What do glacial mass balance records tell us?

Records of glacial mass balance provide us with a clear view of how glaciers in most regions have changed over time. Whilst these records predominantly exist in the northern hemisphere, there also exist good studies elsewhere as well. By knowing how the mass balance has changed, climate change influences can be inferred as well as other factors such as sea level rise correlated. 

As Zemp et al. (2009) discuss in their review of the WGMS programme, from looking at the data of 30 continuously recorded ‘reference’ glaciers there has been an evident trend of increasing glacial mass loss over the past several decades:

“...continuous measurements since 1976 show an (arithmetic) average annual mass loss of 0.58mw.e. for the decade 1996–2005, which is more than twice the loss rate for the period 1986–95 (0.25mw.e.), and more than four times the rate for the period 1976–85 (0.14mw.e.).”

Not only that, but this trend is clearly set to continue; with the paper stating that a preliminary value of -1.30 m w.e for the year 2006 is recorded (which therefore breaks the record for highest annual mass loss yet). Whilst this data provides clear evidence, starker evidence is expressed in the paper:

“The vast ice loss since the mid-20th century has already led to the disintegration of many glaciers within the observation network, including Lower Curties and Columbia 2057 (US), Chacaltaya (BO), Care`ser (IT), Lewis (KE) and Urumqihe (CN)...”

Figure 1. Global glacier mass changes from 1945 to 2006. The cumulative mean specific mass balance (left y axis) of the reference glaciers and of four different sampling/averaging approaches (see text) are shown together with the number of available observations (right y axis) from reference (black) and other (grey) glaciers. Source: data from the WGMS.

The paper also explains the main processes behind this drastic reduction in glacial mass. Whilst changes in mass balance provide a climatic signal that is made up of several different sources, including solar radiation, air temperature, precipitation, wind etc... air temperature thereby has an integral part to play as it is related to the radiation balance, turbulent heat exchange and solid/liquid precipitation ratio (Zemp et al. 2009). The point of this is to show the clear effect that a change in climatic conditions and temperature has on a glacier, in most cases.

To try and make this point clearer, for a temperate glacier; initial changes in climatic conditions would cause a change in mass balance, followed by a return towards zero mass balance change values. This return to stable glacier mass conditions happens as a result of the glacier surface area adapting to the new climate (shrinking with warmth and vice-versa). However, when we see in these records that the negative mass balance is increasing whilst the surface area decreases it is evident that climatic forcing continues to affect glaciers and perhaps even shows the effects of positive feedback; such as changes in surface albedo, more intense turbulent fluxes from greater rock outcrops, or changes in the extent of the equilibrium line altitude (ELA).

Additionally to the WGMS report, Norway provides the only long term, nationally funded records, of changes in the mass balance of Norwegian glaciers and as such provides a useful, high resolution record, of growth and retreat from past to present. The vast majority of mass balance records in Norway go back to the early 1960s and are largely uninterrupted. A study by Nesje et al. (2008) shows that the RegClim climate scenario study estimated a rise of 2.3°C in mean summer temperatures and an increase of precipitation by 16% during accumulation season in Norway up to 2100. This rise in summer temperatures and increase in winter precipitation is in turn expected to create melting conditions of ~140±30 m w.e by 2100 and thus a net loss of glacier ice.

The subsequent figure of 98% reduction in the number of Norwegian glaciers by 2100 makes for hard reading!

Figure 2. Briksdalsbreen, a western outlet glacier from Jostedalsbreen, has retreated 300 m between 1997, when it was located at the outlet of the lake, and July 2006. Photo: Atle Nesje. (Nesje et al. 2008)

Introduction to the blog

Before going into the more specific issues that this blog will cover, it is first important to give a summary of what I hope to achieve! This blog will seek to explore the sensitivity of glaciers globally, to both climate change in the past, as well as to the warming of climate today. Alongside this, by looking at how representative of a changing climate glaciers have been both before and now, we can assess the reliability for looking at future shrinking (or growth). The data on changes in glacial mass balance and other indicators of change will be sourced from a range of academic papers, and analyses of different phenomena interpreted in this blog. As well as the use of academic material, a look at how much of this information feeds through to more mainstream and social media and whether it is always correctly interpreted will be taken.

The significance of knowing how glaciers will behave in the future is important, considering the impact that the loss of these environments could have as both a freshwater resource for many people (particularly in Central Asia) and as an important habitat for many different flora and fauna. Knowing how glaciers in the past expanded and shrunk also helps us to reconstruct past environments. As well as this, by knowing the sensitivity of glacial environments to varying degrees of temperature change, we can see how vulnerable they are to our present anthropogenic warming.

A useful resource to initially explore is the University of Zurich’s World Glacier Monitoring Service (WGMS) report on Global Glacier Changes which provides an accessible set of data on glacial growth and reduction in the long term. By first seeing how trends in glacial growth/reduction have been up to the present day, an appreciation of how significant current reductions are can be made. This blog will aim to move on from this face-value data; and show many important interpretations and academic insights about glacial change!

Figure 1. Global measure of increasing negative mean cumulative specific mass balance as millimetres water equivalent (mm w.e.) over the last few decades. (Zemp et al. 2008)