Thunderstorms and climate change threaten UK air travel disruption

As the country sweltered through one of the many heatwaves of a baking summer in late June, towering thunderclouds were gathering over the south of England and across much of northern Europe. It was a Saturday, and with the holiday season getting under way, thousands of passengers were heading to London's Heathrow and Gatwick airports to catch flights abroad. It was always going to be a very busy day.

What followed, however, was chaos for travellers. As air traffic controllers struggled to route aircraft around the storms, airspace became heavily congested and many planes due to fly were simply forced to wait on the ground. In the end, some 900 flights to and from both airports were delayed, some by up to 11 hours. Dozens more were cancelled. At airports across Europe, passengers expecting to fly into London also faced long waits and uncertainty.

The weather in the UK may now have cooled, and passengers may soon forget their experiences. But some within the industry believe what happened in June should be seen as a warning.

The timing in this case was clearly unlucky. But there are concerns that such incidents are only going to become more common as the effects of climate change mount up around the world and weather systems are likely to become increasingly unstable, making disruption more likely and adding to costs for airlines, airports and travellers.

Tim Atkinson, an airline risk consultant and former pilot, says the very crowded skies over the UK and northern Europe mean the region is particularly exposed.

He thinks there is a real risk, for example, that all of London's airports could be affected by storms at the same time, potentially with major consequences in the air and on the ground.

"What we're seeing now is very rapid climate change," he says.

"We're going from the kind of weather activity which takes out an airport, and which the system kind of copes with… to a situation where, with very little predictability, it would be possible to lose all of the London airports from real-time operation quite swiftly and with little notice".

Such a scenario, he thinks, would make the disruption for passengers caused by the incident in June seem relatively minor – and could even put lives at risk. But how likely is it?

For controllers at National Air Traffic Services's (NATS) main control centre in Swanwick, Hampshire, thunderstorms are a major preoccupation. When I visit, it is a hot and humid day, there are ominous dark clouds in the sky, and heavy, thundery downpours are hitting the surrounding region.

In Terminal Control, the part of the building responsible for flights heading to or from airports in London and southern England, those same storm cells are being monitored continually. Their progress is tracked on large radar screens, while at the same time weather forecasts are carefully scrutinised.

Air traffic tends to come in waves during the day. Right now, at lunchtime, it is relatively quiet and the storms have yet to affect major routes. But with activity expected to intensify in the afternoon, staff are already preparing for what could be a tricky few hours.

Stormy weather can shrink the available airspace, meaning traffic has to be restricted and rerouted. If planes are unable to land at one airport, for example due to high winds, they may need diverting to another. But that can create its own problems; if too many unscheduled aircraft land at an already busy airport, it might not have sufficient infrastructure to accommodate them all.

Planes need fuel and somewhere to park. Passengers need food and facilities. Ultimately, if there isn't space, it can simply refuse to accept all but emergency traffic.

This is where the scenario set out by Atkinson comes in. He warns of a situation where traffic is diverted from Heathrow, Gatwick, Luton and Stansted at the same time, leaving aircraft coming in across the Atlantic and a large number of European flights all looking for somewhere to land at the same time, and some with dwindling fuel reserves.

This would at the very least create serious disruption for passengers, who might end up hundreds of miles from their destinations. But it could also, he thinks, create "a very serious risk event, such as an aircraft running out of fuel in the sky".

Aircraft are legally required to carry enough fuel to take them to an alternative airport if necessary, and to allow them to fly for an extra 30 minutes on top of that.

Not everyone shares Atkinson's concern. Former airline executive Andrew Charlton, who manages the Swiss-based consultancy Aviation Advocacy, thinks the risk is low.

"You've always got to imagine the worst-case scenario", he says. "But I also think we need to keep that worst case in context.

"Yes, it's possible to imagine it. But I'm also fairly comfortable with the ability of this industry to react well and make good decisions… of all the things that wake me up at 3am…this is not the top of that list."

Thunderstorms are caused by what is known as convective activity, where moist air close to the ground warms rapidly and rises quickly. As it rises, it expands and cools, allowing the moisture it carries to condense, forming large clouds. More heat means more convective energy, potentially creating instability. In addition, for every degree the Earth warms, the atmosphere can hold about 7% more moisture, increasing the probability of heavy rainfall.

It is not clear whether this means we will actually get more thunderstorms in the UK and across Europe, as so many variables are involved beyond the simple matter of energy and moisture. Some parts of the world may even get fewer. However, studies have shown that higher latitudes, particularly in the northern hemisphere, will see the biggest increases in favourable conditions for storms to form, and those that do may be more violent. According to the UK's Met Office, "while we may not see more thunderstorms overall, the ones we do experience could be more impactful".

Where possible, pilots will avoid flying through convective weather. Even though aircraft are designed to cope with severe conditions, storms can produce intense turbulence, capable of damaging the structural frame of the plane, as well as throwing people around the cabin if they are not strapped in. Hail can also be a big problem, potentially cracking windscreens or causing engine problems. So, however much inconvenience it may cause passengers, crews will invariably put safety first.

Onboard weather radars can help aircrew to see up to 320 nautical miles ahead. They also have access to live weather forecasting resources online. But thunderstorms can move quickly and, according to Prof Guy Gratton, an expert in aeronautics at Cranfield University, these systems are essentially "tactical rather than strategic". In other words, although they enable pilots to see storm cells on their screens from a relatively short distance away, and request a diversion, they do not allow for detailed long-distance planning.

The result is that unplanned diversions often happen late in flight, which is likely to mean burning more fuel. If storm delays do become more common, says Andrew Charlton, then aircraft will have to load more fuel as a matter of course, in case there is trouble brewing ahead. "Aircraft are going to have to fly further, and they're going to have to factor in the assumption they're going to fly further," he says. For an airline, fuel is one of its major costs – and if the fuel bill goes up, he says, it is inevitable passengers will pay more.

More intense storms would be likely to make air traffic management in busy regions harder and potentially lead to more delays and cancellations. However, it is possible some of this could be mitigated using new technologies.

Both Heathrow and Gatwick, for example, have moved away from mandating minimum distances between incoming aircraft in favour of a system which continually calculates spacing times based on wind speeds and aircraft types. In practice, this is meant to allow controllers to reduce the distance between landing aircraft, particularly in high winds, and get them on the ground more quickly. According to NATS, it has successfully improved landing rates and reduced delays by a significant margin.

However, there could be other effects from more severe storms as well. Heavier rainfall, for instance, increases the likelihood of flooding. In a worst case, this can paralyse airport operations, as happened in April 2024 when torrential downpours hit Dubai International Airport. It briefly had to close its runways, while disruption lasted for two days. More than 1,200 flights were cancelled, affecting tens of thousands of passengers.

The problem of clear-air turbulence is also a real one. It cannot be seen, and is becoming increasingly common as the climate warms.

This is when air moves violently at high altitudes with no clouds or other visual cues to help a pilot avoid it. For passengers, it usually only means a little bit of bumpiness, but occasionally it can be a lot more serious. On 1 March 2023, for example, a Lufthansa flight from Austin, Texas to Frankfurt encountered what the airline described as "brief but severe" turbulence.

Those aboard described how passengers and flight crew were thrown around the cabin as the plane suddenly lost altitude. After it made an emergency landing in Washington DC, seven people were taken to hospital.

While still rare, this kind of turbulence is already much more prevalent than it used to be and is likely to become even more so.

"You know the projections are pretty dire: doubling, trebling or worse in the amount of severe turbulence on many busy flight routes around the world," says Paul Williams, a professor of atmospheric science at the University of Reading. He says incidents over the North Atlantic have increased by 55% since 1979.

Nevertheless, he remains confident solutions can be found, including improvements to forecasting and making use of laser-based technology.