Figure 3.1

The Great Lakes. In 2013, Lakes Huron and Michigan dropped by 1 m (3.3 ft), reaching their lowest level in recorded history. Large cargo vessels (inset) must take on less cargo to float higher in the water to pass through the shallow channels connecting the lakes. If less cargo is moved, costs to transport cargo increase.

(Map, NASA; photo, Peter Hawkins/DanitaDelimont.com”Danita Delimont Photography”/Newscom)