CHICAGO — The Windy City is preparing for a heat wave — a permanent one.

Climate scientists have told city planners that based on current trends, Chicago will feel more like Baton Rouge than a Northern metropolis before the end of this century.

So, Chicago is getting ready for a wetter, steamier future. Public alleyways are being repaved with materials that are permeable to water. The white oak, the state tree of Illinois, has been banned from city planting lists, and swamp oaks and sweet gum trees from the South have been given new priority. Thermal radar is being used to map the city’s hottest spots, which are then targets for pavement removal and the addition of vegetation to roofs. And air-conditioners are being considered for all 750 public schools, which until now have been heated but rarely cooled.

“Cities adapt or they go away,” said Aaron N. Durnbaugh, deputy commissioner of Chicago’s Department of Environment. “Climate change is happening in both real and dramatic ways, but also in slow, pervasive ways. We can handle it, but we do need to acknowledge it. We are on a 50-year cycle, but we need to get going.”

Across America and in Congress, the very existence of climate change continues to be challenged — especially by conservatives. The skeptics are supported by constituents wary of science and concerned about the economic impacts of stronger regulation. Yet even as the debate rages on, city and state planners are beginning to prepare.