Whether or not you subscribe to the greenhouse effect theory, the dangers inherent in the sun's ultraviolet rays cannot be disputed.
Across the world, UV radiation is the number one cause of skin cancer, a disease that is responsible for thousands of deaths each year. In fact, over 7,000 cases of skin cancer are reported each year in the UK alone, of which 29 percent prove fatal.
Of course, the general public in the West is well aware of the dangers associated with UV rays, and many use UV-blocking sun lotions. What they don't know is that UV rays can pass through many items of clothing with ease.
Since the general practice for applying sun lotion is to only cover those parts of the body that are directly exposed to the sun, that leaves most of the body exposed to carcinogenic radiation.
Evading the radiation
To counter this, many clothing companies have started to include UV-protective fabrics in their clothing, ensuring that a majority of the radiation is stopped before it can reach and damage the wearer's skin.
Two such companies are Craghoppers and Berghaus. Craghoppers is a 41-year-old company specialising in outdoor clothing. Based in Manchester, England, its garments are suitable for use in both British weather and more exotic climes, and its fans include continent-hopping TV personality Michael Palin. Its SolarDry clothes are designed to block UV rays.
Berghaus, meanwhile, is recognised across the globe for its quality outdoor equipment and clothing. This latter range includes the Adventure Travel range, which features anti-UV fabrics in some of its garments. It began in the north of England, but has since reached out into Europe and set up a German office.
This is all well and good, but cynics might wonder why they should bother to invest in UV-protective clothing. After all, they may say, any barrier between the skin and the sun should provide some protection, so why not get any old t-shirt?
Robert Bruce, brand manager at Craghoppers, disagrees. "Yes, all clothing gives protection to some degree," he said, "but you can't necessarily tell just by looking how well it will actually work.
"For example, about two years ago I went around Manchester and bought five t-shirts, none of which claimed to block UV rays.
"All were roughly the same weight and colour and seemed identical in appearance, but when we had them tested independently, one of them tested as fully protective and one proved to be useless at blocking UV radiation. The rest were somewhere in between.
"There was no way to tell without having them tested. So you could take a chance and buy any old clothing - you might get lucky - but you are better off buying from a brand that can guarantee it."
The science behind the shirts
So what is it that makes one shirt protect its wearer brilliantly and another prove useless? It turns out that it's down to a trio of factors: colour, yarn composition and the type of weave used in the fabric.
Of these, managing the colour of the clothing might seem the quickest and simplest way to solve the problem, but it's not quite that easy.
Why? Julie Gretton, materials development manager at Berghaus, explained: "Darker colours typically block more UV rays than lighter colours which allow more UV to pass through to the wearers’ skin. However, light colours are popular for summer clothing since they reflect more heat.
"That's why, when we test fabrics for UV protection, we always look at the worst-case scenario and test the lightest shades of the fabric.”
Of course, relying solely on colour to provide protection will severely limit the customer's options - after all, not everyone looks good in dark green. So in order to allow for lighter colours, some of the protective factor has to be made up by the fibres themselves.
Robert from Craghoppers explained: "A lot of it is actually down to the structure of the molecules within the fibres.
"Filament fibres are bright, shiny and glass-like, so light can pass not only through them, but along them as well. They're not really blocking the sun's rays, only reflecting them.
"Comparatively, some of the more natural materials like cotton have a very rough texture and surface and that actually causes them to intercept a lot more of the light.
"Also, we go for spun yarns rather than filament yarns because they are individual bundles of fibres with ragged edges that can intercept and break up UV radiation as it passes through the small holes in the woven material."
As this suggests, the weaving is important, too; the tighter the weave, the smaller the holes in the fabric and the lower the amount of UV radiation that can make it through the material. If the yarn and the weave are just right, the range of available colours increases massively.
UV coatings: a real wash out
There are other tricks that can be used, too, such as textured clothing. David Brook, a textile expert at the University of Leeds, said: "Obviously, ribbed or textured fabric is going to be better because it scatters and disrupts the radiation.
"The actual pattern and direction of the ribbing doesn't matter - radiation moves in every available direction. You could say that radiation has no orientation."
Another method is impregnating the fabrics with anti-UV chemicals. However, both Berghaus and Craghoppers avoid using this technique in their garments.
Robert explained why Craghoppers refuses to use chemicals: "We don't add anything to make the clothing sun protective because they usually wash out after about 20 washes or so.
"We deliberately avoid anything that changes with the time because we want people to depend on our clothes for years after buying them."
However, washing can still reduce the level of protection offered by UV-blocking garments even if they do not contain chemicals. Julie of Berghaus said: "If you imagine the garments when they're being washed, the weave structures can relax a little bit, allowing more light through.
"So if it is washed repeatedly you would expect to see some changes in the clothing's performance. However, the effects are not usually particularly major and we do take this into consideration when developing the clothing."
Solar so good?
All of this is perfectly good in theory, but unless the fabrics used in the clothing actually do their job, the whole thing is academic.
Ultimately, then, tests are required to see how well the clothing will actually live up to its promises. David Brook explained: "The tests are done on a medical physics machine, which was originally designed for hospital use.
"You basically have a UV source inside a big globe, with a window facing it. You cover the window with the fabric and behind it you put a UV radiation detector. The detector can only measure the amount of UV passing through the clothing.
"The globe ensures that the UV is distributed evenly around the room, because if it were concentrated in some areas and not in others, it wouldn't be a scientifically controlled test."
But this test would be useless without some way to categorise and measure the results. Thankfully, there is a carefully constructed measurement and rating system. Julie explained: "In terms of UV ratings, the results are tested to EN 13758 standard, which lays out how much radiation they are allowed to let through.
"The results are then graded using the ultraviolet protection factor (UPF), which goes from 0 to 50+, with the higher rating being safer.
"Typically the UPF will go up to 50+, which offers the highest level of protection. Depending on the fabric and other properties required, our fabrics' UPF ratings range from 20-50+. One of the industry standards is that you could not claim UV protective properties with a UPF of less than 15."
The system is fairly simple: the lower the amount of radiation passing through the fabric, the higher its rating. If the fabric lets through more than ten percent of UV rays, it will get a UPF rating of less than ten.
If it lets through 3.4 to 5 percent, it will get a rating of 20. This continues to increase until there are virtually no rays passing through the fabric. The system is analogous with the sun protection factor (SPF) used in sun lotions.
However, there is a further complication that the consumer should be aware of when buying UV protective clothing. Robert said: "The UPF is only used when you're measuring the protective qualities of the material.
"If you're measuring the finished clothing, it is known as the clothing protection factor (CPF), and is measured to the same scale.
"You have to be careful, because if the clothing does not cover most of the body it cannot be described as 'sun protective'. Even if I had a fabric that had a rating of 40+ - that's very high protection - I couldn't say that a vest made out of it was sun protective clothing because it leaves too much of the body exposed."
A growing market
It should be obvious by now that both Craghoppers and Berghaus put a great deal of care and attention into creating their UV clothes. But how serious is the demand for such clothing?
Julie believes that public interest is growing. She said: "I think there's an increasing awareness of the need to have protection from the sun, particularly when people are going abroad and know they will be spending time outdoors.
"Obviously, Berghaus equipment is designed for all-year-round use, but we specifically test the UV properties of our Adventure Travel range, because we know that our customers will be wearing that clothing in hot climates."
But Robert believes that people - and the British public in particular - are starting to recognise that UV radiation can be just as deadly at home as it is abroad.
He said: "The UV protection thing is becoming more important all the time. The science has been around for some time, but the recent weather has proved to people in Britain that it's not just an issue when you're going on holiday; it's an issue that affects everybody.
"It's also a self-fulfilling prophecy. Companies have started to notice that there is a large market out there for UV protective products - look at the advertising that Boots have started doing for skin care this year, for example.
"The more they advertise to this market, the more other people become aware of the issue and the more interest is generated. There's a huge market in the UV protection industry and it's still growing. We've only just scratched the surface."