Newly installed artificial turf looks magnificent - like a well maintained lawn. But as is so often the case there's a big difference between form and function. It might look like healthy grass, but it functions more like an asphalt parking lot when it comes to microclimate. Everything on earth emits terrestrial radiation based on its temperature. The hotter an object is, the more energy it emits. A fireplace emits a lot of terrestrial radiation and will warm you on a cool day. In contrast, a cold window will not be emitting nearly as much radiation and standing near it will chill you.
A thermal camera takes pictures of objects' temperatures. In the thermal image below, the truck and the asphalt parking lot are about 46C (pink) while the trees in the background are closer to 25C (yellow and green). A person standing in the parking lot would receive a large amount of terrestrial radiation from the asphalt and truck and would, over time, become overheated. Someone standing on the grass near the trees would be receiving a lot less radiation and would feel much cooler.
Now let's look at a thermal image of an artificial turf playing field taken on the same day at almost exactly the same time. The temperature of the artificial turf is even hotter than the asphalt parking lot. It's almost 48C! That's hot enough to cook an egg. And look at the real grass in the foreground. It's about 25C. A person standing on the playing field would be receiving a lot of terrestrial radiation, while a person standing or sitting on the sidelines would be receiving a lot less.
Think about the implications for people using the field. There are times when the heat from the artificial turf would be welcome - say late in the fall when it's cool or cold outside. But during mid-summer when the air temperature and humidity are high and the sun is shining, the last thing you want is to receive additional heat. You certainly wouldn't choose to play sports on a black asphalt parking lot on a hot summer day.
Spectators standing or sitting on the sidelines on real grass and in the shade of a tree would likely feel quite comfortably cool, even on a hot day. But the athletes playing on the artificial turf would be generating internal energy, and this in addition to the hot, humid, sunny conditions would be enough to make them feel very warm or even hot. The additional heat they receive from the artificial turf could put them over the top.
Many of the components of microclimate are totally invisible to the human eye. We can't see the air temperature, the humidity, or the wind. Fortunately we now have cameras that make the invisible terrestrial radiation visible. Now there's no excuse for designing playing fields that are as hot as asphalt parking lots.