At 11.15am on a blustery spring morning, Lori Bennett stands on an exposed bluff on the remote south Atlantic island of St Helena, holding a gigantic, wobbling balloon. The wind is roaring, waves are churning up a swell and the sea air is charged with industrial hydrogen pumped from a nearby outhouse and used for blowing up the inflatable.

The Met Office station manager, born in Northern Ireland and now living half a world away from his friends and family in Swindon, is a picture of calm in a drab boiler suit, old ski goggles and a flash hood he jokingly calls his “Star Wars outfit”. Moments later, he prepares to let the weather balloon slip from his fingers. Swinging it around, so that it lifts straight up rather than floating across the weather station car park, he is soon watching it jiggle steadily upwards before it disappears into the clouds.

“They’ve been known to scare the life out of pilots,” says Bennett, flipping his goggles off. “But out here in the middle of nowhere we don’t get many planes.” As well as launching the balloon in 45-knot winds that “can pull your arm off”, Bennett’s main worry is the hydrogen used to fill it. A spark of static could detonate the gas inside the warehouse and violently blow the doors clean off. “You wouldn’t walk away from that,” he says, matter-of-factly.

It affects people’s lives every day – we’re the frontline in Atlantic forecasting

Sometimes, it is easy to forget the lengths to which meteorologists go to bring us forecasts: telemetry instruments and synoptic codes don’t really figure in the chitchat of TV weather presenters such as Carol Kirkwood and Tomasz Schafernaker. But as the climate crisis gains new urgency, our understanding of weather systems and patterns is more important than ever – and the weathermen working here are key to that. Among the last in the world to use such analogue methods as weather balloons, they are guardians of a dying art.

Facebook Twitter Pinterest From left: Met Office weathermen Murray Henry, Marcos Henry and Lori Bennett. Photograph: Robert Ormerod/The Guardian

The Met Office has five other operational locations outside the UK (Antarctica, from October to April; Ascension Island and the Falkland Islands in the south Atlantic; Gibraltar and Cyprus), but none as unreachable as this tiny British overseas territory. The far-flung volcanic outpost doesn’t just filter data into global forecasts to help predict whether your summer bank holiday will be a washout; it plays a vital role in tracking how our climate is changing over time. Added to that, the south Atlantic is a hotbed of geomagnetic activity – something many experts believe is a factor driving the climate emergency. Crammed into Bottom Woods station, little more than a humble portable at the end of the Earth, are complex instruments sounding a warning to anyone who will listen.

Facebook Twitter Pinterest Launching the balloon at 11.15am. Photograph: Robert Ormerod/The Guardian

After precisely 90 minutes, Bennett’s balloon reaches a height of 100,000ft (30,480m), where the air temperature hovers around -80C; the giant latex ball has stretched to the size of a two-storey house. It is used only once and will eventually burst somewhere on the edge of the stratosphere, but not before a mini weather station, known as a radiosonde and attached to the neck of the balloon, can relay back data on temperature, moisture, pressure, visibility and radiation. With Whitney Houston’s One Moment In Time drifting out of the weather station’s FM radio, it is the oddest science lesson you could imagine. Bennett sometimes imagines himself flying away with the blimp, he says, like the balloon salesman Carl Fredricksen and his cartoon house in Disney’s Up: “Just working in this quiet place gives me the freedom to dream.”

As the wind continues to whirl across the balloon launch site, the station manager introduces me to the rest of the team. St Helena’s weather station has been operational since September 1976.

Satellites only do so much. Honestly, there’s still nothing as reliable as a land-based station

Technical manager and islander Marcos Henry, 58, has been working at the station since leaving school at 16. He says the balloon procedure – one daily launch, always at 11.15am – is effectively the same as it was 43 years ago. The weather never stops, he says, although he notes that they used to launch two balloons a day, before cost-cutting measures started to bite. Sunday is now launch-free – and sometimes the four-man team are stretched.

Facebook Twitter Pinterest Hydrogen fills the balloon. Photograph: Robert Ormerod/The Guardian

Today, Marcos is joined by 28-year-old Murray Henry, his island-born cousin, but not Garry Mercury, another (appropriately named) scientific observer; he is at the dentist with toothache. If there are any further staffing issues, one of the local binmen has been trained to act as a substitute. “You can’t really put a value on what we do here,” says Marcos, as a gritty light begins to spill through the clouds. “We have a collective responsibility to gather information, because it affects people’s lives every day – we’re the frontline in Atlantic forecasting.”

I follow the three men into the office, which is topped with VHF antennae and fortified with a clunky array of instruments, including a broken anemometer that once measured wind speed, an obsolete sunshine recorder and a bank of computers that transmit data back to Met Office HQ in Exeter. It feels like a place that exists in a different era. “Satellites only do so much,” says Marcos, with one eye on the readings coming in from the balloon. “Honestly, there’s still nothing as reliable as a land-based station.”

The St Helena unit is just one of 190 stations that make up the Global Climate Observing System (GCOS), which is co-run by the UN, Unesco, the International Science Council and the World Meteorological Organisation to monitor activity in the Earth’s upper atmosphere. As a key station in the south Atlantic, its data is vital for climatological studies, and its old-school methods have made the men unlikely rock stars on the island. “Everyone wants to see the big balloon,” says Bennett.

Facebook Twitter Pinterest Marcos Henry, adjusting a cable in the meteorological station’s ‘weather garden’. Photograph: Robert Ormerod/The Guardian

St Helena is 5,000 miles from the problems of Brexit Britain, boasts black-sand beaches, Galapagos-like giant tortoises and all manner of indigenous birds. Yet that is mixed with reassuringly familiar snapshots of the UK: homes in the British overseas territory are decorated with pictures of the Queen, shops stocked with bottles of HP Sauce and cans of Irn-Bru.

What also characterises the island is its topographical weirdness. With its odd mesh of rainforests and moon-like tablelands, the landscape changes abruptly from Yorkshire Dale to Jurassic Park, while the night skies are a blowout of frighteningly bright nebula. Small wonder Bennett – as well as Charles Darwin and Edmond Halley – fell for the place. As in the UK, there is plenty of talk about the weather, too.

Have its forecasters noticed signs of the climate crisis? Bennett says he has little doubt. The wettest day since the weather station opened came last February, with 49mm of rain in just 24 hours. Marcos remembers a time growing up on the island when streams flowed freely; recently, they have dried and turned to dust. “There have been landslides and rock falls, too,” he says. In the 90s, the island recorded 4,543mm of rain, a figure that soared to 5,148mm over the following decade. So far, from 2010 to this March, the weathermen have seen levels rocket beyond anything on record.

One complex meteorological instrument under the team’s watch is the Marvelesque Sun Sky Lunar Multispectral Photometer, which feeds into a global network to monitor pollutants in the atmosphere; growing levels are a clear indicator of how we need to change our habits. There is also an automated radionuclide station, which recently picked up nuclear particles from the Fukushima Daiichi disaster in 2011, and continues to search for evidence of nuclear tests.

Facebook Twitter Pinterest An anemometer, which measures wind speed. Photograph: Robert Ormerod/The Guardian

Across the island, in the air traffic control tower overlooking St Helena’s airport, another Met Office scientist, Timothy Baker, is contemplating the same clouds. The meteorologist has been at his desk since 4am creating a forecast to ensure the safe arrival of the biweekly aircraft from Johannesburg, the island’s principal connection with the outside world. (The airport opened for commercial flights in 2017.) His hope is that the bank of low stratus to the south will relent in time, otherwise the plane will have to turn around, 1,100 miles into its journey.

“It’s a complex place because of how quickly the weather can change,” he says, as radio static from a console begins to cut through his words. “Four seasons in one day? It’s more like 12. It can flip from sunshine to thick fog within minutes. Sometimes, they can’t see the fuel barrels on the apron [where planes are parked] from five metres.”

As I come to realise, the usual norms rarely apply here. Along with a colleague at Heathrow and a handful scattered around RAF bases, Baker is in the unusual position of being a weatherman embedded at an airport, working in tandem with the Bottom Woods team. Other airports rely solely on remote forecasts.

On the day I leave, clouds are billowing over Diana’s Peak, the mountain that looms to the west of the airport. The plane accelerates and all I can think of is the ends-of-the-Earth weathermen, enveloped in cloud, predicting sun patterns, rain showers and crosswinds. We have become so used to weather updates on TV, radio and phones that we have stopped seeing the act’s grandeur. To visit St Helena – to see Bennett, Marcos and Murray launch their balloons into space – is a chance to glimpse that absorbing strangeness once again.

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