Hot enough for ya’ outside? Much of the United States is enduring another week of temperatures near or above 90 after a series of deadly July heat waves around the world. Get used to it, say weather experts. Global warming, which virtually all scientists now agree is a long-term trend caused by air pollution, is “very strongly” linked to abnormally hot stretches, explains the chief climate analyst at the National Center for Atmospheric Research. “There are very good reasons to believe that the current U.S. heat wave is at least partly caused by global warming," adds that specialist, Kevin Trenberth.

Although summer traditionally brings scorching days or weeks in some areas, scientists say those conditions become more intense and longer-lasting because global warming creates drier days and warmer nights all year. "You cannot attribute a single heat wave to global warming," says Inez Fung, director of atmospheric sciences at the University of California-Berkeley. "But in the future there will be more of these heat waves because of global warming."

The first six months of 2006 were the warmest in the United States since record-keeping began in 1895, according to the National Climatic Data Center. The 10 hottest years on record have all occurred since 1990, a trend that a majority of scientists say stems largely from the "greenhouse effect" caused by emissions from factories and vehicles that trap heat in the atmosphere. Computer projections show temperature peaks will continue on an upward arc in coming decades -- a dangerous trend discussed by former Vice President Al Gore in a documentary film, An Inconvenient Truth, now in theaters.

Expert says: "What we now call extreme events are becoming run-of-the-mill happenings. There is nothing we can do to stop it now. The only question is how big a hit we are going to take." -- Tim Barnett, climatologist at the Scripps Institution of Oceanography in Los Angeles, where it hit 110 degrees last week.

Skeptic says: “I don’t think there is any climatologist or meteorologist that would say you could draw a conclusion about any given year. There have been hotter periods in the past and we will have them in the future. If this persisted for a very long time, then you might be able to conclude that human activities had an impact.” -- Bill O’Keefe, oil industry consultant in Washington, D.C.

What’s ahead? August will be hotter than usual in many parts of the United States, forecasters say. And computer "climate models all agree on the intensification of heat waves in the future," warns Claudia Tebaldi at the National Center for Atmospheric Research in Boulder, Colo.