Sitting under a beach umbrella on a hot summer day might feel like a smart way to escape the heat. However, new research shows that parasols barely cool you down at all.
Scientists in Austria used a computer model to study how beach umbrellas affect heat. They found that sitting under a parasol makes a person feel only about 1°C (1.8°F) cooler than standing directly in the sun. When the sun is low in the sky, it can even feel 1°C hotter under the umbrella.
The problem comes from the umbrella's fabric. While the fabric blocks direct sunlight, it absorbs heat and can reach temperatures as high as 70°C (158°F). The hot cloth then sends invisible heat, called longwave infrared radiation, down onto the person sitting underneath it.
Trees are much more effective at cooling than fabric shades because they do not trap heat in the same way. Researchers say parasols could work better if people wet the fabric or if makers use materials that reflect less heat. Umbrella users should also remember that shade only gives partial protection from sunburn, as dust in the air can still bounce UV light under the umbrella.