Standing under a tree can be cooler by as much as 18 degrees Celsius, by one estimate
Shade blocks light, and evaporation from leaves adds to the chill.
The joe gardener Show - Organic Gardening - Vegetable Gardening - Expert Garden Advice From Joe Lamp'l · 490-How Leaves Conjure Up Our WorldStep under a tree on a hot day and the temperature can be 12 to 18 degrees Celsius lower than in the sun, according to figures evolutionary biologist Jonathan Silvertown said he has seen reported.
Shade blocks sunlight, and evaporation adds another cooling effect, he says. Trees move large amounts of water up through the canopy, and as that water evaporates from leaves it draws heat from the surrounding air.
He likens the effect to "wearing a wet T-shirt" "but without getting wet." You get the cooling without the wet.
Most people have felt this on a hot day. It works like cooling without a machine, powered only by sunlight and water.
Questions people ask
How much is 12 to 18 degrees Celsius in Fahrenheit?
A difference of 12 to 18 degrees Celsius equals about 22 to 32 degrees Fahrenheit. That is the size of the drop, not the final temperature. On a 95-degree day, that would feel like stepping into the 60s or 70s.
Does the cooling still work when the air is already humid?
Less well. Evaporation slows when the air is already full of moisture, so the cooling effect is strongest in hot, dry conditions. In humid places, shade still helps, but the evaporative chill is smaller.
Do all trees cool the air the same amount?
No. Larger, leafier trees with plenty of water move more vapor and cool more than small or drought-stressed trees. Species, canopy density, soil moisture, and wind all change the result.