What is the UV Index (and Why Should I Care About It)?

iStock
iStock

We’re so used to running for cover when we hear a rumble of thunder during the summer that it’s easy to forget that we’re just as exposed to the elements under a beautiful, cloud-free sky. Whenever the Sun's out (and even when it isn't), we're at risk for sunburns, which are caused by the Sun's ultraviolet, or UV, radiation. But just how serious is that risk on a given day? That's where the UV Index comes in.

Ultraviolet radiation falls next to visible light on the electromagnetic spectrum. The two wavelengths of UV rays that can cause injury are called UVA and UVB rays. Both types are dangerous over long periods of time, but UVB rays are thought to be the most dangerous. Excessive exposure to UVA and UVB rays can cause cell death, leading to painful sunburn, or, over time, some forms of skin cancer.

Earth’s atmosphere does a pretty good job protecting us from harmful UV rays, but it doesn’t completely block them out. Most ultraviolet radiation is absorbed by the ozone layer. Ozone is gas that’s usually situated more than twice as high above sea level as the cruising altitude of a commercial airliner. In the 1970s and 1980s, there was a concerted effort to eliminate the use of chemicals that deplete the ozone layer as people began to understand what its depletion would mean: overexposure to dangerous UV rays for humans, animals, and plants.

UV Index Forecast
A map of the UV Index on June 9, 2017.
NOAA/NWS/EPA

The UV Index was developed to tell us the level of solar radiation on a particular day, and thus, how susceptible we are to a sunburn. The UV Index is an open-ended scale that starts at 0, indicating the lowest level of danger, with the risk gradually increasing through a UV Index of 10. Any value above 10 indicates an extreme risk for harm from UV rays, with sunburns and eye damage occurring in just minutes.

The index is compiled daily using factors like ozone concentration in the atmosphere, expected cloud cover, and the elevation of a certain point above sea level. Greater ozone concentrations, more clouds, and a lower elevation will help prevent UV rays from reaching the ground. A bright, hot, sunny day can easily cause the UV Index to soar above 10.

Risk from UV rays doesn’t end with sunshine pouring out of the sky. Ultraviolet radiation can also be reflected, meaning that the danger for sunburns and eye damage increases around bright surfaces like a beach or the shimmering waters of a swimming pool. If your eyes have ever hurt after looking at snow on a sunny day, that painful condition is directly caused by UV rays reflecting off of the white surface.

One easy way to protect yourself from harmful UV radiation is to cover up. But clothing and hats don't deflect all UV rays. That's where sunscreen comes in. The best sunscreen to use is one that’s rated for both UVA and UVB protection with an SPF (sun protection factor) of at least 15 or higher, according to the FDA. (The American Academy of Dermatology suggests one with an SPF of 30 or higher.) A sunscreen’s SPF doesn’t relate to the amount of time you can spend in the sun, but rather the amount of protection offered by a particular formula. An SPF of 15 blocks 93 percent of UV rays, while SPF 50 is said to block 98 percent. (Some argue that sunscreens over SPF 30 are no more effective.) Whichever SPF you choose, don't forget the sunglasses—specially rated pairs can protect your eyes from radiation, and also help you channel your inner celebrity. Sounds like a win-win to us.

Wayfair’s Fourth of July Clearance Sale Takes Up to 60 Percent Off Grills and Outdoor Furniture

Wayfair/Weber
Wayfair/Weber

This Fourth of July, Wayfair is making sure you can turn your backyard into an oasis while keeping your bank account intact with a clearance sale that features savings of up to 60 percent on essentials like chairs, hammocks, games, and grills. Take a look at some of the highlights below.

Outdoor Furniture

Brisbane bench from Wayfair
Brisbane/Wayfair

- Jericho 9-Foot Market Umbrella $92 (Save 15 percent)
- Woodstock Patio Chairs (Set of Two) $310 (Save 54 percent)
- Brisbane Wooden Storage Bench $243 (Save 62 percent)
- Kordell Nine-Piece Rattan Sectional Seating Group with Cushions $1800 (Save 27 percent)
- Nelsonville 12-Piece Multiple Chairs Seating Group $1860 (Save 56 percent)
- Collingswood Three-Piece Seating Group with Cushions $410 (Save 33 percent)

Grills and Accessories

Dyna-Glo electric smoker.
Dyna-Glo/Wayfair

- Spirit® II E-310 Gas Grill $479 (Save 17 percent)
- Portable Three-Burner Propane Gas Grill $104 (Save 20 percent)
- Digital Bluetooth Electric Smoker $224 (Save 25 percent)
- Cuisinart Grilling Tool Set $38 (Save 5 percent)

Outdoor games

American flag cornhole game.
GoSports

- American Flag Cornhole Board $57 (Save 19 percent)
- Giant Four in a Row Game $30 (Save 6 percent)
- Giant Jenga Game $119 (Save 30 percent)

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Expeditions Gather Climate Change Clues on Mount Everest in Two New Documentaries

Team members climb up a slope during the expedition to find Sandy Irvine's remains on Mount Everest.
Team members climb up a slope during the expedition to find Sandy Irvine's remains on Mount Everest.
Matt Irving/National Geographic

Two one-hour documentaries premiering tonight reveal what Mount Everest is really like—and what scientists can learn from studying it.

Both docs are produced by and airing on National Geographic. In Lost on Everest, premiering at 9 p.m. EDT, climber Mark Synnott and Nat Geo photographer Renan Ozturk lead a team of seasoned mountaineers on a mission to discover what happened to Andrew “Sandy” Irvine, who vanished with fellow explorer George Mallory during the first Everest climb in June 1924. While Mallory’s body was located by a BBC-sponsored operation in 1999, Irvine’s exact fate has remained a mystery for nearly a century since his disappearance. As Synnott and his companions search for evidence, they encounter their own harrowing set of obstacles, from hurricane-force winds to medical emergencies.

Climbers on Mount Everest
Climbers ascend the Khumbu Icefall, a notoriously dangerous section of the summit route.
Mark Fisher/National Geographic Society

But Mount Everest isn’t only a challenge for adventure-seekers and intrepid investigators—it also holds thousands of years’ worth of information about how climate change has altered the environment, which can help scientists predict its future effects. In Expedition Everest, airing at 10 p.m. EDT, actor Tate Donovan narrates the journey of an international group of scientists and climbers with an ambitious set of data-collecting objectives.

One task is to use drones, laser scanners, and cameras to capture footage of every inch of the ascent, so researchers can create a 360-degree portrait of the mountain and track how glacial melt alters the landscape in the coming years. Since the Himalayas contain the water supply for roughly one-fourth of the world’s population, the increase in glacial melt—which has already doubled since 2000—could threaten the futures of billions of people living in the region.

Scientists drill ice cores on Mount Everest
Mariusz Potocki and members of the National Geographic and Rolex Perpetual Planet Everest Expedition team collect the highest-ever ice core at 8020 meters (26,312 feet) near the South Col of Everest.
Dirk Collins/National Geographic Society

Even more immediate is the risk of flash floods, which are difficult to predict without a constant feed of weather data from high altitudes. Another goal of the expedition is to install weather stations at five locations along the climbing route, which will monitor temperature, humidity, air pressure, wind speed, and other factors that help alert meteorologists to an impending flood.

Some researchers have joined the expedition to drill deep into the ice at an altitude above 8000 meters (26,000 feet)—Mount Everest's "death zone"—and collect ice cores. These long tubes of ice reveal how the atmosphere has changed over thousands of years. Others are collecting similar cores of sediment at the bottom of a lake, as well as examining how plant and animal life has adapted to the warming temperatures and rising water levels.

Overall, Expedition Everest illustrates how the Himalayas function as an early indicator of what climate change will do to other places.

As climate scientist Anton Seimon explains in the documentary, “We’re getting a window into what the rest of the world is starting to experience—and likely to experience in growing proportions.”

You can watch the double feature tonight, June 30, at 9 p.m. EDT on National Geographic.