It has been in the news of late that the North Pole ice cap has shrunk to the smallest size ever recorded. The previous minimum was in 2007.
Climate change denialists maintain that it is just normal variation and if you look at maps of the North Pole from the 1920s, 30s and 40s, the size of ice cap was similarly small. Indeed, the extent of the ice cap did hit a minimum in 1938 based on those maps.
Thankfully the Artic Sea Ice Blog went over those maps and the latest satellite images and pointed out that the extent of the ice cap now is still much smaller than it was in the old maps. But the comments were even better since one of the commentators pointed to this map that overlays the satellite data on the 1938 map:
One needs to be careful when comparing the current maps, which are more accurate in both space and time, with the older maps which the reflect the more limited ability people had to observe the North Pole ice cap.
Even still, it makes the point quite vividly, doesn't it?