The Randolph Glacier Inventory: a globally complete inventory of glaciers

TLDR

The Randolph Glacier Inventory is a globally complete digital outline collection of glaciers (excluding ice sheets) created to support IPCC mass‑balance estimates, but its errors are not normally distributed and quantifying them reliably remains unsolved. The RGI was assembled rapidly with limited resources, prioritizing coverage over detail, using 1999–2010 satellite imagery to outline ~198,000 glaciers and attaching a uniform attribute set, and its outlines are combined with digital elevation models to produce hypsometries for climate impact studies. The RGI estimates a total glacier extent of 726,800 ± 34,000 km² (≈ ±5 % uncertainty), mainly due to misinterpretation of seasonal snow and debris cover, and has already enabled significantly improved aggregate estimates of glacier mass change and volume, informing sea‑level rise assessments.

Abstract

Abstract The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the ~198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999–2010 provided most of the outlines. Their total extent is estimated as 726 800 ± 34 000 km 2 . The uncertainty, about ±5%, is derived from careful single-glacier and basin-scale uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise.