UK summer: What's happened to the hot weather?
It's fair to say that after the warmest June on record, July has put a bit of a dampener on the British summer. Temperatures have plummeted from the heady days of 30C-plus, while rain and cloud cover have made it feel more like autumn than peak holiday season. So just where has the sunshine gone? It has only been a few weeks since Britain was basking in a heatwave, but the beginning of July signalled a big change. What is known as a 'blocked weather pattern' is to blame, scientists have told MailOnline, and may have helped drive it. Essentially, low pressure arrived at the start of this month - bringing with it cooler temperatures and wetter days - and hasn't shown any sign of shifting. In fact, forecasters don't anticipate the hot weather returning to the UK until mid-August at the earliest, despite Europe entering what is . However, this contrasting weather is no coincidence, according to scientists. Professor Richard Allan, an expert in climate science 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 in the atmosphere become blocked they can cause relentless heat to build in some regions, like we're seeing in parts of north America, southern Europe and areas of Asia,' he said. 'But also intense rainfall and flooding in others, or just persistent cool and showery conditions like the UK is currently experiencing.' Professor Nigel Arnell, of the University of Reading's Meteorology Department, agreed. 'It's the blocking which is making the European heatwave so extreme, so there is a connection 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 strip of air high up in the atmosphere that's responsible for steering weather systems towards the UK from the Atlantic - can also stall weather patterns. If this flow of winds is rushing quickly in a straight line from west to east then the weather often changes day to day. When it weakens and becomes bendy or wavy, however, that's when we get stuck with certain conditions for longer. At the moment that's cooler and wetter weather, but in June it was hot. In fact, most of this year has seen conditions persist for many weeks. For instance, January began unsettled but February was the driest in the UK since 1993, before March was Britain's wettest March on record. April and May were largely cooler than normal before the heat stepped up a notch in June. Why are weather patterns persisting for longer then? Climate change is a distinct possibility, according to some experts. There are studies which suggest that global warming might be making blocked weathers patterns more common. The problem in relation to the jet stream however is that it naturally has waves, so just how much impact, if any, climate change is having is unclear. But Professor Allan added that 'it would be surprising if the unprecedented ocean warming patterns due to human-caused climate change were not disrupting the planetary waves and jet streams of air many kilometres above our head that affect our weather patterns'. With the Arctic region warming more quickly than areas further south there is certainly an argument to be made that climate change is interfering with the jet stream. That is because the flow of atmospheric winds is driven by the contrast in temperatures north-to-south, meaning that if this lessens the jet stream could weaken longer term and become wavy more frequently, sparking a prolonged type of weather. What is more certain, Professor Allan said, is that global warming is 'intensifying the heatwaves, droughts and deluges where and when they occur'. 'Without rapid cuts in the climate warming greenhouse gases we're emitting, these extremes of weather across the world will continue to worsen,' he added. Professor Arnell said climate change 'has two big effects'. 'The first is to raise temperatures in general, so when blocking conditions arise then the resulting heatwave is more intense. 'The second effect is on what we call the dynamics of weather the features such as cyclones, anticyclones, jet streams and blocking patterns. 'This is effect is much more complicated to unravel, but it's fair to say that climate change has disrupted these dynamic systems because it alters the temperature gradients between equator and pole and it has led to warmer sea surface temperatures. 'So whilst we can't say yet that what is happening now is totally due to climate change, we can say that it is consistent with what we expect the effects of climate change to be.' He added: 'We're poking the climate system by adding greenhouse gases, and we therefore can no longer expect to get "normal" weather.' Whether climate change is making blocked weather patterns more likely or not, it is certainly intensifying the extremes when they do get locked in for longer in a certain region. At the moment that's a cold spell for the UK. Last month it was a heatwave. The question is what will follow next month and beyond.