A summer 'vortex' of cold air over the Karakoram, a large mountain range spanning the borders of India, Pakistan, and China, is causing the glaciers in the region to grow in spite of global warming, scientists have shown.
"While most glaciers are retreating as a result of global warming, the glaciers of the Karakoram range in South Asia are stable or even growing," said study co-author Hayley Fowler, Professor at Newcastle University in Britain.
In their study, published in the journal Nature Climate Change, the team reported the identification of a large scale circulation system — or vortex — centred over the Karakoram.
In winter, the vortex affects the temperature over the whole 2,000-kilometre mountain range, but in the summer the vortex contracts and has an effect only over the Karakoram and western Pamir, said the study.
This induces an anomalous cooling in summer which is different to the warming seen over the rest of the Himalayas.
This Karakoram vortex goes some way to explaining why the glaciers in this region are behaving differently to those in most other parts of the world, Fowler said.
"Most climate models suggest warming over the whole region in summer as well as in winter. However, our study has shown that large-scale circulation is controlling regional variability in atmospheric temperatures, with recent cooling of summer temperatures. This suggests that climate models do not reproduce this feature well," Fowler said.
The Karakoram anomaly was first described in 2005 and since then, scientists have been trying to determine what might be causing the expansion of glaciers in the region — which includes the world's second tallest K2 mountain peak.
Acting like a counter-weighted temperature control, the unique summer interaction of the Karakoram vortex and the South Asian Monsoon causes temperatures in the Karakoram and Pamir to cool while those in the Central and Eastern Himalayas are warming, and vice versa, according to the study.
"This vortex provides an important temperature control," lead author of the study Nathan Forsythe of Newcastle University said.
"It is, therefore, important to look at how it has changed and influenced temperature over the last century so we can better understand how a change in the system might affect future climate," Forsythe said.
"This is of huge importance in terms of food security because of the large populations that rely on water resources from snow and ice melt from the mountainous catchments to grow their irrigated crops in the Indus Plains of the Sindh and Punjab states and provinces of Pakistan and India," Forsythe added.