Climate change declined snowpack in Northern Hemisphere between 1981, 2020: Study

NEW DELHI: Human-caused climate warming has declined snowpack in the Northern Hemisphere between 1981 and 2020, with the sharpest losses of about 10-20 per cent per decade seen in the southwestern and northeastern United States, as well as in central and eastern Europe, new research published in the Nature journal suggested.

Snowpack refers to the accumulated snow on the ground following snowfall and tends to not melt for a long time, owing to below-freezing temperatures.

Consisting of multiple layers, the snow mass compresses and hardens under its own weight. Researchers said that warm winters are known to favour rain over snow, increase snowmelt and reduce snow cover, which can have implications for water security and wider ecosystems. This study's findings have potential water security implications for "hundreds of millions of people in North America, Europe, and Asia who depend on snow for their water that continued warming will amplify", they said.

They said that while seasonal snow cover has been predicted to indicate effects of human-induced climate change, consistent warming trends have not been seen for snowpack loss, even as they have been observed at hemispheric, continental and river basins scales.

The researchers from Dartmouth College, New Hampshire, US, examined the effects of climate warming on snow by combining observations of March snow mass levels in the Northern Hemisphere along with temperature and precipitation data. They found that human-induced warming contributed to snowpack decline between 1981 and 2020.

However, owing to snow's nonlinear sensitivity to temperature, snow loss has not been widespread to date, they said. The researchers pointed out that snow becomes more sensitive to melting when winter temperatures exceed minus 8 degrees Celsius, and that about 20 per cent of the Northern Hemisphere's snow mass is found in locations with winter temperatures in this range.

All these locations may be at threat of increasing snow losses in the future. It is also this 20 per cent that "exists around - and provides water for - many of the hemisphere's major population centres that has diminished," they said. "(These losses) leave population centres suddenly and chronically short on new supplies of water from snowmelt."

Their results highlighted that around 80 per cent of the Northern Hemisphere's population lived near river basins that are snow-dependent for freshwater, which could see sharp spring runoff declines that lead to water availability challenges. Despite having examined Indian river basins with headwaters in the Himalaya, such as the Ganges, Brahmaputra and Indus, the researchers could not make confident claims on snowpack trends in the region, when PTI reached out to them enquiring about India-specific figures.

They attributed this partly to "substantial disagreement" across datasets and climate models, arising out of challenges of measuring snowpack in a region of such complex terrain.

The authors proposed that using data on snow mass from multiple sources may be better at identifying losses than a single dataset, as their findings suggested, and can provide a higher degree of confidence if trends are identified. The findings showed that snow losses are attributable to human-induced climate warming, which are likely to accelerate in the future and lead to water availability challenges, the researchers concluded.