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WASHINGTON — The federal government’s sweeping new National Climate Assessment is more than just a dire warning about current and future global warming effects across the United States. It’s also the most detailed guide yet to all the ways the country will have to adapt.

Even if the nations of the world get their act together and slash fossil-fuel emissions rapidly, the United States will need to spend many billions of dollars to harden coastlines, rebuild sewer systems and overhaul farming practices to protect against floods, wildfires and heat waves that are already causing havoc nationwide. And the more that emissions rise, the more difficult and costly that task gets.

The United States isn’t prepared. In the Midwest, the report notes, only four counties and cities have written climate change plans. This in a region where scientists are forecasting bigger crop failures and heavier floods that could cripple transportation networks. And at the federal level, the Trump administration is rolling back policies to take future sea-level rise into account when building new roads and railways.