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The UK is currently experiencing its longest heatwave in 12 years and there is no sign of it slowing down.

The Met Office has issued an amber heatwave alert for large parts of England, urging people to “stay out of the sun” between now and Friday.

Monday was the hottest day of the year so far, coming three weeks or so after the hottest temperature of the year was recorded in Wales.

Temperatures are set to rise to 35°C in parts of the UK by Thursday this week, which could be the highest for three years. Temperatures will be slightly lower in Wales , though still pushing 29°C.

The rising temperatures are having an effect on farmers and their livelihoods , as well as several other businesses, and the levels of the UK's reservoirs, lakes and rivers . It is even affecting the water of Cardiff Bay .

Professor Len Shaffrey, Professor of Climate Science at the University of Reading, said: “The UK and Ireland have been experiencing a prolonged hot and dry spell since June, with the first half of summer (June 1 to July 16) being the driest in the UK on record.

“The lack of rainfall has started to impact on water usage, and hosepipe bans have started to come into force in Northern Ireland and the North West of England. The hot and dry spell is also playing havoc with farming. A shortage of lettuce and broccoli is expected in the next few months, whilst the dry weather has pushed up the cost of cattle feed in Ireland by 50%.”

This isn't the first time the UK has experienced a long dry spell or heatwave, of course, with the one in 1976 the one that's most often referred to . But as far back as 1898 newspapers were excitedly reporting them .

However, in contrast to the heatwave of 1976, when the UK was one of the hottest places on Earth (relative to normal), in 2018 countries across the globe are currently experiencing extremely high temperatures.

What is causing the heatwave?

The jet stream

One of the (major) factors in the 2018 heatwave is the jet stream, the core of strong winds some five to seven miles above the Earth’s surface that blow west to east and move weather around the globe. Wind speeds can exceed 200mph but this isn’t felt at ground level.

It is currently looping to the north of the UK, but very weak, meaning the weather is staying in place.

Dr Marie Ekström, research fellow in climate change impacts at Cardiff University, said: “The weather that we are experiencing now is due to a very weak jet stream.

“Its strength and position has great influence on the weather we experience at the surface. What we are experiencing now is a very weak flow in combination with a high pressure system over central Europe. The high pressure system is blocking weather systems from the Atlantic, pushing them northward rather than allowing them to move eastwards towards Europe.”

Sea temperatures

There have been substantial changes to sea surface temperatures in the North Atlantic.

“These are part of a phenomenon known as the Atlantic multidecadal oscillation,” Professor Adam Scaife, of the Met Office, told The Guardian.

“In fact, the situation is very like the one we had in 1976, when we had similar ocean temperatures in the Atlantic and an unchanging jet stream that left great areas of high pressure over many areas for long periods.”

Climate change

So heatwaves are nothing new. But what has changed since 1976 is that the Earth's average temperature has risen.

Professor Shaffrey says: "Global temperatures are increasing due to climate change. The global rise in temperatures means the probability that an extreme heatwave will occur is also increasing. Recent studies have assessed that climate change has increased the probability.

““The current hot and dry spell in the UK is partly due a combination of North Atlantic Ocean temperatures, climate change and the weather. Should weather patterns continue as they are then we might expect this summer will turn out to be as hot and dry as the extreme summer of 1976."

Dr Ekström added: “It is difficult at this point in time to determine to what extent global warming plays a role in this event. Certainly, blocking events and weak jet streams are part of natural variability in the climate system as evidenced by a similar type of event in 1976.

“Global warming acts to enhance the warming as any natural variability is in addition to an ongoing trend of warming. We also know that the land surface is changing with global warming.

"These fundamental changes to the Earth’s surface are likely to have an impact on the atmospheric circulation system and hence the weather we experience on a local level."

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Meteorologist Simon Lee said: "The heatwave is being caused by a persistent area of high pressure over Europe and Scandinavia, which has deflected active weather systems northward, thus giving us dry and warm weather. It’s possible that this is being driven by a region of record-cold sea surface temperatures in the northwest Atlantic which has changed the path of the jet stream. This pattern has become 'locked' and amplified over time, thus giving our record-setting conditions.



"It is impossible to say during an event whether it was caused by climate change - we’ve seen heatwaves before and we will see them again. However, as my tweet showed, temperatures across the globe are currently at near record levels, which vastly increases the likelihood of a heatwave - even if the weather pattern is not so unusual.

"Summer temperatures in the UK have been warming over the last century, and in recent years we’ve seen both record hot summers (2003 and 2006 in particular) and record wet summers (2007 and 2012 in particular). This pattern of varying extremes is expected due to climate change - we shouldn’t expect a dry heatwave summer every year."

Are other countries also suffering from the heatwave?

Japan’s weather agency has declared their extreme heatwave as a “natural disaster”. More than 65 people have died and 22,000 have been treated in hospital. The city of Kumagaya recorded a temperature of 41.1C, the highest ever recorded in Japan.

Almost 50 people have died in wildfires in Greece as temperatures continue to soar.

Sweden is experiencing its strongest heatwave in almost 260 years. The continued dry weather is affecting efforts to put out a number of wildfires in which at least one person has been killed and dozens injured.

(Image: Mats Andersson/TT News Agency via AP)

Africa is also suffering as reports from Algeria claim Africa’s hottest ever recorded temperature was registered in the city of Ouargla, with temperatures hitting an astonishing 51.3C.

A heatwave in Southern California also saw record-breaking temperatures, with certain areas hitting 48.9C.