Salt has been used to keep winter roads free of ice and snow since the 1940s. It works by lowering the freezing point of water. In the U.S. alone, some 15 million tons of salt is applied to roadways each year. While its use has real benefits, in terms of safety and navigation, there have been cumulative costs to the environment.
A central issue in dealing with climate change is determining how much carbon we can emit into the atmosphere before global temperatures increase too much. How much is too much? Most experts think that if average temperatures increase by more than 2 degrees Celsius (3.6 degrees Fahrenheit), the consequences will be severe and irreversible.