The rain that has drenched parts of the UK and the heat wave that has baked the US can be blamed on carbon emissions that are causing global warming and disrupting the climate.
New evidence suggests one reason why the jet stream responsible for the bad weather may be stuck to the south of the UK is melting Arctic ice, triggered by higher global temperatures.
"There is now no such thing as 'natural' weather," says Peter Singleton, the environmental futures manager at the Scottish Environment Protection Agency (Sepa). "The growing impact of mankind and its resulting pollution has changed both the weather and climate of the planet...starting with deforestation and followed by excessive use of fossil fuels and pollution."
The world is now reaching a "crunch point" at which pollution could cause natural systems to break down and trigger greater change, Singleton argues. This makes unusual or extreme weather events more likely.
"The present unusual weather is entirely consistent with our understanding of how the climate has changed and will change as a result of mankind's impacts," he says.
According to the Met Office, research suggests reducing amounts of Arctic sea ice could be affecting weather patterns. The current levels of ice are at a record low for this time of year.
Warmer air from the Arctic lessens the temperature difference with air from the tropics and slows down the jet stream. That means it is more likely to meander south in the summer and get stuck, causing prolonged poor weather in northern Europe.
Wary of accusations of exaggeration in the past, the Met Office remains cautious. But, says a spokesman: "We do know that the warmer air is, the more moisture it can hold."
As a result of rising global temperatures, there had been an increase of 4-5% in atmospheric moisture. "This means when we do get unusual weather patterns, it's likely there will be more rainfall," Singleton adds. "It seems when it does rain, it is heavier."
Four of the wettest months since records began in 1910 have occurred in the last four years, including the wettest April and June this year.
"If wet months occurred randomly, we would expect only one record to have been broken since 2006," says the Met Office.
Dr Richard Dixon, the director of WWF Scotland, says: "It seems the shifting jet stream may be the first really major impact of climate change on our local weather patterns.
"We'll still have some great summers and washouts but it may be the average summer will now be dull and wet, even as global temperatures rise."
David Crichton, a leading expert on flooding and climate change, says: "People who don't yet believe the climate is changing may be thinking again, as each month seems to bring record-breaking weather."
HOW IT AFFECTS OUR HEALTH
We all know that if we get caught in the rain, we can get the sniffles. But the effect of prolonged poor weather can be subtler – and more dangerous.
The British Medical Association (BMA) points out that extended cloud cover reduces the amount of vitamin D made when our skin is exposed to sunlight. "Vitamin D is known as the sunshine vitamin," says a BMA spokesperson.
"A lack of it is associated not only with inadequate bone mineralisation, but also some cancers and multiple sclerosis (MS). The north of Scotland has one of the highest incidences of MS in the UK."
HOW IT AFFECTS OUR SHOPS
The impact of poor weather on retailers is "overwhelmingly bad", according to Sarah Cordey from the Scottish Retail Consortium, which represents the industry. "It makes life difficult," she says.
Shops have stocked up with summer items such as garden furniture, shorts, floaty skirts and sandals, but they haven't been able to sell them. "Rain suffocates demand for these things," says Cordey, adding that it also has a "depressing effect" on spending.
Apart from the initial lift provided by the Jubilee, June was a "washout".
Only sales of Wellington boots, waterproofs and umbrellas have boomed.
HOW IT AFFECTS HOLIDAYS
Up to 13 million people will be escaping abroad to avoid Britain's dismal summer, says the Association of British Travel Agents (ABTA).
Travel companies reported a 20% boost in business last month, as holidaymakers scrambled to book their get away.
ABTA's Victoria Bacon points out that the bad weather in Britain has been breaking records.
"It is no surprise millions of us are looking to head off overseas for more reliable weather and high temperatures," she says.
Staff at leading holiday firm, Barrhead Travel, are working extra hours to cope with the demand.
"People are literally walking up to our staff and saying, 'Get me out of here'," says the firm's chairman, Bill Munro.
But tourist agency, VisitScotland, is putting on a brave face. Says chairman Mike Cantley: "Our research shows that people do not necessarily come to Scotland for the weather, but for the fantastic range of things to see and do, which can be enjoyed come rain or shine."
HOW IT AFFECTS FOOD
HOUSEHOLDERS are facing increases in the cost of food as wet weather threatens to trigger crop failures and poor harvests.
There have been more that 20 outbreaks of potato blight in eastern Scotland and the Borders in recent weeks. This is much higher than usual, and is blamed by experts on damp, humid conditions.
Crops of barley and wheat are also reported to be struggling with the poor conditions, which could impact on whisky distilling and cereal production. "Farmers said it has not been as bad as this since the 1980s," says Dr Fiona Burnett from the Scottish Agricultural College.
Fruit and salad growers say they are having to throw away their produce because of reduced demand.
"People have not been wanting to eat salads," says James Hallett, chief executive of the British Growers Association.
At the same time, widespread droughts in the US are also hitting corn crops, causing price rises of up to a third over the last month.
Experts say this will push up the costs of food around the world.
HOW IT AFFECTS EVENTS
The rain has caused the cancellation of scores of outdoor events across the country, including festivals, agricultural shows and sporting events.
The Scottish Game Fair at Scone Palace, in Perthshire, had to be called off at the last minute, while the prestigious Taste of Edinburgh food festival had to be abandoned after its site on The Meadows was flooded.
Other victims of the weather include the Luss and Montrose Highland Games, agricultural shows in Dunblane, Dalrymple, Dalkeith, Haddington and Fettercairn, and the Kittochside Heavy Horse Show in East Kilbride. Cricket matches had to be shifted because of waterlogged grounds in Edinburgh, while horse racing in Perth was cancelled.
Across the rest of the UK, community picnics, charity races, Olympic processions, vehicle rallies and horse shows were all called off.
In London, tens of thousands of spectators were deprived of the chance to see pop singers Kylie Minogue and Jason Donovan reunite for a duet.
The Hit Factory Live concert at which they were due to star was cancelled because Hyde Park had become a "mudbath".
HOW IT AFFECTS TRAVEL
Heavy rain has caused flooding, landslides and severe disruption to travellers and homeowners. Last week, the entrance of the Borders General Hospital was flooded, as well as roads in nearby Melrose and Darnick.
The week before, trains in and out of Glasgow Queen Street and Edinburgh Haymarket were halted or delayed for hours after floods and signal damage. Strathclyde Fire and Rescue Service reported 120 calls from householders and businesses worried about flooding.
At the end of June, downpours triggered landslides that blocked both the west and east coast train lines in northern England. Hundreds of people were trapped on a train from London to Glasgow for 15 hours.
The West Highland line between Crianlarich and Fort William was closed for two weeks because a train hit a boulder, loosened by rain, and ploughed down a slope.
Homes and streets in Stockbridge, Edinburgh were flooded after the Water of Leith burst its banks. In Yorkshire, the town of Hebden Bridge suffered three floods in as many weeks, while in Tyneside, more than 20 families are still waiting to return to their homes two weeks after they were flooded.
The floods look set to increase insurance premiums, too. UK Environment Minister Caroline Spelman is talking to the insurance industry about raising money to pay for flood damage, potentially adding 10% to the average family's bill.
HOW IT AFFECTS BEACHES
Two of Scotland's most popular beaches have been polluted in breach of basic safety limits because of heavy rain, according to the Scottish Environment Protection Agency (Sepa). Prestwick, in South Ayrshire, and Stonehaven, in Aberdeenshire, have become the first bathing waters in Scotland this summer to fail sewage contamination limits. They have both recorded two or more water samples with excessive faecal contamination since testing began in May. According to Sepa, the most likely cause of the pollution is the recent downpours, as rain can cause sewers to overflow.
The failure at Prestwick "was likely caused by recent rainfall", says Sepa. At Stonehaven, problems occurred because "a period of persistent and intermittently heavy rainfall coincided with a pollution incident on the Maxie Burn".
A further six beaches have recorded a single sample failure, and just need a second to fail for the season. They are Heads of Ayr and Millport Bay in Ayrshire, Brighouse Bay in Dumfries and Galloway, and St Andrews East and Elie, Fife.
Calum Duncan from the Marine Conservation Society in Scotland says: "With the climate likely to get more unpredictable, and bathing water standards set to get more stringent in 2015, it is imperative that investment continues."
The rain is being blamed for other environmental problems. Gardeners are being besieged by slugs and snails, while the BBC naturalist, David Attenborough, has warned butterfly populations could crash.
Experts are reporting an increase in the number of midges, with one site trapping more than 4.5 million since May 10.
WILL IT EVER STOP?
There is not much prospect of a dramatic improvement in the weather. According to the Met Office's latest 30-day forecast, "the recent changeable weather looks like the most likely scenario as we head through the rest of July and into August".
There is a chance of showers today, and it is likely to be cloudy early this week, with further rain expected from mid-week.
"It then currently looks as though the weather will consist of typical British summer weather, with some further spells of rain but also a few more fine days," says the Met Office.
"What we're not expecting is rainfall of the intensity that we've seen over the last few weeks. Similarly, a spell of prolonged, dry and sunny weather also looks unlikely."
CAN WE STOP THE RAIN
Scientists around the world have used a technique known as "cloud seeding" to try to control when it rains.
But because weather systems are so complex, it is unpredictable, and its effectiveness has been disputed.
Silver iodide, or dry ice, is dispersed into clouds via planes, rockets or ground generators.
The aim is to accelerate the natural process of precipitation.
It was famously used by China to prevent rain during the opening and closing ceremonies of the 2008 Olympics in Beijing.
The problem is predicting exactly when and where the rain will fall.
Jim Dale, from British Weather Services, pointed out that if cloud seeding were used to try to protect the London Olympics from rain when the Games get under way, it could just end up falling on Reading or Slough instead.
A TALE OF TWO SUMMERS
Scotland has had two summers. There's been the long, depressingly dark and damp one endured by millions in the south and east, and the cheerfully sunny and dry one enjoyed by thousands in the northwest highlands and the Western Isles. So while there have been floods in Lothian and the Borders, there have been droughts in Stornoway and Skye and Lochalsh. While city-dwellers have piled up the sandbags, islanders have splashed on the sun cream – and been urged to use less water flushing their toilets.
Figures released by the Met Office make the point in dramatic fashion. Across the UK, June was the wettest it's been since records began in 1910 with 145.3mm rain, as was April with 126.5mm.
The south of Scotland was well and truly drenched in June, with Dumfriesshire receiving 221.4mm of rain, 2.67 times the average for the month. But Sutherland, and Ross and Cromarty, in the north had only 55.6mm and 56.5mm, just 60% of their monthly averages (see map).
The main reason for the unusual weather patterns is that the jet stream has got stuck to the south of the UK. This is a band of fast-moving winds moving from west to east across the Atlantic high up in the atmosphere.
According to the Met Office, the jet stream guides rain-bearing low-pressure systems that regularly move across the Atlantic. Normally in the summer it would be to the north of the UK, and would drag bad weather away from our shores.
But this year it has remained to the south of the UK, giving us weather systems we are more accustomed to seeing in the winter. "The jet stream, like our weather, is subject to natural variability," says a Met Office spokesman.
"We expect it to move around and it has moved to the south of the UK in summertime many times before in the past. It has, however, been particularly persistent in holding that position this year – hence the prolonged unsettled weather."
But it's not just the UK's weather that's been affected. The track taken by the jet stream has also caused floods near the Black Sea in Russia, and an unprecedented heat wave in large parts of the US.
The US has just experienced the warmest first six months of the year since records started, with blisteringly hot record-breaking temperatures in many places. Last week 1,000 drought-stricken counties across 26 states were officially declared disaster areas.
According to the US authorities, 56% of the country is now experiencing drought conditions. There has also been a rash of fierce wildfires in Utah, Idaho, Colorado, Arizona and New Mexico.
"The recent heat and dryness is catching up with us on a national scale," said Michael Hayes, director of the US national drought-mitigation centre.