75% Of Total Modern Glacier Melt Occurred Before 1950
“[T]he retreat of the glaciers after about 1925 became rapid. It was almost entirely during the [pre-1950] twentieth century warming that the Alpine glaciers disappeared from the valley floors up into the mountains. Similarly great retreats occurred in Scandinavia, Iceland, Greenland, in the Americas, and on high mountains near the equator.” — H.H. Lamb Climate, History, and the Modern World (1982), pg. 248
A new scientific paper indicates that the pronounced warming that occurred during the years stretching from the 1920s to the 1940s melted Northern Iceland glaciers much more extensively and at a far more rapid pace than has been observed in recent decades.
During the 1960s to 1980s, glacier melt rates not only decelerated relative to the 1920s to 1940s, the ice actually advanced in some cases due to decades of cooling. It has only been since about the mid-1990s that glaciers have consistently begun melting again — but with far less alacrity than they did in the first half of the 20th century.
Fernández-Fernández and co-authors (2017) indicate that the Icelandic glaciers they studied melted by more than 1,000 meters (1,062) on average between the late 1800s and 1946. But from 1947 to 2005, these same glaciers only retreated by an average of 272 meters more. In other words, about 75% of the total glacier melt production since the end of the Little Ice Age (the late 19th century) occurred prior to the mid-1940s.
Below are some key points and graphs from the paper.
“The abrupt climatic transition of the early 20th century and the 25-year warm period 1925–1950 triggered the main retreat and volume loss of these glaciers since the end of the ‘Little Ice Age’. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts. Stötter et al. (1999) indicate that the coldest period after the LIA was from the early 1960s to the mid-1970s, when temperatures fell to levels equivalent to the warmest recorded in the 19th century. This cooling is the reason given by Caseldine (1983, 1985a, 1985b, 1988) to explain the advance of the Gljúfurárjökull between the mid-1970s and the mid-1980s … Studies of aerial photographs and satellite images show that the glacier snouts have retreated by more than 1300 m on average since the LIA maximum (considered to be AD 1898 in Gljúfurárjökull and AD 1868 in both Western and Eastern Tungnahryggsjökull), with an altitudinal rise of more than 100 m. The retreat accelerated rapidly (15.3 m yr−1) during the first half of the 20th century. In the second half of the 20th century, the retreat decelerated considerably, reflected in the lowest values around 1985 (5.2 m yr−1) and a trend shift in 1994, with an advance observed in Gljúfurárjökull. … The retreat rate intensified in the period 2000–2005 compared with 1994–2000, but did not reach the rates recorded before 1946.”
Gljúfurárjökull, West Tungnahryggsjökull, and East Tungnahryggsjökull Glaciers:
1. During the period 1898–1946, the snout of Gljúfurárjökull retreated 635 m, almost two-thirds of the total distance from the LIA maximum (1898–1903) to 2005, at an average rate of 13.2 m yr−1.
2. The trend in Western Tungnahryggsjökull during the first half of the 20th century was a more rapid retreat, showing the highest average rates of the whole period (19.5 m yr−1). By 1946, this glacier had retreated almost 90% of the total recorded between the LIA maximum (1868) and 2005.
3. Just as in the glaciers described above, the retreat of the Eastern Tungnahryggsjökull from its LIA position was more intense during the first half of the 20th century, and in 1946 its snout was only 200 m from its current position. … The 2000 aerial photograph shows that an advance of at least 41 m had taken place since 1985. Nevertheless, between 2000 and 2005, the snout retreated 17 m, even more slowly than Western Tungnahryggsjökull.