Scientists have been ringing alarm bells about the future of the Himalayas, known as “one of the world's most sensitive hotspots to global climate change.” Much of experts’ attention has been focused on the regions’ glaciers, which are melting at a deeply worrying rate. But a new study, published in the journal Global Change Biology, highlights another ecosystem trend: plant life across the Himalayas is expanding, possibly due to warming temperatures.

Led by Karen Anderson, a geographer at the University of Exeter, researchers took a close look at the subnival ecosystem of the Hindu Kush Himalaya mountains—an area that sits above the treeline and below the permanently snow-covered region. According to Michael Marshall of New Scientist, this zone experiences seasonal snow coverage; during warmer weather, small plants like grasses, shrubs and moss can grow there.

Because it sits at a high altitude and is difficult to reach, the Himalayas’ subnival zone has not been well studied. To circumvent the challenges posed by the area’s geographic location, Anderson and her colleagues turned to satellite data collected by NASA Landsat missions between 1993 and 2018. These images, taken high above the Earth, allowed the researchers to track patterns in vegetation coverage across four height brackets spanning between 4,150 and 6,000 metres above sea level.

The team’s observations varied at different heights and locations—not surprisingly, given that ecosystems in the Hindu Kush Himalaya region are “diverse due to the variety of complex climatic conditions, alongside stark variations in altitude and slope aspect,” according to the study. Overall, the researchers found “a weakly positive increase in the extent of subnival vegetation since 1993,” with the strongest trends emerging between 5,000 and 5,500 meters above seal level. In the area around Mount Everest, they observed a “significant increase” in vegetation across all four height brackets, according to the University of Exeter.

The study did not look at why vegetation growth is expanding in the Himalayas, but Anderson tells Marshall her “initial guess would be that the primary driver is temperature limitation being removed.” The warmer it gets, in other words, the more plants can grow in areas that were once too cold to be hospitable.

Just what this means for the Himalayan ecosystem is far from clear, but in an interview with CNN’s Amy Woodyatt, Anderson says the need to find out is “urgent.” The Himalayas’ glaciers feed into many of the world’s great rivers, with some 1.4 billion people depending on water sources that emanate from the mountains. Should these glaciers disappear, as one-third of them are predicted to do by 2050, food, water and economic security in the affected regions would be severely compromised. A more acute concern, however, is flooding. Melting glacial ice has led to the formation of lakes contained by unstable dams; as the lakes grow, so do the risks of breaches that could send catastrophic floods gushing into the valleys below.

The authors of the new report don’t know how the spread of vegetation on the mountains fits into this fragile ecosystem picture. Plants might absorb more heat than the bare ground, causing snow to melt more quickly, Anderson tells Marshall. But it is also possible that the vegetation retains moisture, thus helping to regulate the flow of water.

What the study authors do know, as Anderson explains to Woodyatt, is that “plants and the water cycle are coupled. Wherever you have plants growing, it changes the way the water cycle behaves in those areas."

In their report, the study authors call for further research into the Himalayas’ subnival zone, which is between five and 15 larger than the area of permanent ice and snow. Satellite data will likely continue to play an important role in future research, but on-the-ground studies are vital as well. “Overall,” the researchers write, “we need an improved functional understanding of the state and fate of subnival ecosystems.”