Attribution of global glacier mass loss to anthropogenic and natural causes

Putting the heat on Mother Nature Humans are now the biggest cause of glacier melting. Until recently, that was not true. Glaciers take a long time—decades to centuries—to respond to the environmental changes that control their sizes. They have been retreating gradually from the peak levels they reached in the middle of the 19th century, at the end of a 500-year-long cold period called the Little Ice Age. Marzeion et al. show that that has recently changed though, as climate warming has continued: Over the past 20 or so years, the anthropogenic contribution to glacial mass loss has increased markedly (see the Perspective by Marshall). Science , this issue p. 919 ; see also p. 872