With an average surface temperature of 15°C (and rising), much of our planet is inhospitable to ice. Today, less than 2% of Earth’s water exists in a frozen form, locked up in glaciers and ice sheets, sea ice and permafrost. This ‘cryosphere’ is critically important for controlling global sea level and the distribution of the planet’s fresh water, yet it has always existed in a rather perilous state. In contrast, the ice caps on Mars and the frozen surface of Jupiter’s moon, Europa, enjoy a much colder and more stable existence. To understand the impacts of climate change on Earth’s cryosphere, it is necessary to examine the different components of our icy world separately, for each has its own sensitivity to local and global forces.