Abstract
The volume of glaciers in Iceland (∼3,400 km3in 2019) corresponds to about 9 mm of potential global sea level rise. In this study, observations from 98.7% of glacier covered areas in Iceland (in 2019) are used to construct a record of mass change of Icelandic glaciers since the end of the 19th century i.e. the end of the Little Ice Age (LIA) in Iceland. Glaciological (in situ) mass-balance measurements have been conducted on Vatnajökull, Langjökull, and Hofsjökull since the glaciological years 1991/92, 1996/97, and 1987/88, respectively. Geodetic mass balance for multiple glaciers and many periods has been estimated from reconstructed surface maps, published maps, aerial photographs, declassified spy satellite images, modern satellite stereo imagery, and airborne lidar. To estimate the maximum glacier volume at the end of the LIA, a volume–area scaling method is used based on the observed area and volume from the three largest ice caps (over 90% of total ice mass) at 5–7 different times each, in total 19 points. The combined record shows a total mass change of −540 ± 130 Gt (−4.2 ± 1.0 Gt a−1on average) during the study period (1890/91 to 2018/19). This mass loss corresponds to 1.50 ± 0.36 mm sea level equivalent or 16 ± 4% of mass stored in Icelandic glaciers around 1890. Almost half of the total mass change occurred in 1994/95 to 2018/19, or −240 ± 20 Gt (−9.6 ± 0.8 Gt a−1on average), with most rapid loss in 1994/95 to 2009/10 (mass change rate −11.6 ± 0.8 Gt a−1). During the relatively warm period 1930/31–1949/50, mass loss rates were probably close to those observed since 1994, and in the colder period 1980/81–1993/94, the glaciers gained mass at a rate of 1.5 ± 1.0 Gt a−1. For other periods of this study, the glaciers were either close to equilibrium or experienced mild loss rates. For the periods of AR6 IPCC, the mass change rates are −3.1 ± 1.1 Gt a−1for 1900/01–1989/90, −4.3 ± 1.0 Gt a−1for 1970/71–2017/18, −8.3 ± 0.8 Gt a−1for 1992/93–2017/18, and −7.6 ± 0.8 Gt a−1for 2005/06–2017/18.
Highlights
Glaciers in most areas of the world are losing mass as global temperatures rise in response to increased greenhouse gas concentrations in the atmosphere (e.g., Vaughan et al, 2013; Hock et al, 2019; Meredith et al, 2019; Zemp et al, 2019)
The glacier areas are derived from Hannesdóttir et al (2020); we describe the method below and the resulting mass change rates calculated from the area and volume changes are shown with purple boxes in Figures 3A,B,C. (7) To include an estimate of mass change for other glaciers than Vatnajökull, Langjökull, and Hofsjökull in the periods 1890/ 91–1944/45 and 2017/18–2018/19, the net mass change of those three is multiplied by F 1.130, which is the ratio between mass change of all glaciers in Iceland in 1945/ 46–2016/17 and the mass change of the three large ice caps in the same period
The results presented here add valuable information to global estimates of the response of glaciers to climate change in the past several decades
Summary
Glaciers in most areas of the world are losing mass as global temperatures rise in response to increased greenhouse gas concentrations in the atmosphere (e.g., Vaughan et al, 2013; Hock et al, 2019; Meredith et al, 2019; Zemp et al, 2019). In situ mass-balance observations are sparse (e.g., Zemp et al, 2020a), but with the aid of satellite and other remote-sensing data, an increasingly clear picture of glacier mass loss around the world has been appearing (e.g., Brun et al, 2017; Wouters et al, 2019; Morris et al, 2020; Shean et al, 2020). Glacier mass loss is a global phenomenon, and the rates in the early 21st century are unprecedented for the observed period (Zemp et al, 2015). Reconstructions of glacier mass-change rates for the 20th century and the first decade of the 21st century show substantial temporal and spatial variations, but a global mass loss trend became clear toward the end of the 20th century (Leclercq et al, 2011; Marzeion et al, 2015; Marzeion et al, 2012). Glaciers in Iceland are all temperate and cover about 10% of the area of the country (Björnsson and Pálsson, 2008), with the largest ice cap Vatnajökull (∼7,700 km2, ∼2,870 km, in the year 2019) located near the southeast coast, two smaller ice caps Langjökull (∼835 km2, ∼171 km, in the year 2019) and Hofsjökull (∼810 km2, ∼170 km, in the year 2019) in the central highlands [area estimates are from Hannesdóttir et al (2020) and volumes are calculated in this study], and Mýrdalsjökull [∼598 km2, ∼140 km, in the year 1991
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