Mountain treelines are rising in response to the climate crisis, a study has found. Scientists from the Southern University of Science and Technology in Shenzhen, China, used remote sensing to map the highest points of patches of tree coverage on mountains. They found that 70% of mountain treelines had moved uphill between 2000 and 2010. On average, treelines moved upwards by 1.2 metres (4ft) a year, but the shift was greatest in tropical regions, with an average increase in elevation of 3.1 metres a year – and in all regions they found the rate of change was accelerating. In total, the researchers tracked almost 1m km (620,000 miles) of treeline across 243 mountain regions around the world. Treelines sometimes move in response to human activities such as changes to land use. However, in this study the researchers focused on closed-loop mountain treelines, which encircle the very tops of mountains and are mostly isolated from human activities. The researchers found that the treelines still moved, which demonstrates that they are sensitive to changes to climate beyond human influence. It is not clear what the consequences of treeline movement will be. Rising temperatures will enhance growth above the level of the current treeline: more trees mean more carbon will be removed from the atmosphere. It could also expand the habitats of some forest species. However, upward movement of treelines reduces the area of tundra, which puts alpine species at risk of extinction and may affect water supply to areas that rely on it. “Mountain treelines are important indicators of the impact of climate change on upland ecosystems,” the researchers wrote in the journal Global Change Biology. “Our work … has important implications for biodiversity, natural resources, and ecosystem adaptation in a changing climate.”