Scientists have fretted about glacier melt for years, and over the West Antarctic Ice Sheet in particular since the 1970s. The Thwaites Glacier, the sheet’s “weak underbelly”, saw its grounding-line retreat 14 kilometres (8.7 miles) between 1992 and 2011, for example, and some fear nothing can be done to save it from collapse—irretrievable loss. Deep valleys in Greenland’s ice sheet may mean it melts much faster than once expected, hastening sea-level rise and disrupting ocean-circulation patterns. And shrinking glaciers in mountainous parts of the world, such as California and northern India, mean farmers lack meltwater for their crops. Studying observations over four decades, the IPCC is confident that glaciers, alongside the thermal expansion of warmer water in the ocean, explain 75% of the rise in sea level in the past century.
