Why are the glaciers melting?

Glaciers survive, thrive, melt, fragment and disappear, all as result of its mass balance (read about glacier mass balance here). Like many things on Earth, the life of a glacier is in fine balance with the local climate. 1) Winter prevails, temperatures are cold and snow falls, some of it forming into glacier ice. 2) Summer arrives, temperatures rise and snow and glacier ice melts away. Repeat. Nearly every glacier on earth melts, it’s part of the cycle of water and balance of the world. Things begin to change when we get a bit too much of 2) and not enough 1).

Enter climate change. Air temperature averaged across the globe shows clear evidence of anomalous warming in recent decades compared to a reference period of 1981-2010 (Figure 1).  This warming is not consistent and exactly the same across the whole world and shows a lot of regional variation (Figure 2). Nevertheless, the general consensus of the Intergovernmental Panel on Climate Change (IPCC) ¹ is that our planet is warming, and in large part, due to greenhouse emissions of humanity (watch the rising temperature anomalies around the world here). Notably two important features of this human-induced climate warming for glaciers are long term mass loss (mostly melting) and occurrence of extreme events.

Figure 1. Monthly global surface air temperature anomalies relative to a 1981-2010 reference period. Source: ECMWF. https://climate.copernicus.eu/surface-air-temperature-january-2019

Figure 2. February 2018-January 2019 global surface air temperature anomalies relative to a 1981-2010 reference period. Source: ECMWF. https://climate.copernicus.eu/surface-air-temperature-january-2019

Considering the first point. Long term changes in glacier mass (the amount of ice of earth) is undoubtedly shrinking (Figure 3). Reference glaciers (those with long records of observations of change) of western USA, Canada and Europe show the largest reduction of ice, though evidence from the Andes is also bad news ².

Figure 3. Cumulative mass change (m w.e.) relative to 1976. The mass balance estimates considered here are based on a set of global reference glaciers with more than 30 continued observation years for the time-period, which are compiled by the World Glacier Monitoring Service (WGMS) in annual calls-for-data from a scientific collaboration network in more than 40 countries worldwide.

Within the central Andes of Chile, remarkably strong autumn warming of ~0.5 °C/decade is found in combination with decreases in precipitation ³. Equally precipitation falling in the mountains under a warmer climate is more likely to fall as rain and not snow, as has been seen in other parts of the world. Therefore climate change can potentially have a double-negative effect upon the health of glaciers, especially in regions, such as central Chile, that are sensitive to amount of rain falling seasonally.

Equally, the climate change has seen a rise in extreme events. Drought, heatwaves, hurricanes, to name a few…

The start of 2019 saw just this is South America (Figure 4) when Santiago’s record temperature rose to 38.3 °C and many parts of Patagonia saw temperatures in the high 30’s. These kind of events are equally likely to cause large scale, rapid icemelt which may also make hazards like glacier lake outburst floods ^4,5.

Figure 4. Extreme climatic events of early 2019 in South America. Source: MeteoChile Blog.

Cited information:

¹ IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.
² WGMS (2017, updated, and earlier reports): Global Glacier Change Bulletin No. 2 (2014-2015). Zemp, M., Nussbaumer, S. U., Gärtner-Roer, I., Huber, J., Machguth, H., Paul, F., and Hoelzle, M. (eds.), ICSU(WDS)/IUGG(IACS)/UNEP/UNESCO/WMO, World Glacier Monitoring Service, Zurich, Switzerland, 244 pp., based on database version: doi:10.5904/wgms-fog-2018-11. Available at: https://wgms.ch/faqs/
³ Burger, F., Brock, B., & Montecinos, A. (2017). Seasonal and elevational contrasts in temperature and precipitation trends in Central Chile 30-35° S between 1979 and 2015. Global and Planetary Change.  162. pp. 136-147. ISSN 0921-8181
⁴ Glaciers and climate change: Interview with Gino Casassa. Patagon Journal – 09 March 2018 Available at: http://www.patagonjournal.com/index.php?option=com_content&view=article&id=4062%3Aglaciers-and-climate-change-interview-with-gino-casassa&catid=78%3Amedioambiente&Itemid=268&lang=en
⁵ R. Wilson, S. Harrison, J. Reynolds, A. Hubbard, N.F. Glasser, O. Wündrich, P. Iribarren Anacona, L. Mao, S. Shannon (2019) The 2015 Chileno Valley glacial lake outburst flood, Patagonia. Geomorphology. 332.51-65.https://doi.org/10.1016/j.geomorph.2019.01.015.

Written by Thomas Shaw.
Edited by Equipo Glaciar.