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 say.
Researchers from Newcastle University in the UK have identified a large scale circulation system — or vortex — centred over the Karakoram mountain range.
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, a mountain range in Central Asia.
This induces an anomalous cooling in summer, which is different to the warming seen over the rest of the Himalayas, researchers said.
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, they said.
“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 Hayley Fowler, professor at Newcastle University.
“Most climate models suggest warming over the whole region in summer as well as in winter,” said Mr. Fowler.
“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,” he said.
Researchers said that it is not known whether climate change will affect this circulation system and what the effect of sudden shifts might be.
However, the circulation system is currently providing a dampening effect on global warming, reducing glacial melt in the Karakoram region and any change will have a significant effect on ice melt rates, which would ultimately affect river flows in the region, they said.
Usually, glaciers oscillate between growth and retreat.
Snow falls on the peaks and gradually compacts and turns to ice while lower down the glaciers lose ice to melting and evaporation.
If snowfall equals snow-melt, the glacier is in equilibrium but global warming has tipped the balance so that most of the world’s glaciers are shrinking.
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 Himalaya are warming, and vice versa, researchers said.
Over recent decades, these vortex-monsoon interactions have resulted in stormier conditions over the Karakoram.
“This vortex provides an important temperature control,” said Newcastle University’s Nathan Forsythe, lead author of the study published in the journal Nature Climate Change .