Apart from Antarctica, Patagonia is home to the biggest glaciers in the southern hemisphere, but some are retreating faster than anywhere else in the world. This is because the weather is relatively warm and these glaciers typically terminate in fjords and lakes, exacerbating surface melting and causing them to flow faster and lose ice as icebergs at their margins. Traditionally, it has been very difficult to map exactly how fast these glaciers are changing. However, a new way of processing ESA CryoSat swath data now makes it possible to map these glaciers in fine detail. CryoSat has revealed that between 2011 and 2017, there was widespread thinning, particularly in Patagonia’s more northern ice fields. The Jorge Montt glacier, which flows down to the ocean, retreated 2.5 km and lost about 2.2 Gt a year. In contrast, Pio XI, the largest glacier in South America, advanced and gained mass at a rate of about 0.67 Gt a year. However, over the six-year period, the glaciers overall lost mass at a rate of over 21 Gt a year. This loss is adding about 0.06 mm a year to sea level.