A small glacier group with an outsized impact
Just 3.2% of the world’s glaciers end in lakes, oceans or ice shelves, yet that comparatively small group accounted for more than half of global glacier ice loss between 2000 and 2019, according to new research published in Nature Communications.
The study examined 216,502 glaciers worldwide, excluding the Greenland and Antarctic ice sheets. Researchers found that glaciers terminating in water lost an average of 134 billion metric tons of ice each year during the two-decade study period. Their result focuses attention on a class of glaciers that is both physically distinctive and especially important for projections of environmental change.
The glaciers included in the analysis are generally larger than glaciers that end on land. Together, glaciers ending in lakes, oceans or ice shelves cover more than half of the world’s glacier area. But the research indicates that size alone does not explain their importance.
Lake-ending glaciers lost ice faster
Glaciers that end in lakes stood out in particular. Relative to their size, they lost ice about 57% faster than land-terminating glaciers over the same period, the researchers found.
The study’s authors say the reasons for this difference are not yet fully resolved. Lake water may contribute by melting ice beneath the waterline, while glaciers that meet lakes can also lose substantial blocks of ice at their fronts through calving. The size and shape of the glaciers may also matter, and the effects could be combined.
That uncertainty is consequential because glacier lakes are becoming more common in a warming climate. Understanding how those lakes interact with adjacent ice could improve assessments of future ice loss and related hazards.
Why glacier classification matters
Many glacier-change models do not yet fully account for glaciers that terminate in lakes. The new global classification distinguishes glaciers by whether they end on land, in lakes, in oceans or at ice shelves, allowing researchers to compare ice flow and loss across all four groups.
That framework could help improve estimates of sea-level rise, freshwater resources and natural hazards. The authors note that knowing where a glacier ends is more than a geographic detail: the contact between ice and water can change how quickly a glacier loses mass.
The results also underscore why global glacier assessments need to look beyond total ice area or the number of glaciers. A relatively small subset can have a disproportionate effect on the overall balance of glacier ice, especially when its terminus is exposed to water.
Questions for the next phase of research
The researchers say a key next step is determining why lake-ending glaciers are losing ice so rapidly. Untangling the respective roles of lake water, glacier geometry and calving would help scientists represent those processes more accurately in future models.
For communities and decision-makers, the work has implications beyond long-term climate indicators. Changes in glacier behavior can affect water availability and the risk profile of mountain landscapes. Better classification and modeling of water-terminating glaciers may therefore sharpen projections used in planning for both gradual and sudden impacts.
The study does not suggest that land-terminating glaciers are unimportant; glacier loss is a broad global issue. Instead, it identifies a concentration of loss that models and monitoring systems need to capture. In a changing climate, the glaciers where ice meets water may be among the most consequential places to watch.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
