Why do we sunburn so easily at high elevations?

Published: Jun. 14, 2016 at 6:23 PM CDT
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Why do sunburns occur so quickly at higher elevations?

Before we get to the full explanation, I want to debunk a popular myth. Many people believe that because we’re at a higher elevation in Wyoming, we’re “closer to the sun” and that causes us to sunburn more easily. If that was the main cause, we would burn the easiest in winter because that is actually when the sun is closest to the earth. The difference between the winter and summer months is simply the angle of the sun. The sun shines directly over the northern hemisphere in June which not only gives us much warmer temperatures, it also intensifies the sun’s rays. A simple comparison is if you shine a flashlight directly on your hand at a far distance, it will still be much brighter than if you moved the flashlight closer but tilted it at an angle. Chances are, you’ll also be able to feel some heat from the flashlight when you shine it directly on your hand and very little, if any heat when you tilt it at an angle. This same effect happens with the sun.

So if the sun greatly intensifies throughout the entire northern hemisphere during the summer months, why do higher elevations feel that effect more than lower elevations at the same latitude? The simple answer is that the sun has less atmosphere to travel through. In a study conducted by Ronald O. Perelman with the Department of Dermatology at the New York University School of Medicine, for every 1,000 feet of elevation you climb, you’ll experience an 8-10 percent increase in ultraviolet intensity. That means that at an elevation of just over 6,000 feet here in Cheyenne, you’re exposed to as much as 60 percent more sun than you would be if you were at the same latitude at sea level.

The intensity of the sun decreases greatly the longer the rays have to travel because the light is scattered, reflected, and absorbed more frequently along its journey. Any particles in the atmosphere such as dust, pollution or moisture will help to scatter light and decrease UV intensity. Also, cloud cover actually reflects a lot of the light directly back into space before it ever reaches the ground. This means that cloudy areas, regardless of elevation, are less susceptible to intense UV radiation.

This doesn’t mean you’re safe from the sun when visiting lower elevations. Although burns happen far more quickly in higher elevations than at lower elevations with the same latitude, keep in mind that latitude does make a huge difference. In fact, you’ll find similar UV levels in Florida compared to some of the highest elevations in the United States simply because the sun is at a higher angle over Florida. To be exact, the sun is directly over latitude of 23.5 degrees north during the summer solstice.

This is important to keep in mind throughout the next few months, especially if you have visitors from out of town who may not know how much of an effect elevation can have on the sun intensity.

Do you have a weather question that you want answered? Email me at crystal.harper@kgwn.tv