Jahren briefly discusses the Earth’s water and ice. The majority of the Earth’s water belongs in the ocean; a much smaller portion of the planet’s water is fresh, and much of that is frozen as ice. We are losing much of our frozen, fresh water to warming temperatures. A majority of the world’s ice sits at the poles in the form of glaciers, sea ice, and massive ice sheets. Global warming is causing the polar ice caps to melt at an increasingly fast pace. As the ice melts, it floods the ocean and contributes to global sea level rise.

While the loss of glacial ice in regions like the Arctic and Antarctic is invisible to the average person, many have experienced the loss of their favorite wintertime recreation: Ice skating, skiing, snowshoeing, and ice fishing are all outdoor sports that are harder and harder to access. Ski resorts such as Aspen or Vail are forced to open later and later each winter, waiting for the snow that is increasingly slow to come.

In this chapter, Jahren explores how scientists are using instruments to study rising sea levels. Since 1880, the average global sea level has risen seven inches, in large part due to the melting polar ice caps that she references in the previous chapter.