**Dr. Tom Matthews and Dr. Baker Perry, members of the National Geographic and Rolex Perpetual Planet Extreme Expedition to Mount Everest, work on the automated weather station at Everest Base Camp**

What is the weather like up on Mount Everest today? Last year a bunch of daredevil scientists and Sherpas laboured in the “death zone” and installed the world’s highest weather station, perched at 8,430 metres, just 400 metres short of Everest’s summit. But it nearly didn’t happen.

Having been stuck behind a queue of climbers heading for the summit, the 2019 National Geographic and Rolex expedition team were dangerously cold when they reached the location where the station was to be installed. “We paced back and forth, attempting to stave off frostbite as wind-chill temperatures hovered close to -30°C and our drill batteries became too cold to work,” said Loughborough University’s Tom Matthews on the Conversation

Luckily team member Phutasi Sherpa had enough body heat to warm up the batteries and get the drill going again, enabling the team to bolt their weather station to the side of the mountain.

As well as helping to keep climbers safe, the data from this extreme weather station is enabling scientists to directly monitor the jet stream and get a handle on how Himalayan climate is changing.

Preliminary measurements published in the Bulletin of the American Meteorological Society are already overturning assumptions, indicating that despite the sub-freezing conditions melting may even be possible on the summit.

Preliminary measurements published in the Bulletin of the American Meteorological Society are already overturning assumptions, indicating that despite the sub-freezing conditions melting may even be possible on the summit.

As the highest mountain on Earth, Mount Everest is an iconic peak that offers an unrivalled natural platform for measuring ongoing climate change across the full elevation range of Asia’s water towers. However, Everest’s extreme environment challenges data collection, particularly on the mountain’s upper slopes, where glaciers accumulate mass and mountaineers are most exposed. Weather stations have operated on Everest before, including the world’s previous highest, but coverage has been sparse in space and time. Here we describe the installation of a network of five automatic weather stations (AWSs), including the two highest stations on Earth (8,430 and 7,945 m MSL) which greatly improves monitoring of this iconic mountain. We highlight sample applications of the new data, including an initial assessment of surface energy fluxes at Camp II (6,464 m MSL) and the South Col (7,945 m MSL), which suggest melt occurs at both sites, despite persistently below-freezing air temperatures.

This analysis indicates that melt may even be possible at the 8,850 m MSL summit, and prompts a reevaluation of empirical temperature index models used to simulate glacier melt in the Himalayas that focus only on air temperature. We also provide the first evaluation of numerical weather forecasts at almost 8,000 m MSL and use of model output statistics to reduce forecast error, showcasing an important opportunity to improve climber safety on Everest. Looking forward, we emphasize the considerable potential of these freely available data for understanding weather and climate in the Himalayas and beyond, including tracking the behavior of upper-atmosphere winds, which the AWS network is uniquely positioned to monitor.

Mountains cover 25% of Earth’s land surface and their snow and ice stores act as water towers for more than a billion people worldwide. They are locations of especially hazardous weather extremes, and a natural observation platform from which to observe globally significant high-altitude winds. The climate is also warming at altitude more rapidly than the global mean, which makes these water towers vulnerable to accelerated melt . It is unfortunate, then, that continuous observations from automatic weather stations (AWSs) are biased toward lower, more accessible elevations. The problem is particularly apparent in High Mountain Asia (HMA), where only a handful of AWSs have been installed above 5,000 m MSL, an elevation above which almost 62,000 km2 of glacier area in HMA is located (around 63% of the total HMA glacierized area); above 6,000 m MSL nearly 11,000 km2 (around 11% of the glacierized area) is found, yet we were unaware of a single AWS in HMA still operating above this elevation when our project started (observations from 6,352 m MSL on Nepal’s Mera Peak ceased in November 2016).

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