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Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes in glacier melt independently from model output. Here, we present a comprehensive database of Greenland glacier surface mass-balance observations from the ablation area of the ice sheet and local glaciers. The database spans the 123 a from 1892 to 2015, contains a total of ~3000 measurements from 46 sites, and is openly accessible through the PROMICE web portal (http://www.promice.dk). For each measurement we provideX, YandZcoordinates, starting and ending dates as well as quality flags. We give sources for each entry and for all metadata. Two thirds of the data were collected from grey literature and unpublished archive documents. Roughly 60% of the measurements were performed by the Geological Survey of Denmark and Greenland (GEUS, previously GGU). The data cover all regions of Greenland except for the southernmost part of the east coast, but also emphasize the importance of long-term time series of which there are only two exceeding 20 a. We use the data to analyse uncertainties in point measurements of surface mass balance, as well as to estimate surface mass-balance profiles for most regions of Greenland.

This glossary, produced by a Working Group of the International Association of Cryospheric Sciences (IACS), is the first comprehensive update of glaciermass-balance terms for more than 40 years. The mass balance of a glacier is a measure of the change in mass of the glacier, or part of it, over a period of time. Mass-balance data help to explain why a particular glacier system may be advancing or retreating and what climate drivers (e.g. decreased snow accumulation; increased surface melt) are responsible for the changes. Fluctuations of the si ze (most typically length, but also area and/or surface elevation) are observed for several thousand of the well over 100,000 glaciers distributedglobally from equatorial mountains to polar ice sheets. However regular annual mass-balance measurements are made on fewer than 200 glaciers. Mass-balance information is essential for defining the links between past, present and future climate ch anges and changes to glaciers in assessments such as those made by the Intergovernmental Panelon Climate Change (IPCC). Having a systematic, concise and unambiguous mass-balance terminology is a critical part of this.The first systematic attempts to define mass-balance terminology (UNESCO/IASH, 1970; Anonymous, 1969) were made during the United Nations Educational, Scientific and Cultural Organization (UNESCO) International Hydrologic al Decade (IHD, 1965-1974). The IHD programmeprovided an important impetus to international collaboration in hydrology and, in 1975, was succeeded by the UNESCO International Hydrological Programme (IHP). IHP has an emphasis onmethodologies for hydrological studies, training and education in the water sciences and on the adaptation of the hydrological sciences to cope with the expected changing climate and environmental conditions. It is hence fitting that this glossary is published as part of the IHP series ofTechnical Documents in Hydrology.This publication is also a crucial early milestone in the work of the International Association of Cryospheric Sciences. IACS is the eighth and newest Association of the International Union ofGeodesy and Geophysics (IUGG). Although it has prece dents reaching back to the 1894 International Commission on Glaciers, IACS only became a full IUGG Association in 2007. This volume is the first work conceived and completed during t he period that IACS has been a full Association. IACS isgrateful to the International Hy drological Programme of UNESCOfor providing the opportunity to publish the glossary as the second volume in a joint series.The mass-balance definitions and terminologiesdocumented during the IHD have served well formore than 40 years. There are however some ambiguities in current usage, and new technologies (e.g.space-borne altimeters and gravimeters, ground penetrating radars, etc.) are now used for mass-balance measurements, particularly of ice sheets. This new glossary addresses these, promotes clarity,and provides a range of useful ancillary material.IACS, and the glaciological communityas a whole, is very gratefulto the Chair of the WorkingGroup, Graham Cogley, and his dedicatedteam of volunteers for producing this volume. It is intendedthat the Working Group will continue to serve and to produce further reference publications on topicssuch as mass-balance measurement techniques and guidelines for reporting measurement uncertainty.Ian AllisonPresident, International Association of Cryospheric SciencesHobart, AustraliaJanuary 2011

Why Do We Expect Glacier Melting to Increase Under Global Warming?