Contributions to Sea Level Rise: Mountain Glaciers & Ice Caps

In this momentous week where Donald Trump has been elected as President of the USA; Climate Scientists, and all those who believe in the argument that frankly among climate scientists is no longer an argument, it is worrying to point out this video where Trump dismisses Climate Change as a hoax or just ‘weather’. A good point of view piece is from Green MP Caroline Lucas on why Trump's election is a worry. On the off chance Donald is reading this blog (…) I will point out the Climate Central website which projects the impact of SLC on coastal cities including his beloved New York… 

But I shall not dwell on this and move onto one of the major contributors to SLR, that from glacier melting. To clarify this I am following the IPCC in distinguishing between the Antarctic and Greenland Ice Sheets (see map below) and all other glaciers and ice caps, this post focuses on these smaller glaciers and their contributions to SLR both during the instrumental period and in the future.

Location of the major mountain glaciers and ice caps (1-18) that contribute to SLC, Greenland & Antarctica (19 & 20) are not discussed in this post. Source

Mountain glaciers and regional ice caps have been observed to be one of the most important recent contributors to SLC. The video below shows how Glacier National Park, USA could become no Glacier National Park by 2050. 

This picture is repeated across mountain glaciers and ice caps around the world, dynamical and extreme retreat has occurred in most mountainous regions since the 1850s, producing meltwater that contributes to SLC. As the graph below shows recent SLC contribution is similar to that of the Greenland and Antarctic Ice Sheets combined.

This paper from Jacob et al., (2012) analyses the contribution of Glaciers and Ice Caps to SLC and suggests a value of 0.41±0.08 mm/yr as its contribution to the GMSL rise. This paper heralded a distinct advancement in the understanding of these smaller ice sources and their contribution to SLC by using GRACE altimetry to constrain mass balance (whether a glacier is advancing or retreating). It shows an acceleration across a number of regions including Alaska but suggests a decreased influenced from the Himalayas. This is due to enhanced spatial resolution as they took sub regions of the Himalayas compared to seeing the Himalayas as one region as done by Matsuo & Heki (2010), which resulted in a perceived overestimate of Himalayan contribution. This is a forward step for understanding contribution to SLC from these smaller, spatially disparate sources that have had significant impact in recent times to SLC. Further support for the large contribution to recent SLC is given by Gardner et al., (2012) who suggest current contribution of 29±13% to global SLR is from these Glaciers and Ice caps. Ice loss is particularly strong in the Andes, and Arctic Canada and Alaska (see below) and as my post from a couple of weeks ago suggests, this could cause far greater local and regional SLC.

Contributions of different glaciated regions to SLC. Source

Future Contribution

As significant ice mass loss continues this will contribute to global SLR, however as glaciers shrink in size they are likely to come to a point when they reach a balance. Some glaciers such as those remaining in Africa are likely to disappear completely although their contribution to SLR is likely to be negligible. Radic & Hock (2011) present a study suggesting many will have experienced serious loss but some may only lose 20% of ice mass. GMSL contribution by 2100 is expected to be 0.124±0.037m yet variable contributions and uncertainty mean that this is by no means certain. Therefore by 2100 the contribution may be almost negligible as melt may have stabilised due to lack of available ice to melt. In addition the effects on water availability, for instance billions of people rely on the Himalayas as the primary source of water could have severe consequences.

Projected volume (left axis) and Sea Level equivalent (right axis) of glaciers for a series of models until 2100. Source