The Ultraviolet Index (UVI) is a standard international measure of the strength of sunburn-producing ultraviolet radiation at a specific place and time. This scale is linear and open-ended, where higher numbers indicate a greater risk of skin and eye damage from sun exposure. Index values from 0 to 2 are considered Low risk, 3 to 5 are Moderate, 6 to 7 are High, 8 to 10 are Very High, and any reading of 11 or above is classified as Extreme risk.
Identifying the Location with the Highest Recorded UV Index
The location that holds the world record for the highest measured UV Index is the Altiplano region of the Andes Mountains in South America. On December 29, 2003, a world-record ground-level UV index of 43.3 was detected on the summit of Bolivia’s Licancabur volcano, which stands at an elevation of 5,920 meters (19,423 feet). This measurement is more than three times the level considered “Extreme” on the standard UVI scale.
While this record-shattering reading was an isolated event, the high-altitude areas of the Andes, spanning parts of Bolivia, Chile, Peru, and Argentina, consistently experience some of the planet’s most intense ultraviolet radiation. Daily peak UV readings in this region routinely exceed 20, an extraordinary level. For comparison, many equatorial cities regularly see high UVI values, but they rarely approach the extreme measurements found in these specific high-altitude desert plateaus.
Environmental Factors Causing Extreme UV
The extreme ultraviolet radiation levels observed in the high Andes result from a combination of geographical and atmospheric factors. The region’s high altitude is a primary contributor. For every 1,000 meters (3,280 feet) increase in elevation, UV intensity rises by approximately 10 to 12% because there is less atmosphere above to absorb and scatter the incoming rays.
The latitude of these locations, close to the equator, also plays a large role in the intensity of solar exposure. Near the equator, the sun’s rays strike the Earth at a more direct, overhead angle, meaning they travel through the least amount of atmospheric filtering before reaching the surface. This direct path increases the concentration of radiation hitting the ground, particularly around the midday hours.
A third factor is the condition of the protective ozone layer, which naturally absorbs much of the Sun’s harmful ultraviolet radiation. In the Southern Hemisphere, temporary ozone “mini-holes” and seasonal variations can lead to a localized thinning of the layer. This reduction in ozone protection allows a greater amount of intense UV radiation to reach the mountain peaks and plateaus, exacerbating the already high exposure from altitude and latitude.
Surface reflection further contributes to the total exposure, especially in mountainous environments. Surfaces like snow and ice, which are common on high-altitude peaks, are highly reflective and can bounce up to 90% of the UV radiation back toward an exposed person. Even dry sand can increase exposure by about 20%.
Necessary Protection Against High UV Exposure
Limiting sun exposure between 10 AM and 4 PM is the most effective strategy, as these are the peak hours when UV intensity is greatest. Seeking dense shade during these times is a fundamental action. It is important to remember that UV can still be reflected off surrounding surfaces.
Clothing provides a physical barrier and should be the primary method of protection against extreme UV levels. Tightly woven, full-length fabrics are best, and items with an Ultraviolet Protection Factor (UPF) rating offer a quantifiable measure of defense. A wide-brimmed hat, ideally with a brim of at least three inches, is needed to shield the face, neck, and ears.
Generous and frequent application of sunscreen is essential when outdoors. A broad-spectrum sunscreen with a Sun Protection Factor (SPF) of 30 or higher should be applied at least 15 minutes before going outside. Reapplication is necessary every two hours, or immediately after excessive sweating, swimming, or towel drying, which is particularly important at high altitudes where physical activity is common.
The eyes must be protected from extreme radiation to prevent conditions like cataracts or photokeratitis, often called snow blindness. Wrap-around sunglasses that block 99 to 100% of both UVA and UVB rays are necessary to protect the entire eye area from direct and reflected UV light.