, National Weather Service officials said.

The report broke down heat data by major cities. It also found that the country and Los Angeles suffer through more heat waves annually now than before and that nights are significantly warmer than in the past.

The authors used a two-part measurement to reach their findings. They started with heat index measurements, the average temperature for all hours of the day all days of the year with humidity factored in.

The researchers took heat index data for all days between 1948 and 1999 and created a heat threshold, based on the temperature at which heat-related deaths begin to rise dramatically. All days that the temperature rose above a certain point were counted as ``heat stress days.''

William Brown, a meteorologist with the National Climatic Data Center, said the study matches his agency's conclusions about ever-increasing heat. His agency recorded winter 1999 and spring 2000 as the hottest winter and spring in 106 years of national record-keeping.

``Over the past 20 years, there is a definite rise in global as well as U.S. temperatures,'' he said.

Robert Musil, executive director of Physicians for Social Responsibility, said solutions for pollution and overpopulation must become part of the next president's policies.

``We would call on all top elected officials to make global warming a top issue on their platforms,'' he said.

Jet Propulsion Laboratory ocean scientist William Patzert noted National Weather Service data for Los Angeles as support for the group's finding. The temperature of the Los Angeles basin has risen five degrees on average between the 1880s and 1990s, according to its records.

``These people are absolutely correct,'' Patzert said.