Britain’s 2026 drought may signal a climate tipping point

If climate change is altering circulation patterns that determine how and where anticyclones form, the brutal drought and heat that hit southern England in 2026 could become the norm — and leave Britain little time to adapt, warns Tim Palmer.

Some experts say this is merely what long-standing climate predictions expect — “hotter drier summers”. But that familiar prediction does not explain what happened this summer, and understanding why matters urgently if Britain is to be prepared for next summer and those immediately after.

What “hotter drier summers” explains — and what it does not

The phrase “warmer wetter winters, hotter drier summers” describes the thermodynamic aspect of climate change: the generic consequence of warming surface temperatures from greenhouse-gas emissions. A warmer atmosphere necessarily holds more water vapour.

With more humid air, the standard low-pressure systems that bring rain to the British Isles in winter will bring even more rain under climate change. In summer, where those low-pressure systems are suppressed by the reduced equator-to-pole temperature gradient — a consequence of the Sun moving northward — the warmer air will dry the land further, reducing rainfall. The physics behind this thermodynamic signal is simple and well understood.

None of that, however, is directly relevant to the drought of 2026. The proximate cause was a persistent high-pressure system — an anticyclone — sitting over much of western Europe from late spring onwards. It steered rain-bearing weather away from Europe. To understand why it was so dry and hot, we must first understand why that anticyclone was so exceptionally persistent.

A persistent anticyclone over western Europe

From late spring, that blocking anticyclone dominated western Europe. By deflecting the usual Atlantic lows, it shut off rainfall and locked in heat. The question is whether that persistence was bad luck or a sign of a changing climate system.

Two explanations — chance or climate dynamics

Broadly, there are two possibilities.

The first is that the anticyclone was part of the internal chaotic variability of climate, with nothing directly to do with climate change. If so, the likelihood of a similarly persistent anticyclone in 2027 is rather small. More normal circulation patterns would be expected next summer. The thermodynamic imprint would still remain — 2027 would be warmer and drier than 20th-century summers — but not the extreme drought and persistent heat seen this year.

The second, much more disturbing possibility is that the persistent anticyclone has itself been made more likely by climate change. In that case climate change is not only affecting the thermodynamics of the atmosphere but also its dynamics.

That distinction is crucial, Palmer argues. Understanding climate change at the regional level means seeing climate not just as a giant steam engine warming and humidifying as more fossil carbon is added, but as a system of cogs and gears — the atmosphere and oceans — whose forces and movements, including the jet streams that determine how and where anticyclones form, must be tracked and predicted.

Are persistent summer anticyclones becoming more frequent?

There is observational evidence that persistent anticyclones are indeed becoming more frequent in summer and are thus correlated with the rise in global temperatures. Producing model data that support those observations is challenging: unlike the thermodynamic aspect, the dynamics of climate change are exceptionally complex and highly non-linear, and can only be addressed quantitatively using the most advanced climate models.

Taken to the extreme, it is possible that we may shortly pass a kind of tipping point where the dynamical effects have become so strong that persistent anticyclones will become overwhelmingly likely each and every summer. If that is the world we now face, there is no luxury of adapting over the coming decade or two. Adaptation would need to happen immediately.

Why current models struggle to see the risk

Some climate modellers will think that alarmist. The most comprehensive global climate models do not support a prediction where persistent anticyclones become a feature of every summer.

But those same models struggle to simulate the type of persistent anticyclone observed this year, probably because they lack sufficient spatial and temporal resolution to represent the turbulent interactions between different scales in the atmosphere. Those so-called scale interactions are known to be important in maintaining anticyclones over long periods, like the Great Red Spot on Jupiter.

For Palmer, the failure to simulate this potential tipping point in current models is not a reason to be complacent but a reason to urgently improve models.

The El Niño wrinkle for Britain

There is an additional wrinkle: El Niño is on the way. In Britain, Palmer expects this transient warming of the tropical Pacific Ocean to have its biggest effect in winter, with the coming winter wetter than normal at first, but perhaps drier than normal later.

There is much variation in European weather from one El Niño event to another. If this one brings below-average rainfall this winter, reservoirs will not be topped up before next summer, with potentially very serious consequences if another persistent anticyclone follows.

What to do before next summer

Palmer has argued for many years that national climate centres around the world should pool human and computing resources to enable ultra-high-resolution global models to be built. Knowing whether we are passing major climate tipping points is, he writes, one of the most important and urgent scientific questions. If humanity works together, it can be resolved quickly.

On practical policy, he asks what emergency measures Britain could introduce now to mitigate a repeat of 2026 in 2027, especially if the intervening winter is not as wet as needed. Does the country need desalination plants, for example? At the least, government agencies need to think about this, urgently and collectively. There is no time to lose.

Tim Palmer is Royal Society Research Professor Emeritus at the Department of Physics, University of Oxford.

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