Though progressive politics at the turn of the 20th century called for the protection of America’s national parks, it did so for the enjoyment of white people.

It's hard to preserve national parks "unimpaired," as US law directs, when they're overrun with tourists who stray off paths, strew trash and harass wildlife. A parks scholar calls for crowd control.

With growing drought, rising seas and heavier storms, how do we protect Venice and other world treasures? The answer: creative, proactive measures that may alter them in important ways.