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."