Autumn is officially here…so why is it still so hot? Scientists blame the growing Super El Niño for the strangely warm weather - and say it could last for weeks

While today officially marks the first day of autumn in the Northern Hemisphere, it really does not feel like it in the UK.

After a brief spell of dreary weather, temperatures are climbing back to summer highs, with forecasts predicting 26°C (79°F) in London on Friday.

According to meteorologists, a 'ridge' of high air pressure and the growing effects of climate change are driving the UK's unseasonable weather.

What's more, the growing Super El Niño is starting to shape global weather, having smashed temperature records months before its expected peak.

Record sea surface temperatures brought by the natural climate cycle paired with a background of global warming mean that the UK may experience warmer–than–normal weather in the coming months. 

Dr Lucy Clarke, of Nottingham Trent University, told the Daily Mail: 'It [El Niño] may increase the chances of milder, wetter and stormier weather, especially later in autumn and into early winter. 

'So it could lead to more unsettled weather during the coming months and may bring increased cold spells later in winter.'

Professor Nigel Arnell, a climate scientist from the University of Reading, told the Daily Mail: 'Temperatures are not necessarily record–breaking so far this autumn, but the higher than average temperatures do follow a very warm late winter, spring and summer.'

Professor Arnell says this is due to three factors. 

'One is the general long–term trend of increasing temperatures due to global warming,' he explained.

'The second is the higher sea surface temperatures than normal in the Atlantic – again due to global warming. 

'The third is the persistent position of the Jet Stream, allowing hot air from the south to extend into the UK.'

While the first two factors are gradual trends, the position of the Jet Stream shifts from year to year, creating a natural variability that is superimposed onto a warming background.

According to the Met Office, the UK's unseasonably warm weather began over the Atlantic, where a deep area of low pressure has formed to the west of the UK.

As the week goes on, this will continue to drag warm air up from Europe and subtropical Africa.

At the same time, a ridge of high pressure has built over the UK, setting the stage for settled conditions and bright sunny spells.

As the sun breaks through the cloud cover, temperatures will gradually climb throughout the week.

By Friday, London and the South of England are expected to see temperatures ranging from 20°C (68°F) to 26°C (79°F), while Scotland and the North of England see highs of 16°C (61°F).

Experts say that these weather conditions have lined up the UK for a spell of warm weather even as autumn sets in.

However, the unusually hot weather for this time of year is only possible due to an exceptionally warm background.

Professor Hannah Cloke, a leading meteorologist from the University of Reading, told the Daily Mail: 'Right now there is high pressure sitting over us and drawing in warm air from the south.

'That gives sunny days in the mid–20s even this late in September.'

However, Professor Cloke warns that this 'sits on top of a much bigger picture' of human–caused climate change, which has shifted background temperatures.

'So when the weather pattern lines up for warmth, it gets warmer than it used to,' says Professor Cloke.

A recent rapid attribution study conducted by the Met Office found that this year's record–breaking summer was made 130 times more likely by climate change caused by burning fossil fuels.

Professor Friederike Otto, a climate scientist from Imperial College London, told the Daily Mail: 'Following a record–breaking hot summer, we’re now into an unseasonably warm start to autumn.

'We know that every heatwave is made hotter and more likely by the emissions we’ve put into the atmosphere, primarily from the burning of fossil fuels.'

This unusual heat also comes against the background of a growing Super El Niño.

El Niño is part of a naturally occurring climate cycle called the El Niño Southern Oscillation.

This cycle alternates between a hot phase – El Niño – and a cool phase – La Niña – every two to seven years, with massive consequences for global weather.

During the El Niño phase, warm water builds up near the surface in the equatorial Pacific, driving up global temperatures.

The latest data shows the sea surface temperatures in this critical region are now 3.05°C above the average for 1991–2020 – this has already overtaken the 3.02°C record set in November 2015.

Scientists say it's now looking on track to be the largest in at least 1,000 years – with a possible peak of 4.1°C in November and December.

Professor Cloke says: 'El Niño is now very strong and still growing. It is already shaping weather across the tropics: floods and drought in Central America, wildfire smoke across Southeast Asia, and a very quiet Atlantic hurricane season.

'But El Niño's biggest push on global temperature usually comes a few months after it peaks. So the real global heat boost is still ahead of us, into 2027.'

Experts anticipate that this will push up the average global temperature in the coming months and into next year, leading to above–average temperatures across all land areas this autumn.

According to scientists, this could lead to knock–on effects that may shape British weather throughout the autumn and into winter.

However, scientists insist that El Niño's direct impact on the UK's weather systems will be limited.

'El Niño has a strong grip on the Pacific and the tropics, but a weak and noisy one on our weather. Our autumn will still be driven mainly by the Atlantic and the Jet Stream,' says Professor Cloke.

'Most of the warmth we see now comes from long–term climate change. El Niño adds to it.'