If mountain glaciers hold less ice than previously believed, what does that mean for people who depend on glaciers for water?

Globally, almost two billion people rely on mountain glaciers and snowpacks as their main source of drinking water. Many also rely on glacier water for hydropower generation or agriculture, particularly in the dry season. But the vast majority of glaciers around the world are losing more mass than they gain during the year as the climate warms, and they are slowly disappearin g . That will profoundly affect these populations . These communities need to know how long their glaciers will continue to provide water and what to expect as the glaciers disappear so they can prepare. In most places, we found significantly lower total ice volumes than previous estimates indicated. In the tropical Andes, from Venezuela to northern Chile, for example, we found that the glaciers have about 23 percent less ice than previously believed. This means downstream populations have less time to adjust to climate change than they may have planned for. Even in the Alps, where scientists have a lot of direct ice thickness measurements, we found that the glaciers may have eight percent less than previously thought. The big exception is the Himalayas. We calculated that there may be 37 percent more ice in these remote mountains than previously estimated. This buys some time for communities that rely on these glaciers, but it does not change the fact that these glaciers are melting with global warming. Policymakers should look at these new estimates to revise their plans. We do not provide new predictions of the future in this study, but we do provide a better description of what the glaciers and their water supplies look like today.

How do these finding affect estimates of future sea level rise?

First, it’s important to understand that melting glaciers are only one contributor to sea level rise as the climate warms. About one-third of today’s sea level rise is due to thermal expansion of the ocean – as the ocean warms, water expands and takes up more space. The other two-thirds come from shrinking mountain glaciers and ice sheets . We found that if all the glaciers, not including the big ice sheets in Greenland and Antarctica, were to melt entirely, sea level would rise by about 10 inches instead of 13 inches. This may sound like a large difference, considering the size of the ocean, but you have to put things in perspective. A complete disintegration of the Antarctic ice sheet would contribute 190 feet to sea level and the Greenland ice sheet would contribute 24 feet . The three inches that we are talking about in this study do not call into question current projections of sea level rise.

Why has it been so hard to figure out the ice volume of glaciers, and what did your study do differently?

You might be surprised by how much is still unknown about some of the basic characteristics of remote mountain glaciers. Satellites have transformed our understanding of glaciers since the 1970s, and they provide an increasingly clear picture of glacier locations and surface area . But satellites cannot see “through” the ice. In fact, for 99 percent of the world’s glaciers, there is no direct measurement of ice thickness. Scientists have spent more time mapping the Greenland and Antarctica ice sheets and the terrain below, and we have much more detailed volume measurements there. NASA, for example, dedicated an entire airborne mission, Operation IceBridge , to collect ice thickness measurements in Greenland and Antarctica.

Mountain Glaciers May Hold Less Ice Than Previously Thought: What That Means

Mountain glaciers are essential water sources for nearly a quarter of the global population. But figuring out just how much ice they hold – and how much water will be available as glaciers shrink in a warming world – has been notoriously difficult.

In a new study, scientists mapped the speed of over 200,000 glaciers to get closer to an answer. They discovered that widely used estimates of glacier ice volume may be off by about 20 percent in terms of how much Earth’s glaciers outside the Greenland and Antarctic ice sheets could contribute to sea level rise.

Mathieu Morlighem, a leader in ice sheet modeling and a co-author of the study, explains why the new results hold a warning for regions that rely on glaciers’ seasonal meltwater, but barely register in the big picture of rising seas.

BECOME A MEMBER

Mountain Glaciers May Hold Less Ice Than Previously Thought: What That Means

In a new study, scientists mapped the speed of over 200,000 glaciers to get closer to an answer.

Read Latest News and Breaking News at The Quint, browse for more from news and world

Topics: Climate Change Glacier sea level rise