This stunning Denver hotel says it’s ‘carbon positive.’ But what does that actually mean?

On a triangular lot in downtown Denver, a new boutique hotel boasts many of the amenities that make such a place a must-stay. Its slender frame and sleek rooms were designed by famed architect Jeanne Gang and Studio Gang, and it has a great location, a restaurant, and a stunning green rooftop, blooming with native flowers and plants, that showcases sunset views of the Rockies. But Populus, which opened earlier this month, wants guests to leave thinking about nothing but trees. Studio...