It's no secret that glaciers are becoming rarer and smaller in our warming world, but it's hard to understand the extent of that ice loss. Now, a comprehensive study has put a number to it, by combining field observations on the ground and satellite data. The team found that between 1961 and 2016, glaciers globally lost a total of over 9 trillion tonnes of ice, contributing significantly to sea level rise.

The biggest loser of that 55-year period was Alaska, which is down more than 3 trillion tonnes of glacial ice. Greenland comes in second, having shed 1.237 trillion tonnes, followed closely by the Southern Andes at 1.208 trillion. The Russian and Canadian Arctic regions also lost over a trillion tonnes each.

Of the 19 glacierized regions studied, only one actually gained ice during that time. Southwest Asia managed to put on an extra 119 billion tonnes of ice. Unfortunately that's a mere drop in the ocean – after all, the neighboring region of Southeast Asia effectively canceled it out by losing 112 billion tonnes.

And all that ice has to go somewhere. Melting glacial ice is considered the second-biggest contributing factor to rising sea levels, after warming waters. In this case, the team calculated that glacial ice loss has raised the global sea level by 27 mm (1 in) in that time. Worse still, these processes seem to be speeding up.

"While we can now offer clear information about how much ice each region with glaciers has lost, it is also important to note that the rate of loss has increased significantly over the last 30 years," says Michael Zemp, lead researcher on the study. "We are currently losing a total of 335 billion tonnes of ice a year, corresponding to a rise in sea levels of almost 1 mm per year."

To make these calculations, the team examined 19,000 individual glaciers in 19 regions around the world, estimating the changes in ice thickness over the past half-century. The outlines of glaciers were provided from satellite data from the ESA's Climate Change Initiative and GlobGlacier project. Other satellites provided topographical data that helped the team build digital elevation models, along with measurements taken from ground teams over the decades.

Glacial ice loss is important to track for many reasons. A better understanding of the mechanisms behind it helps scientists build more accurate climate models, and can help in the planning for run-on disasters, such as floods or water shortages after they're gone.

The study was published in the journal Nature.

Source: ESA

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