Global-mean sea-level rise (GMSLR) during the twentieth century was primarily caused by glacier and ice-sheet mass loss, thermal expansion of ocean water and changes in terrestrial water storage1. Whether based on observations2 or results of climate models3,4, however, the sum of estimates of each of these contributions tends to fall short of the observed GMSLR. Current estimates of the glacier contribution to GMSLR rely on the analysis of glacier inventory data, which are known to undersample the smallest glacier size classes5,6. Here we show that from 1901 to 2015, missing and disappeared glaciers produced a sea-level equivalent (SLE) of approximately 16.7 to 48.0 millimetres. Missing glaciers are those small glaciers that we expect to exist today, owing to regional analyses and theoretical scaling relationships, but that are not represented in the inventories. These glaciers contributed approximately 12.3 to 42.7 millimetres to the historical SLE. Additionally, disappeared glaciers (those that existed in 1901 but had melted away by 2015, and that therefore cannot be included in modern global glacier inventories) made an estimated contribution of between 4.4 and 5.3 millimetres. Failure to consider these uncharted glaciers may be an important cause of difficulties in closing the GMSLR budget during the twentieth century: their contribution is on average between 0.17 and 0.53 millimetres of SLE per year, compared to a budget discrepancy of about 0.5 millimetres of GMSLR per year between 1901 and 1990. Although the uncharted glaciers will have a minimal role in sea-level rise in the future, and are less important after 1990, these findings imply that undiscovered physical processes are not required to close the historical sea-level budget.
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The RGIv5 dataset used for glacier area distribution data are available from GLIMS at https://www.glims.org/RGI/randolph50.html with identifier doi:10.7265/N5-RGI-50. The updated glacier model output is available from the corresponding author upon reasonable request. The SGI is described in ref. 22 with identifier doi:10.1657/1938-4246-46.4.933, and data was available from the authors on reasonable request. The data generated for this paper is not provided owing to the difficulty of representing a collection of matrices indexed by glacier size class and year in a simple CSV file in a way that is easily readable, but the data is available from the corresponding author on reasonable request.
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This research is funded by the Austrian Science Fund (FWF) project P25362.
Nature thanks W. Pfeffer and the other anonymous reviewer(s) for their contribution to the peer review of this work.