UK summer: What’s happened to the hot weather?

It’s fair to say that July, after the warmest June on record, has put a bit of a damper on Britain’s summer.

Temperatures have plummeted since the blustery days of over 30°C, while rain and clouds made it look more like autumn than peak season.

So where did the sun go? It’s only been a few weeks since Britain basked in a heat wave, but the start of July marked a big change.

What’s known as a “blocked weather pattern” is to blame, scientists have told MailOnline, and climate change may have contributed to it.

Essentially, the low pressure came early this month — with cooler temperatures and wetter days — and showed no sign of shifting.

In fact, forecasters don’t expect hot weather to return to the UK until mid-August at the earliest, despite Europe heading into what is expected to be its warmest week on record.

However, this contrasting weather is not a coincidence, according to scientists.

Professor Richard Allan, a climate science expert at the University of Reading, told MailOnline that atmospheric Rossby waves – or planetary waves – created by the Earth’s rotation were partly responsible for the two extremes.

“When giant planetary waves get blocked in the atmosphere, they can cause relentless heat in some regions, as we’re seeing in parts of North America, southern Europe and parts of Asia,” he said.

“But also heavy rainfall and flooding in others, or just persistent cool and showery conditions as the UK is currently experiencing.”

Professor Nigel Arnell, from the Meteorology Department at the University of Reading, agreed.

“It’s the lockdown that makes the European heat wave so extreme, so there is a link between the hot conditions in Europe and the windy/cool conditions in the UK.”

But it’s not just planetary waves that get blocked.

The jet stream – a fast-moving swath of air high in the atmosphere responsible for sending weather systems to the UK from the Atlantic Ocean – can also block weather patterns.

If this wind current rushes quickly in a straight line from west to east, the weather often changes from day to day.

However, when it weakens and becomes pliable or wavy, we are stuck with certain conditions longer.

At the moment that is cooler and wetter weather, but in June it was warm. In fact, conditions have persisted for weeks for most of this year.

For example, January got off to a turbulent start, but February was the driest in the UK since 1993, before March was Britain’s wettest March on record.

April and May were cooler than normal for the most part before the heat kicked up a notch in June.

So why do weather patterns last longer? According to some experts, climate change is a clear possibility.

There are studies suggesting that global warming blocked weather patterns are becoming more common.

The problem with the jet stream, however, is that it naturally has waves, so how much of an impact climate change has is unclear.

But Professor Allan added that ‘it would be surprising if the unprecedented ocean warming patterns due to human-induced climate change did not disrupt the planetary waves and jet streams of air many miles overhead that affect our weather patterns’.

With the Arctic warming faster than areas further south, there is certainly an argument that climate change is disrupting the jet stream.

That’s because the flow of atmospheric winds is driven by the temperature contrast from north to south, meaning that if this decreases, the jet stream could weaken over the long term and become wavy more often, causing a long-term form of weather.

What is more certain, Professor Allan said, is that global warming is “amplifying heat waves, droughts and floods where and when they occur.”

“Without rapid cuts in the climate-warming greenhouse gases we emit, these extreme weather events will continue to worsen around the world,” he added.

Professor Arnell said climate change has ‘two major consequences’.

“The first is to increase the temperature in general, so if blocking conditions develop, the resulting heat wave is more intense.”

“The second effect relates to what we call weather dynamics – features such as cyclones, anticyclones, jet streams and blocking patterns.

‘This effect is much more complex to unravel, but it’s fair to say that climate change has disrupted these dynamic systems because it changes the temperature gradients between the equator and the pole and it has led to warmer sea surface temperatures.

“So while we can’t yet say that what’s happening now is entirely due to climate change, we can say it’s consistent with what we expect from the effects of climate change.”

He added, “We’re poking the climate system by adding greenhouse gases, and so we can no longer expect to get ‘normal’ weather.”

Whether or not climate change makes blocked weather patterns more likely or not, it certainly amplifies the extremes when they’re locked into a particular region for longer.

At the moment that is a cold snap for the UK. Last month it was a heat wave. The question is what will follow next month and beyond.