Recently, I came across one of those fascinating side-by-side photographic comparisons, one showing a scene as it appeared in the 19th century and the other, taken from the exact same spot, showing how it looks today. The two photographs were of Yosemite Valley, the early one taken in 1866 and the other in 2009. The striking difference between them was that trees were much more abundant in the later shot. Most Americans would probably assume the reverse to be the case.