Almost 10 percent of the world’s land mass is currently covered with glaciers. The largest concentrations are in the Antarctic and Arctic, followed by the Himalayas, which house about 35,000 square kilometers (13,514 square miles) of glacial ice. This is why the Himalayas are often referred to as the “Third Pole.”
Glaciers store about 75 percent of the world’s freshwater and act as natural reservoirs, storing water in the winter and meting it out in the summer as the ice slowly melts. Glacial ice can be hundreds of thousands of years old, offering a wealth of data to climate scientists who can drill ice cores and examine long-term climate records, helping them assess changes across millennia.
Black carbon – particulate matter that in South Asia comes mainly from the burning of wood and waste and from cooking fires, or from coal-burning and diesel exhausts – falls on snow and darkens the surface, in the process reducing reflectivity and causing the surface to absorb more heat.
Shrinking glaciers due to global warming have become a concern worldwide. Glaciers react quickly to changes in air temperature and precipitation. Since the early twentieth century, with few exceptions, glaciers around the globe have been retreating at unprecedented rates. Most mountain glaciers have in fact been retreating since the late 1800s, and global sea level has risen about 30 centimeters since then. Why are scientists concerned about receding glaciers? There are a number of reasons:
- Melting of glaciers and ice caps will have global effects on sea level rise. Current estimates are that they will contribute about 40 to 150mm (depending on the greenhouse gas scenario and climate model used) to sea level rise by 2100. Glacier recession and thermal expansion of the ocean together account for 75% of today’s observed sea level rise.
- Flow characteristics of glacier-fed rivers are impacted by receding glaciers, increasing the risk for glacial lake outburst floods and overall flood severity and frequency. Such events endanger lives and threaten livelihoods, wildlife, agriculture, forestry, and drinking water supplies.
- In areas that are heavily dependent on water runoff from glaciers that melt during the warmer summer months, a continuation of the current retreat will eventually deplete the glacial ice and substantially reduce or eliminate runoff. A reduction in runoff will affect the ability to irrigate crops and will reduce summer stream flows necessary to keep dams and reservoirs replenished. For a landlocked country like Nepal, which relies on hydropower generation as a vital source of national income, the prospect of an eventual decrease in the discharge of rivers is unsettling as well.
- Many species of freshwater and saltwater plants and animals are dependent on glacier-fed waters to ensure the cold water habitat to which they have adapted. Some species need cold water to survive and to reproduce. Reduced glacial runoff can lead to insufficient stream flow to allow these species to thrive.
Measuring the extent of Himalayan glacial recession is complex, and reliable and consistent data has been scarce in comparison to some other glacial regions, in part due to accessibility issues at the extreme elevations and in the very remote and rugged terrain found in this region. Himalayan glaciers are retreating at rates ranging from 10 to 60 meters per year, with some high altitude valley glaciers shifting as much as 100 meters within the last fifty years, according to the International Centre for Integrated Mountain Development (ICIMOD).
There are many good resources online to learn more about glaciers, glacial melt, glacial lakes, and the threat of glacial lake outburst flooding. A few resources are listed to the right, and more can be found in the Resources section of our site. Just click on the tab in the resources labeled “All About Glaciers”!