The pollen from trees and grasses that produces allergic reactions in millions of people is steadily increasing with rising temperatures, according to the UK's leading pollen specialist.
Pollen seasons are lengthening, and the pollen itself is provoking a more powerful reaction - a situation already being reflected in rising GP consultation rates for hay fever, according to Professor Jean Emberlin, director of the National Pollen and Aerobiology Research Unit.
Hitherto, the direct effects of climate change on everyday life have seemed a long way off. But for the estimated 13 million Britons who annually suffer the misery of runny noses and watering eyes, they have already arrived, as pollen counts head steadily upwards - and more and more people are being affected.
"We are seriously concerned that rising pollen loads are starting to affect a substantial number of people who have never had hay fever before," said Muriel Simmonds, chief executive of Allergy UK (formerly the British Allergy Foundation). "That is coming over loud and clear."
The worsening situation has been dramatically illustrated this week by a giant pollen cloud, mainly from birch and pine trees, that has drifted to England across the North Sea from Denmark and Scandinavia, scattering its fine grains across the land.
Although some pollen is blown here from other countries every year, most goes unnoticed - but Professor Emberlin said this week's cloud, clearly visible on satellite photographs, was the worst in her experience. "It is unusual in its severity this year," she said. Asked it if was the shape of things to come, she said: "It may be."
It follows record pollen counts in parts of Europe this spring. Last Sunday, Denmark had its record count of 4,381 grains per cubic metre of air (pcm), while Vienna has experienced a record of 2,500pcm. At the University of Worcester, where Professor Emberlin's unit is located, a record count of more than 1,000pcm was noted three weeks ago. "Bear in mind that over 80 is considered high," she said.
The likelihood of pollen counts rising because of global warming was pointed out in the last report of the UN's Intergovernmental Panel on Climate Change (IPCC) in 2001. It is not only rising temperatures but also the increase in atmospheric carbon dioxide that is bringing them about that could increase pollen production, the report said.
"There are several aspects to the problem," Professor Emberlin said. "Firstly, the pollen season for trees is coming earlier with climate change. In the UK, over the past 30 years the tree pollen season has got earlier by five days per decade.
"Second, the grass pollen season is tending to go on longer in the summer. Twenty years ago it was probably finished by the end of July. Increasingly, it goes on until the first or second week of August, and this is reflected in GP consultation rates for hay fever.
"Third, there has been a trend in the past 10 years for the effects of grass pollen to become more severe. If plants are stressed by high temperature and/or pollution, they tend to produce more protein on the pollen grain, to maximise their chances of reproduction. It is the protein content which is the allergen, which causes the reaction, so the same amount of pollen grain has a more pronounced effect.
"All of this is caused by changing weather patterns which are consistent with predictions of climate change."
Asked if it meant that the situation for hay fever sufferers was going to get worse, she said: "I don't want to be scaremongering, but, yes - if present trends continue, with earlier start dates for tree pollen and a more severe grass pollen problem.
"There is no doubt that this is happening over large areas of northern Europe. Quite a lot of factors are all pressing towards a scenario where we have an increasing allergenetic load."
Muriel Simmons, the head of Allergy UK, said the rise in people newly experiencing hay fever was marked. She said: "What we're seeing, through our helpline and e-mails, is a steady increase over the last two or three years, and particularly over this last year, in people contacting us who have never had hay fever before. They're in their thirties, forties and fifties, whereas we used to think that in the UK it was young people who got it. They are totally stunned."
There may be additional causes for rising allergy levels, including the so-called "hygiene hypothesis", which suggests that nowadays we live in a cleaner world, and are not so exposed to bacteria when young - so our immune systems are not as robust.
Ms Simmons said it was important for new sufferers to take the precautions that long-term hay fever victims make a part of their lives, as it could go on to produce asthma.
Dani Rutherford, 28, press officer: 'I could feel my nose swelling up'
"I've started suffering in the last four years," said Dani Rutherford, a press officer from London. The 28-year-old said: "It must be karma or something. I used to laugh at people with hay fever because I thought it was ridiculous to be allergic to pollen. I've always been quite sneezy and I thought it was the cat or something.
"Then one summer I was watching a World Cup football match in the pub and I sneezed through the entire match and missed most of it because I had to keep running to the toilet for tissue."
She said that the start of the summer was the worst for her symptoms.
"The other day I was watching television and I could feel my nose swelling up until I couldn't breathe," she said. "It's difficult when I work at music festivals. Last year at Glastonbury it was really hot on the first day and I was a mess. I had to go and sit in my tent until my sneezing calmed down.
"When I eat apples, I get itchiness at the back of my throat, inner ear and the back of my nose and my lips itch and swell slightly. I looked on the internet and apparently that's connected to hay fever too. I always carry around antihistamines and a pack of tissues but I don't watch the pollen count. I definitely moan about my hay fever but I don't let it affect my work or social life."