It's hotter than you know what outside, and the sizzling temperatures are the surest sign yet that the theory of global warming is for real, right?

Well, no, not exactly, say climate scientists.

"We are definitely on the global warming train and it is headed for the horizon," said Bill Patzert, a climatologist at the Jet Propulsion Laboratory in Pasadena, in an interview Friday. "But this heat wave that we have been having for the last month or so, that is mostly meteorology."

Southern California has been locked in a huge stationary high-pressure system that has been baking the landscape and funneling moist air into the region from the Gulf of Mexico, climatologists say. A key factor in setting up the unrelenting system may be the persistent drought that residents of California and much of the Southwest have been enduring for the last seven years.

The recent temperatures, while on the extreme side, are not outside the natural variations of the region's climate, they say.

Besides that, one hot summer does not make a global warming trend any more than one cold winter makes another ice age, said Nigella Hillgarth, executive director for the Birch Aquarium at UC San Diego's Scripps Institution of Oceanography.

Edward Aguado, a climatologist in San Diego State University's Geography Department, put it this way: "It's irrational to say that this single scorching summer is proof that there is global warming. It's equally irrational to say that global warming is not real. Global warming is real, but it is not necessarily the reason why this summer has been particularly crummy."

But crummy it has been.

Heat records have been toppled everywhere. Temperatures have soared to 106 in Vista, 112 in Escondido, 113 in Lake Elsinore and 114 at the San Diego Wild Animal Park.

And because of the humidity, it hasn't been cooling off at night. Temecula, for example, set a mark for its warmest overnight low ever: 77 degrees.

"I really can't remember (a summer) this bad," said Aguado, who has lived in San Diego more than two decades. "It's very unromantic. The bedroom is very warm and muggy, and it just persists day after day."

Besides leaving people miserable, the heat wave's persistence has been frustrating.

"We just haven't had any relief from the Pacific, our great air conditioner," Patzert said.

But while scientists are as uncomfortable as anyone else, when it comes to assessing what it means they are less interested in this summer's record-smashing than in whether this type of heat will recur often in future summers.

"We do know that our planet has heated up one degree over the last 100 years, and most of that has happened over the last three decades or so," Hillgarth said. "If we continue to see a lot more of these hot summers, that will be a suggestion that something bigger is going on."

Many scientists believe the warming has been caused by widespread burning of fossil fuels, such as the gasoline that powers 20 million California cars and trucks. The burning has been pumping carbon dioxide into the atmosphere and creating a blanket that is increasingly trapping heat, they say. Some scientists, however, say they are skeptical about the climate change theory and that a direct connection between the one-degree global rise and fossil fuels has not been proven.

In Southern California, there has been an even greater rise in temperatures. Average daytime highs have risen three degrees over the last century, Patzert said, and nighttime lows have crept up seven degrees.

Fossil fuels have had something to do with that, he said. But a much more prominent factor has been the region's urban transformation. Patzert said that development has replaced large expanses of dry chaparral that used to give up heat readily at night with concrete jungles and moist lawns that retain warmth after dark -- and give the sun a running head start on the next day's high temperature.

"We've done an extreme makeover on the surface of Southern California," Patzert said.

With developers poised to blanket the region, and particularly fast-growing areas of North San Diego County and Southwest Riverside County, with even more housing tracts and shopping centers, it is a sure bet the air will get hotter still, Patzert said.

"The bottom line here is that the growth industry in Southern California is air conditioning," he said. "Send your children to air conditioning school."

And if climatologists are right about global warming, said Hillgarth, look out.

"We can expect to see more summers like this," she said.

- Contact staff writer Dave Downey at (760) 740-5442 or ddowney@nctimes.com.