Alaska Glaciers Leading to Global Sea Level Rise

Like in the Arctic, Antarctic and even Canada, glaciers in Alaska are melting. Now, new research reveals that like their famous brethren, they may make large contributions to global sea level rise.

In fact, these glaciers are adding enough water to the Earth's oceans to cover the state of Alaska with a one-foot thick layer of water every seven years, researchers say. What's more, glacier loss from Alaska is showing no signs of slowing down.

"The Alaska region has long been considered a primary player in the global sea level budget, but the exact details on the drivers and mechanisms of Alaska glacier change have been stubbornly elusive," lead author Chris Larsen, a research associate professor with the Geophysical Institute at the University of Alaska Fairbanks (UAF), said in a news release.

In order to pinpoint its role in rising sea levels, for 19 years, the UAF and US Geological Survey (USGS) research team analyzed surveys of 116 glaciers in the Alaska region, including those in the southwest Yukon Territory and coastal northern British Columbia. They estimated ice loss from melting and iceberg calving, using lidar altimetry data collected as part of NASA's Operation IceBridge.

Although mountain glaciers hold less than one percent of the Earth's glacial volume - the rest is found in Antarctic and Greenland ice sheets - they cause nearly one-third of current sea level rise due to melting, according to prior research. This includes Alaska's melting mountain glaciers.

"Alaska has been identified for years as a big contributor in global sea level rise, but until now we have not had a clear understanding of the processes responsible for the rapid changes of these glaciers," added study co-author Shad O'Neel, a geophysicist with the USGS Alaska Science Center in Anchorage.

During the study, scientists compared the observed changes of two main types of glaciers: those that end on the land, and those that end in lakes or the ocean, referred to as calving (or tidewater) glaciers. Any glacier can lose mass through surface melting, but only those ending in water can lose ice through iceberg calving.

"We've long wondered what the contribution of iceberg calving could be across the entire state," O'Neel noted.

For example, Columbia Glacier in Prince William Sound has retreated more than 19 kilometers (12 miles) - mostly because of iceberg calving - and thinned by more than 450 vertical meters (1,500 vertical feet) since 1980. Now, hopefully researchers can determine how this melting glacier and others in Alaska are contributing to global sea level rise.

Using the newly enabled ability to separate glaciers into different categories using the lidar data, the researchers made some surprising discoveries.

"Our results show the regional contribution of tidewater glaciers to sea level rise to be almost negligible," Larsen explained. "Instead, we show that glaciers ending on land are losing mass exceptionally fast, overshadowing mass changes due to iceberg calving, and making climate-related melting the primary control on mountain glacier mass loss."

"This work has important implications for global sea level projections. With improved understanding of the processes responsible for Alaska glacier changes, models of the future response of these glaciers to climate can be improved," Larsen said.

"Thinking about the future, it means that rates of loss from Alaska are unlikely to decline, since surface melt is the predominant driver, and summer temperatures are expected to continue to increase. There is a lot of momentum in the system, and Alaska will continue to be a major driver of global sea level change in upcoming decades," he added.

The findings were published in the journal Geophysical Research Letters.

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