Climate change will have a "substantial" impact on human health in the coming decades, making wildfires and hurricanes more likely, cooking up more smog, and making summer heat waves longer, hotter and deadlier, according to a new report today from the Environmental Protection Agency.

    The report details how rising temperatures could slowly but significantly shift the rhythms of nature that Americans are used to -- with disruptive, sometimes even deadly, consequences. In the West, it found, changing weather patterns could thin the snowpacks that feed rivers, with repercussions for both hydroelectric dams and water supplies.

    And, in Washington and other Eastern cities, it found that a warmer climate will likely mean summers that start earlier, last longer and produce more periods of sustained heat.

    "It's going to be hotter, it's going to be hotter sooner in the year than it was in the past," said Kristie L. Ebi, an adjunct professor at George Washington University and one of the report's lead authors. She said that young people living in the D.C. area now will notice a difference before they reach middle age.

    "They're going to look back and think about how nice the summers used to be," Ebi said. "Within 20, 30 years, on average, the [public] should notice that it's warmer."

    The report was prepared under the EPA's leadership, but released by the U.S. Climate Change Science Program, which coordinates research among several federal agencies.

    Its conclusions are noteworthy in part because the Bush administration has resisted the conclusion that climate change will be definitively bad for human health. Last year, for instance, the White House refused to open an e-mail from the EPA forwarding a formal finding that climate change would endanger public welfare.

    Last week, the EPA officially requested public comment on the idea of regulating greenhouse gases -- the emissions blamed for climate change -- under the Clean Air Act. But, at the same time, the agency released documents disparaging that idea, saying that such a regulation would amount to unprecedented EPA interference into numerous sectors of the economy.