Globally, glaciers lost 298 gigatonnes of ice every year between 2015 and 2019— a 31% increase over the rate of mass loss seen 15 years ago
A recent study, published in science journal Nature, revealed the world’s glaciers have lost 298 gigatonnes of ice annually between 2015 and 2019. The study is important because it extensively validates the estimates against in-situ observations using independent, high-precision measurements and presents the first globally complete and consistent analysis of glacier mass change.
The study titled, ‘Accelerated global glacier mass loss in the early twenty-first century’ was conducted by an international research team led by ETH Zurich and the University of Toulouse. It analysed around 2.2 lakh glaciers, excluding Greenland and the Antarctic ice sheets.
Accelerated glacier retreat
According to the study, between 2000 and 2019, the world’s glaciers lost 267 gigatonnes of ice per year on average. The rate though has accelerated consistently and significantly since the turn of the century from around 227 gigatonnes per year between 2000 and 2004 to around 298 gigatonnes between 2015 and 2019.
Glacial melt led to 21% of the observed rise in sea levels during this period, it noted. Considering all meltwater ultimately reaches the ocean, the contribution of glacial melt to sea-level rise was 0.74 mm per year.
As per the study, nearly half of the rise in sea levels is attributable to the thermal expansion of water as it heats up, with meltwater from the Greenland and Antarctic ice sheets.
It also revealed that seven glacierised regions account for 83% of the global glacier mass loss. Among the fastest melting glaciers are those in Alaska, the Greenland Periphery, Arctic Canada North and South. The profound effect can also be seen in the Antarctic and Subantarctic, High Mountain Asia (composed of Central Asia, South Asia West and South Asia East) and the Southern Andes.
“The situation in the Himalayas is particularly worrying,” said Romain Hugonnet, lead author of the study and researcher at ETH Zurich and the University of Toulouse.
If Himalayan glaciers observe more retreating in the future, populous countries like India and Bangladesh could face water or food shortages in a few decades, he added.
The study also pointed out that there are certain regions – Greenland’s east coast, Iceland and Scandinavia – where the melt rates have slowed between 2000 and 2019. This is attributed to a weather anomaly in the North Atlantic that caused higher precipitation and lower temperatures between 2010 and 2019, thereby slowing ice loss.
The same phenomenon, known as the Karakoram anomaly, was observed in the mountain range which is currently disappearing. The study found out that prior to 2010, glaciers in the Karakoram mountain range were stable and in some cases, even growing. However, the researchers’ analysis revealed that Karakoram glaciers are now losing mass as well.
Reduced uncertainties in data
The researchers used imagery captured onboard NASA’s Terra satellite, which has been orbiting the Earth once every 100 minutes since 1999 at an altitude of nearly 700km.
Terra is home to Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) – a multispectral imager with two cameras that record pairs of stereo images, allowing researchers to create high-resolution digital elevation models of all the world’s glaciers.
The team used the full archive of ASTER images to reconstruct a time series of glacial elevation, which enabled them to calculate changes in the thickness and mass of the ice over time.
The researchers independently computed surface elevation time series for about half a billion images, with an average of 39 independent observations per image between 2000 and 2019.
The way ahead
The study did not delve into the reasons behind the glacial retreat. However, many studies have pointed out climate change, global warming and human activities as the root of this phenomenon.
Regardless of altitude or latitude, glaciers have been melting at a high rate since the mid-20th century and steps need to be taken to control it.
According to co-author Daniel Farinotti, head of the glaciology group at ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, “Our findings are important on a political level. The world really needs to act now to prevent the worst-case climate change scenario.”