The Karakoram Anomaly: Is it real?
In recent years with sharp summer sea ice decline, the Arctic seems more sensitive to climate warming than elsewhere on Earth. But are other frozen features of Earth changing too? Notably, most of the world's glaciers are also getting smaller—except for a few stubborn ones, such as in the Karakoram area of the Himalaya. Why are these glaciers not retreating?
The climate of the Hindu Kush-Karakoram-Himalaya range, stretching over 2000 kilometers (1200 miles), is highly variable and governed by microclimates. “Glaciers here seem not to react in the same way as the majority of glaciers in the world,” said Christoph Mayer, a glaciologist from the Bavarian Academy of Sciences and Humanities. Generally, the glaciers reaching into Tibet and Nepal have lost a significant amount of mass and area. Its western end, stretching into Pakistan, has been relatively stable, pegging the phrase “Karakoram Anomaly.”
Usually, glaciers oscillate between growth and retreat. At the highest elevation, snowfall adds to the glacier's mass. During several years this snow compacts and turns to ice, and under its own weight, gravity pulls the glacier into a slow drift. In lower elevations, glaciers lose ice to melting and evaporation. If snowfall equals snowmelt, the glacier is in equilibrium. Increased snowfall advances a glacier’s extent, while increased melting forces glacial retreat. Yet in this most glaciated part of the world outside of the polar regions, some glaciers have not changed, while some have even advanced. Mayer discovered blankets of debris—widely present in the Karakoram glaciers—may be key to their alleged stability.
"Debris-covered glaciers react very differently to climate change," Mayer said, “and this needs to be understood.” Unraveling a glacier’s complex role in water supply is crucial for countries like Pakistan, where snow and glacial melt feeds more than 50 percent of the Indus River flow, irrigating a highly agricultural economy.
Very thin debris, a coat of dark color on snow, absorbs more solar energy, leading to faster melt. This is apparent in the Rocky Mountains. But in the Karakoram, debris is much thicker, deposited on the glacier surface by avalanches and rockfalls, then melting out of the ice during its journey down the valley. “As soon as the thickness reaches a certain value, the layer insulates the ice,” Mayer said. By measuring the amount of heat moving within the debris layer, it became apparent not enough heat traveled down to melt the ice beneath. So for some areas within the Karakoram, debris is staving off glacial melt. But what about the overall picture? To this day there has been no accurate mass balance measure in the Karakoram. Satellite imagery of a glacier helps determine its length and breadth, but to appreciate the details of ice gain and loss field work is crucial—specifically, mass balance measurements that measure the difference between snow accumulation and snow and ice melting.
Sticking with the facts
These field studies involve exposing researchers to the extremes of the terrain. “Field work in the Karakoram is not easy,” Mayer said. It is a four to four day trek just to reach the snout of Baltoro Glacier. Debris-covered glaciers are rough and loose underfoot. “There are boulders several meters thick in diameter,” Mayer added. “Everything is unstable here.” Researchers stick wooden poles of 2 meters (6.6 feet) length, connecting them for a total length of 12 meters (39 feet), into the ice to gauge a glacier’s velocity and the change in height. Is the surface sinking or rising?
The so-called Karakoram Anomaly doesn’t convince Mayer. “Look at the details,” he added. When Mayer turned to the Baltoro Glacier, his doubts were justified. The glacier’s lower portion, the snout, is debris-covered and appears to be climate resistant with zero retreat, but the clean white top has a melt rate of up to 4.5 meters, while the surface sinks by more than 0.5 meters every year. “Basically our research showed how much ice was lost during summer and how much snow was deposited in the high regions,” Mayer said. The Baltoro Glacier mass balance measurements are just a start on getting a clearer picture of how the entire system works. Mayer said, “We need to take the debris cover into account if we want to calculate future ice resources and melt water production under a changing climate.” The devil is indeed in the details.
Minora, U. et al. 2013. 2001–2010 glacier changes in the Central Karakoram National Park: a contribution to evaluate the magnitude and rate of the “Karakoram anomaly.” The Cryosphere Discussions 7, 2891–2941, doi:10.5194/tcd-7-2891-2013.